SECTION 6C2-1 GENERAL INFORMATION - V8

ENGINE

CAUTION

This vehicle will be equipped with a Supplemental Restraint System (SRS). A SRS

will consist of either seat belt pre-ten sioners and a driv er’s side air bag, or seat belt

pre-tensioners and a driver’s and front passenger’s side air bags. Refer to

CAUTIONS, Section 12M, before performing any service operation on or around SRS

components, the steering mechanism or wiring. Failure to follow the CAUTIONS

could result in SRS deployment, resulting in possible personal injury or

unnecessary SRS system repairs.

1. GENERAL DESCRIPTI ON

The engine used in this vehicle uses an Powertrain Control Module (PCM) to control exhaust emissions while

maintaining excellent driveability and fuel economy. The PCM maintains a desired air/fuel ratio at precisely 14.7 to

1. To maintain a 14.7 to 1 air fuel ratio the PCM monitors the output signal from the oxygen sensor. The PCM will

either add or subtract fuel pulses based on the oxygen sensor output signal. This method of "feed back" fuel control

is called CLOSED LOOP.

In addition to fuel control, the PCM also controls the following systems:

• The ignition dwell

• The ignition timing

• The idle speed

• The engine electric cooling fan

• The electric fuel pump

• The instrument panel "Check Powertrain" lamp

• The A/C compressor clutch

• The automatic transmission functions

The PCM also interfaces with other vehicle control modules, such as the trip computer, the body control module and

the theft deterrent system. Figure 6C2-1-1 contains a list of the various operating conditions sensed by the PCM on

the left, and the various systems controlled on the right. Details of basic operation, diagnosis, and service are

covered in this CD-ROM.

The PCM has a built-in diagnostic system that identifies operational problems and alerts the driver by illuminating

the "Check Powertrain" lamp on the instrument panel. If the lamp comes "ON" while driving, it does not mean that

the engine should be stopped immediately, but the cause of the lamp coming "ON" should be checked as soon as is

reasonably possible. The PCM has built in backup systems that in all but the most severe faults will allow the

vehicle to operate in a near normal manner until repairs can be made.

Below the instrument panel to the left of the steering column is a Data Link Connector (DLC) which is used by the

assembly plant for a computer "check-out" of the PCM system. The DLC is also used in service to help diagnose

the system. Refer to Section 6C2-2, DIAGNOSIS for further details.

The locations of the main components of the system are shown in Figs. 6C2-1-3 through 6C2-1-6. For the

Transmission Management System Components and their locations, refer to Fig. 6C2-1-43.

Techline

Figure 6C2-1-1 PCM Operating Conditions Sensed and Systems Controlled

Figure 6C2-1-2 Powertrain Control Module System

Figure 6C2-1-3 Component Locations 5.0L V-8

Figure 6C2-1-4 V8 Engine View

Figure 6C2-1-5 V8 Engine View

Figure 6C2-1-6 Power Distribution Centre

1.1 POWERTRAIN CONTROL MODULE (PCM)

The Powertrain Control Module (PCM), is the

control centre of the fuel injection system, the

ignition system, and the automatic transmission

management systems. The PCM constantly

monitor s information f rom the var ious sensors, and

controls the systems that affect exhaust emissions

and vehicle performance. The PCM also performs

the diagnostic function of the system. The PCM can

recognise operational problems, alert the driver

through a Malfunction Indicator Lam p (MIL) “Check

Powertrain” lamp and store a diagnostic code(s)

which will identify problem areas to aid the

technician in making repairs. Refer to

Section 6C2-2, DIAGNOSIS for more information

on using the diagnostic functions of the PCM.

The PCM supplies either a buffered 5V or a

buffered 12V to power various sensors and

switches.

The PCM controls the output circuit of the fuel

injectors , the IAC valve, and the various r elays, etc.

The PCM controls the earth circuit through either

transistors or a device called a “quad-driver. The

two exceptions to this are the fuel pump relay

control circuit and if the vehicle has an automatic

transmission, the pressure control solenoid .

On vehicles equipped with an automatic

transmission, the PCM supplies current to the

pressur e control solenoid. T he PCM then m onitors

the amount of current that is returned to the PCM.

Figure 6C2-1-7 PCM Location

PCM SECURITY LINK

Once the PCM and or BCM have been replaced,

the new PCM and or BCM must be security linked

to each other. If this procedure is not performed,

the vehicle will not crank.

There are two different types of procedures that

may be performed to accomplish this task. Refer to

Section 6C2-3 SERVICE OPERATIONS for this

procedure.

PROM

To allow one series of a PCM to be used for many

different vehicles, a PROM is used. The PROM is

located inside the PCM. The PROM has

information on the vehicle's weight, engine,

transmission, axle ratio and several other factors.

While one PCM part number m ay be used by m any

different vehicles, a PROM is specific. Check the

latest parts catalogue and Service Techline

information for the correct part number when

replacing a PROM. A replacement PCM (called a

controller) is supplied without a PROM. T he PROM

from the old PCM must be carefully removed and

installed in the new PCM. For details, refer

Section 6C2-3, SERVICE OPERATIONS.

Figure 6C2-1-8 PCM PROM Location

PCM MEMORY FUNCTIONS

The following list contain the five types of memory

within the PCM:

ROM

RAM

PROM

EPROM

EEPROM

ROM

Read Only Memory (ROM) is a permanent memory

that is soldered to the circuit boards within the PCM.

The ROM contains the overall control algorithms.

Once the ROM is programmed, the program cannot

be changed. The ROM memory is non volatile, and

does not need power to be retained.

RAM

Random Access Memory (RAM) is the

microprocessor scratch pad. The processor can

write into, or read from this memory as needed. This

memory is volatile and needs a constant supply of

B+ voltage to be retained. If the B+ voltage is lost,

the memory is lost.

PROM

The Programmable Read Only Memory (PROM) is

the portion of the PCM that contains the different

engine and transmission calibration that is specific to

the year, the model and the emissions. The PROM is

a non volatile memory that is read only by the PCM.

The PROM is contained within the Memory

Calibration assembly and is removable from the

PCM. The PROM should be retained with the vehicle

following PCM replacement.

EPROM

Erasable Programmable Read Only Memory

(EPROM) is the portion of the PCM which means

that the program can be erased. This type of

memory is used to store the diagnostic trouble

codes. This memory is erased by disconnecting the

constant battery feed to the PCM, such as

disconnecting the battery.

EEPROM

Electronically Erasable Programmable Read Only

Memory (EEPROM) is the portion of the PCM

memory that the program can only be erased

electronically. This type of memory cannot be erased

by disconnecting the vehicle battery. The only way to

erase this type of memory is by a special electronic

tool. DTC history data is stored in EEPROM and will

be saved even after the B+ supply has been

disconnected. The only way that the DTC history

data can be cleared is with the Tech 2 scan tool.

1.2 ENGINE INFORMATION SENSORS

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

The Engine Coolant Temperature (ECT) sensor is

a thermistor (a resistor that changes value based

on temperature) mounted in the engine coolant

stream. A different sensor is used for instrument

panel functions.

A Low coolant engine temperature will produce a

high sensor resistance (28,939 ohms at -20

degrees C). A high engine coolant tem perature will

cause a low sensor resistance (180 ohms at 100

degrees C).

Figure 6C2-1-9 ECT Sensor

The PCM:

• Supplies a 5 volt ref erence voltage and an earth

to the ECT sensor.

• Supplies an earth circuit to the ECT sensor.

• Monitors the circuit voltage.

The circuit voltage will vary depending on the

resistance of the engine coolant temperature

sensor. The circuit voltage will be close to the 5

volts when the sensor is cold, and the resistance

will decrease as the sensor gets warmer. The

engine coolant temperature affects most systems

controlled by the PCM.

Figure 6C2-1-10 ECT Sensor Location

The PCM uses a duel pull-up resistor network to

increase the resolution through the entire range of

the engine coolant tem peratures. When the coolant

temper atur e is less than 51°C, both a 4k ohm and a

348 ohm resistor is used. When the coolant

temperature reaches 51°C, the PCM shorts the 4K

ohm resistor and only the 348K ohm resistor is

used. A fault in one of these two resistors will set

DTC 17.

A fault in the engine coolant temperature sensor

circuit should set either a Diagnostic Trouble Code

(DTC) 14 or DTC 15. An intermittent open or an

intermittent short fault should set a DTC 16.

Figure 6C2-1-11 ECT Temperature vs Voltage

LH AND RH HEATED EXHAUST GAS OXYGEN SENSORS

The heated exhaust gas oxygen sensors are the

key to closed-loop fuel control. The PCM uses

feedback voltage from the oxygen sensors to fine-

tune the fuel injector pulse width. The O2 sensor

voltage is based on the, oxygen content in the

exhaust.

The oxygen sensors that are used are heated.

When the ignition is turned to the ON position, B+

voltage is supplied to the sensor's heating element.

The O 2 sensor will than im mediately begin to warm

up. This reduces the time for the sensor to go into

closed loop.

The oxygen sensor contains a zirconia element.

When the zirconia is heated to temperatures

greater than 360 degrees C, the O2 sensor will

produce voltages based on the amount of oxygen

surrounding the tip.

Figure 6C2-1-12 Oxygen Sensor Location

The oxygen sensor is mounted in the exhaust pipe

with the sensing portion exposed to the exhaust

gas stream. When the sensor has reached a

temper ature of greater than 360 degrees C, the O2

sensor acts like a voltage generator. The O2

sensor begins pr oducing a r apidly changing voltage

between 10 and 1000 millivolts. T his voltage output

is dependent upon the oxygen content in the

exhaust gas, as compared to the sensor's

atmospheric oxygen reference cavity. The O2

sensor receives a reference air supply from the air

that passes between the wire strands and the

insulation.

W hen the oxygen sensor is cold, the O2 sensor will

produce either no voltage, or an unusable, slowly

changing voltage. As the oxygen sensor begins

heating, the internal resis tance of the O2 decreas es

and begins producing a rapidly changing voltage.

When the PCM senses the changing voltage, the

PCM knows the oxygen sensor is hot and the

sensor's output is ready to be used for the fine-

tuning the fuel injector pulse width. The PCM

monitors the oxygen sensors cycling band

(approximately 300 - 600 millivolts), to help

calculate when to operate in the closed-loop mode.

When the fuel system is operating in the closed-

loop mode, the oxygen sensor voltage is rapidly

changing several tim es per second. T he O2 sensor

voltage cycles above and below a rich/lean band.

The PCM monitors the changing voltage, and

calculates the needed fuel mixture correction.

A DTC 13 or a DTC 63 can be c aus ed by any of the

following conditions.

• An open oxygen sensor signal circuit.

• An open oxygen sensor earth circuit.

• A defective, contaminated, or cold oxygen

sensor.

Any one of these conditions could cause the

voltage to stay between 410 - 470 millivolt too

long. Keeping the fuel control system in open-loop.

Figure 6C2-13 Oxygen Sensor Zirconia Element

If the PCM monitors a low voltage for too long, a Diagnostic Trouble Code 44 or a DTC 64 will set. If the PCM

monitors a high oxygen sensor circuit voltage for too long, a DTC 45 or a DTC 65 will set. (refer to DTC 44 and

DTC 45).

The oxygen sensor is normally earthed through the oxygen sensor threads. The oxygen sensor is located in the

exhaust pipe. The oxygen sensor earth path may not remain a good earth because of corrosion problems and a

possible poor electrical earth path through the exhaust pipe and the exhaust manifold to the engine earth. The

oxygen sensor has an extra earth circuit to ensure a good earth. A wire is attached to the oxygen sensor housing

and the other end is attached to engine earth. The oxy gen sensor earth from the PCM is also attached to engine

earth, therefore, the earth path is complete between the oxygen sensor and the PCM.

RESPONSE TIME

Not only is it necessary for the oxygen sensor to produce a voltage signal for a rich or a lean exhaust, it is also

important to respond quickly to changes. The PCM monitors the response time. If the oxygen sensor responds

slowly, the customer may complain of poor fuel economy, rough idle or lack of performance. It may also set false

DTCs because the PCM uses oxygen sensor voltages for system checks.

OXYGEN SENSOR CONTAMINANTS

CARBON

Carbon or soot deposits results from an extremely rich air-fuel mixtures. Carbon does not harm an O2 sensor.

Deposits can be burned off in the vehicle by running the engine at least part throttle for two minutes.

SILICA

Certain RTV silicone gasket materials give off vapours that may contaminate the oxygen sensor. The sand like

particles from the RTV silica embed themselves in the oxygen sensor element and plug the surface. This will result

in a lazy oxygen sensor response time. The sensor will also have a whitish appearance.

Silica contamination can also be caused by silicone in the fuel. Careless fuel handling practices with the transport

containers can result in unacceptable concentrations of silicone in the fuel at the fuel pump.

There is also a possibility of silica contamination caused when installing vacuum hoses or fittings. Do not use

silicone sealers on the gaskets or the exhaust joints.

LEAD

Lead glazing of the oxygen sensor can occur when regular, or leaded fuel is burned. Fuel containing large amounts

of methanol will also result in lead contamination.

The methanol dissolves the terne coat of the fuel tank, which introduces lead into the fuel system, and into the

exhaust after combustion. Lead contamination is difficult to detect by visual inspection.

OTHER SUBSTANCES

Oil deposits will ultimately prevent oxygen sensor operation. The O2 sensor will have a dark brown appearance.

Causes of high oil consumption should be checked. The additives in ethylene glycol can also affect the oxygen

sensor performance.

This produces a whitish appearance. If antifreeze enters the exhaust system, you will likely encounter other, more

obvious, symptoms of cooling system trouble.

MULTIPLE FAULTS

If you encounter multiple or repeat oxygen sensor faults on the same vehicle, consider contamination.

Leaded fuel, silica contamination from uncured, low-grade (non approved) RTV sealant, and high oil consumption

are possible.

A problem in the oxygen sensor circuit or fuel system should set one of the following DTC(s)

• DTC 13 or a DTC 63 (open circuit)

• DTC 44 or a DTC 64 (lean indication)

• DTC 45 or a DTC 65 (rich indication)

Refer to applicable diagnostic chart if any of these DTCs are stored in memory.

Figure 6C2-1-14 Oxygen Sensor Voltage Curves

Figure 6C2-1-15 Normal Oxygen Sensor Voltages and Abnormal Trends

Figure 6C2-1-16 PCM Oxygen Sensor Circuitry

INTAKE AIR TEMPERATURE (IAT) SENSOR

The Intake Air Temperature (IAT) sensor is a

thermistor (a resistor that changes resistance with

changes in temperature). The IAT sensor is

mounted in the air cleaner housing.

The PCM supplies a 5V reference circuit and an

earth circuit to the sensor. A low intake air

temperature will produce a high resistance in the

sensor (100,000 ohms at -40 degrees C), while a

high air intake temperature will produce a low

sensor resistance (70 ohms at 130 degrees C).

Figure 6C2-1-17 IAT Sensor

The circuit voltage will vary depending on the

resistance of the IAT sensor. The voltage will be

close to 5-volts when the sensor is cold, and the

voltage will decrease as the sensor warms.

When the intake air is cold, such as when the

engine is firs t started on a cold day, the IAT s ensor

resistance will be high. Therefore the PCM voltage

signal will be, approximately 4 - 5 volts.

As the incoming air becomes warmer due to the

increasing engine temperature, the IAT sensor

resistance decreases, and the voltage will be

between 1 and 2 volts.

The IAT sensor signal voltage is one of the

param eters used by the PCM in calculating the fuel

injector pulse width.

A fault in the IAT sensor circuit should set either a

Diagnostic Trouble Code (DTC) 23 or a DTC 25.

An interm ittent fault in the IAT sensor cir cuit should

set a DTC 26. Figure 6C2-1-18 IAT Sensor Location

Figure 6C2-1-19 PCM IAT Sensor Circuit

MASS AIR FLOW (MAF) SENSOR

The Mass Air Flow (MAF) sensor used on this

engine utilises a heated elem ent. A heated elem ent

in the MAF sensor is placed in the air flow stream

of the engine intake air system. The heating

element is maintained at a constant temperature

above the ambient air temperature. The amount of

current required to maintain the heated element at

the ambient temperature is a direct function of the

mass flow rate of the air over the heated element.

Figure 6C2-1-20 Mass Air Flow Sensor

Three sensing elements are used in this system.

One senses the ambient air temper ature. The other

two sensing elements are heat sensing elements.

The ambient air temperature sensor is mounted in

the lower half of the sensor housing.

The two heater sensing elements are heated to a

calculated temperature that is significantly above

the ambient air temperature. The two heater

sensing elements are connected electrically in

parallel and mounted directly in the air flow stream

of the sens or housing. O ne sensor is in the top and

the other sensor is in the bottom of the sensor

housing. This is done so that the air meter is less

sensitive to upstream ducting configurations that

could skew the flow of air through the housing.

Figure 6C2-1-21 Sensing Elements

As the air passes over the heater sensing

elements, the elements begin to cool. By

measuring the amount of voltage required to

maintain the heater sensing elements at the

calculated temperature above ambient, the

incoming air flow rate can be calculated.

After the mass air flow sensor has developed a

signal related to the mass air flow rate, the MAF

sensor then sends the signal to the PCM. In order

to preserve the accuracy of the voltage signal from

the mass air flow sensor, the voltage is converted

to a frequency signal then sent to the PCM.

Figure 6C2-1-22 MAF Sensor Location

Figure 6C2-1-23 MAF Sensor Simplified Schematic

The signal that is sent from the mass air flow

sensor is sent in the form of a frequency output. A

large quantity of air passing through the sensor

(such as when accelerating) will be indicated as a

high frequency output. A small quantity of air

passing through the sensor will be indicated as a

low frequency output (such as when decelerating or

at idle). The scan tool displays the MAF sensor

signal in frequency, and in grams per second and

calculated in mg per cylinder. At idle the readings

should be low and increase with engine RPM.

As the PCM receives the fr equency s ignal from the

mass air flow sensor, the PCM searches the pre-

program med tables of inform ation to determine the

pulse width of the fuel injectors required to match

the mass air flow signal.

If a fault occurs in the mass air flow sensor circuit,

the PCM will store a DTC. The PCM will turn ON

the "Check Powertrain" lam p, indicating a problem.

If this oc c urs , the PC M will calculate a default mas s

air flow signal based on the engine speed and the

throttle position sensor signal.

No field service adjustment is necessary or

possible with this mass air flow sensor.

A fault in the mass air f low s ensor c irc uit s hould set

a DTC 32. T his DTC indicates a fault in the circuit.

Use of the diagnostic chart will lead to either

repairing a wiring problem, replacing the PCM, or

replacing the MAF Sensor.

Figure 6C2-1-24 Mass Air Flow Sensor Identification

Figure 6C2-1-25 MAF Sensor Circuit

THROTTLE POSITION (TP) SENSOR

The T hr ottle Pos ition (TP) s ens or is mounted to the

throttle shaft on the throttle body. The T P sensor is

a potentiometer. The PCM supplies a 5 volt

referenc e and a earth circuit to the TP sens or. The

signal circuit connects from a sliding contact in the

TP sensor to the PCM. This allows the PCM to

measure the voltage from the TP sensor. As the

throttle is depressed, the output of the TP sensor

changes. At a clos ed throttle position, the output of

the TP sensor is below 1.25V. As the throttle valve

opens, the output increases. At a wide-open

throttle, the TP sensor output voltage should be

greater than 4 volts.

Figure 6C2-1-26 TP Sensor

By monitoring the output voltage from the TP

sensor, the PCM can determine the fuel injector’s

base pulse width.

A broken or loos e T P s ens or c an c ause inter mittent

bursts of fuel from the injectors, and an unstable

idle, because the PCM thinks the throttle is moving.

Figure 6C2-1-27 TP Sensor - Typical

The T P sensor is not adj ustable. There is not a s et

value for the TP sensor voltage at closed throttle.

The actual voltage at closed throttle can vary from

vehicle to vehicle due to tolerances. The PCM has

a special program built in that can adjust for the

tolerance differences in the TP sensor voltage at

idle. The PCM uses the signal at idle for the zero

reading (0% throttle) so no adjustment is

necessary. If the TP sensor voltage were to

change, the TP sensor voltage will still be 0%

because the PCM will learn the new value. The

new value will become the new closed throttle

value. A TP s ensor c irc uit f ault will set either a DTC

21 or a DTC 22.

If the internal spring in the TP sensor fails, the TP

sensor will read high. A stuck high TP sensor

should set a DTC 19.

Figure 6C2-1-28 TP Sensor Location

Figure 6C2-1-29 PCM TP Sensor Circuit

VEHICLE SPEED SENSOR (VSS)

The vehicle speed sensor is located in the

transmission extension housing.

The vehicle speed sensor contains a coil that has

a continuous magnetic field. A voltage signal is

induced in the vehicle speed s ens or by teeth on the

output shaft that rotate past the sensor that break

the magnetic field. Eac h break in the field s ends an

electrical pulse to the PCM. T his voltage output will

vary with speed from a minimum of 0.5 volts AC at

100 RPM to more than 100 volts AC at 8000 RPM

on the vehicle. With the engine at 4000 RPM and in

fourth gear , the voltage will be approximately 10-12

volts AC.

Figure 6C2-1-30 VSS Location - Automatic Transmission

Figure 6C2-1-31 VSS Location - Manual Transmission

The PCM uses the signal from the vehicle speed

sensor to determine the following.

• The vehicle speed.

• The control shift points.

• Calculate transmission slip.

• The engine fuelling modes.

A Diagnostic Trouble Code 24 or DTC 94will set if a

fault exists in the vehicle speed sensor circuit. As

the vehicle is accelerated, the PCM will shift the

transmission into second gear at approximately 50

km/h. If the vehicle speed signal is not present

while in second gear, a DTC 24 will set. The PCM

will substitute a default value for the vehicle speed

if the fault occurred in fourth gear. If the fault

occurr ed in park, neutr al, or first gear , the PCM will

allow 1-2 shifts to occur. If a DTC 24 is set, then

the PCM will default into third gear. If the c onditions

for a DTC no longer exist, then normal operation

will resume after the next ignition cycle. Figure 6C2-1-32 Vehicle Speed Sensor

Figure 6C2-1-33 PCM VSS Circuit

A/C REQUEST SIGNAL

When the A/C is requested from the dash master A/C switch, the A/C request signal is sent to the BCM. The BCM

will then send a command via the serial data line to the PCM. The PCM will then supply a earth signal to the A/C

compressor relay, to energise the A/C compressor.

The PCM uses this BCM serial data command to:

• Adjust the Idle Air Control (IAC) position to compensate for the additional load placed on the engine by the air

conditioning compressor, and then

• Energises the A/C compressor relay, to operate the A/C compressor.

Figure 6C2-1-34 PCM A/C Request Signal Circuit Without ECC

Figure 6C2-1-35 PCM A/C Request Signal Circuit With ECC

BATTERY VOLTAGE

The PCM continually monitors the battery voltage. When the battery voltage is low, the ignition system may deliver a

weak spark. Also, the fuel injector mechanical movement takes longer to open. The PCM will compensate for a low

voltage condition by:

• Advancing the ignition timing whenever the battery voltage is less than 12 volts.

• Increasing the engine idle speed whenever the battery voltage is less than 10 volts.

• Increasing the fuel injector pulse width whenever the battery voltage is less than 10 volts.

Diagnostic Trouble Code (DTC) 53 will set when the ignition is ON and the PCM voltage is greater than 19.5 volts

for 2 seconds.

Diagnostic Trouble Code (DTC) 54 will set when the ignition is ON and the PCM voltage changes more than 3 volts

in less than 100 milliseconds.

The minimum voltage for DTC 75 to set is on a graduated scale. The scaling changes with temperature. A DTC 75

will set when the ignition is ON and the B+ voltage is less than the values listed below for about 4 seconds.

• Minimum voltage at -40 degrees C is 7.3 volts.

• Minimum voltage at 90 degrees C is 8.6 volts.

• Minimum voltage at 152 degrees C is 11.4 volts.

Figure 6C2-1-36 PCM Battery Feed

CRANKSHAFT REFERENCE SIGNAL

The crankshaft reference signal is generated within the distributor. The distributor contains a hall-effect crankshaft

sensor. This sensor acts as a reference voltage pulse generator. The crankshaft sensor provides the PCM with the

RPM and crankshaft positioning.

NOTE:

The engine will not run if the control module does not receive a crankshaft reference signal. With no distributor

reference signal the PCM will not command any fuel injector pulses.

The crankshaft reference signal initiates the fuel injector to fire. The PCM uses this signal to determine the engine

RPM. This is one of the signals used to control the following components or systems

• The Fuel Delivery

• The A/C Clutch (ON/OFF)

• The Electronic Spark Timing

• The Idle (IAC)

• The Transmission

Figure 6C2-1-37 PCM Ignition System Circuit

ENGINE COOLI NG FAN SIGNAL

LOW SPEED RESPONSE

The V8 engine has two, two speed electric cooling fans which provides the primary means of moving air through

the engine radiator. These fan are placed between the radiator and the engine and has its own shroud. These fan

are used on all vehicles whether or not it is equipped with air conditioning. There is no fan in front of the A/C

condenser.

The two, two speed electric fan's low speed can only be enabled when the engine cooling fan low speed relay is

energised by the BCM. The PCM will request low speed fan enable and disable via the serial communication to

the BCM. After the PCM requests a change in the engine cooling fan low speed relay , the BCM will send a serial

data response message back to the PCM confirming it received the message. A fault in this response

communication will set a DTC 92.

There are also four (4) suppression capacitors incorporated into the fan motor wiring circuits. These suppression

capacitors help eliminate fan motor noise through the radio speakers. If these capacitors are open, then noise will

be present through the radio speakers. Is shorted to earth, the fan motors could continuously run, or the fuse or

fusible link could fail.

Figure 6C2-1-38 Engine Cooling Fan Signal

ENGINE COOLING FAN HIGH SPEED

The engine cooling fan high speed is controlled by the PCM based on input from the Engine Coolant Temperature

Sensor (ECT). The PCM will only turn "ON" the engine cooling fan high speed if the engine cooling low speed fans

have been "ON" for 2 seconds and the following conditions are satisfied.

• There is a BCM message response fault which will cause a DTC 92.

• An engine coolant temperature sensor failure is detected, such as DTC 14,15,16,17.

• Coolant temperature greater than 109 degrees C.

If the fan low speed was "OFF" when the criteria was met to turn the fan high speed "ON", the fan high speed will

come "ON" 5 seconds after the fan low speed is turned "ON". The high speed engine cooling fan relay can also be

enable by the A/C Refrigerant Pressure Sensor. The A/C Refrigerant Pressure Sensor will enable high speed

cooling fan, if the A/C system pressure becomes to high.

If a fault occurs in the PCM Engine Cooling Fan Relay High Speed Control circuit, a QDSM DTC 91 will set.

There are also four (4) suppression capacitors incorporated into the fan motor wiring circuits. These suppression

capacitors help eliminate fan motor noise through the radio speakers. If these capacitors are open, then noise will

be present through the radio speakers. If shorted to earth, the fan motors could continuously run, or the fuse or

fusible link could fail.

TRANSMISSION FLUID PRESSURE (TFP) SWITCH ASSEMBLY

The Transmission Fluid Pressure (TFP) Switch Assembly is used by the PCM to sense what gear range has been

selected by the vehicle operator. The TFP is located on the transmission valve body and consists of five pressure

switches, 2 normally closed fluid pressure switches and 3 normally open fluid pressure switches combined into one

unit.

The Pressure Switch Assembly is one of the inputs used by the PCM to control Idle Air Control (IAC) and, the

transmission Operation.

Figure 6C2-1-39 Transmission Fluid Pressure (TFP) Switch Assembly Circuit

THEFT D ETERRENT INPUT SIGNAL

When the ignition switch is turned to the ON position, the BCM polls the PCM and sends an encrypted BCM/key

security code. The security code is received by the BCM, via the remote key reader (slip ring) or via the remote

receiver in the event of no slip ring communication.

The PCM compares the received security code with its stored security code and if matched, the PCM will continue

to enable fuel injector fuelling and engine crank.

The PCM will return a Valid Code message (OK TO START), which tells the BCM to jump from the short loop mode

to the long loop mode.

When the ignition os turned from the OFF position to the ON position, the BCM will communicate with the PCM for

antitheft purposes. If the BCM does not receive a message OK TO START from the PCM within 0.5 second of the

ignition being switched on, the auxiliary bus is isolated via switching within the BCM.

The isolation of the auxiliary data bus during this period eliminates the possibility of a device failure other than the

BCM or PCM causing a problem on the bus and inhibiting antitheft communications.

This period, known as ‘Short Loop Time’, continues until the PCM responds with an acknowledgment or a maximum

period of 5 seconds, after which the BCM will switch to the standard poling sequence.

Following successful antitheft communications, the BCM begins sequential polling of devices on the bus and normal

system operation is established.

Figure 6C2-1-40 Theft Deterrent System

Figure 6C2-1-41 PCM Theft Deterrent Serial Data Circuit

CAMSHAFT POSITION SIGNAL

The camshaft position sensor is located in the distributor directly under the cap. The camshaft position reference

signal is sent directly to the PCM. The PCM then calculates the position of the No. 1 cylinder on its power stroke.

This signal is used by the PCM to calculate sequential fuel injection operation. If the camshaft position signal is lost

while the engine is running, the fuel injection mode will be based on the last fuel injection pulse, and the engine will

continue to run. The engine can be restarted and will run in the synchronous (all eight injectors inject at once) mode

as long as the fault is present. When the camshaft position signal is not being received by the PCM, a DTC 48 will

set. An intermittent camshaft position signal will set a DTC 49. If either of these DTC's are set, the fuel system will

not be in the sequential fuel injection mode.

Figure 6C2-1-42 Camshaft Position Sensor Signal

1.3 TRANSMISSION INPUT INFORMATION SENSORS AND SIGNALS

The control module used with the Sequential Fuel Injection (SFI) engine is called a Powertrain Control Module

(PCM) and controls a number of engine functions such as.

• The fuel control

• The ignition timing

• The transmission functions

The diagnosis of this transmission requires the use of a Tech 2 scan tool.

The transmission control system part of the powertrain control module contains software and hardware. The

software and the hardware monitors a number of the engine and the vehicle functions. Then uses the data to

control the following operations.

• The torque converter clutch engagement.

• The upshift pattern.

• The downshift pattern.

• The line pressure to control shift quality.

INFORMATION SENSORS

The PCM uses the following information sensors and switches to gather data for electronically controlling the

transmission functions.

The Engine Coolant Temperature (ECT) sensor.

The Engine speed.

The Transmission Fluid Pressure Switch

Assembly.

The Throttle Position (TP) Sensor.

The Transmission Fluid Temperature (TFT) sensor.

The Transmission Economy/Power Switch.

The Vehicle Speed Sensor (VSS).

The Mass Air Flow (MAF) Sensor.

Figure 6C2-1-43 Transmission Electronic Component Location View

Figure 6C2-1-44 Transmission Wiring

TRANSMISSION FLUID PRESSURE (TFP) SWITCH ASSEMBLY

Figure 6C2-1-45 Transmission Fluid Pressure (TFP) Switch Assembly and Transmission Fluid Temperature Sensor

Figure 6C2-1-46 Transmission Fluid Pressure Switch Assembly (TFP) Switches

This gear range sensing device is called a

Transmission Fluid Pressure (TFP) switch

assembly. The TFP is used by the PCM to sense

what gear range has been selected by the vehicle

operator. The TFP is located on the valve body.

The TFP consists of five pressure switches. Two

normally closed and three normally open. The

normally open fluid pressure switches are the

"D4", "LO" and "Reverse" fluid pressure switches.

Electrical current is supplied to these switches

when fluid pressure is present. Fluid pressure

moves the diaphragm and contact element until

the contact element touches both the positive

contact and the earth contact. This creates a

closed circuit and allows current to flow from the

positive contact, through the switch to earth. The

normally closed fluid pressure switches are the

"D2" and "D3" fluid pressure switches. They are

norm ally closed and the electrical c urrent is free to

flow from the positive contact to the earth contact

when no fluid pressure is present. The fluid

pressure moves the diaphragm to disable the

positive and earth contacts. This opens the switch

and stops the current from flowing.

Figure 6C2-1-47 Transmission Fluid Pressure (TFP) Switch

Assembly

The PCM supplies the system voltage to the TFP

on three separate lines. An open circuit m easures

12 volts while an earthed circuit measures 0 volts.

The switches are opened and closed by the fluid

pressures. The combination of switches which are

open and closed are used by the PCM to

determ ine actual valve position. The T FP however

cannot distinguish between park and neutral

because the monitored valve body pressures are

identical in both cases.

• L-This switch will have hydraulic pressure

applied to it in m anual 1st gear only and will be

closed.

• R-This switch will have hydraulic pressure

applied to it in reverse only and will be closed.

• D2-This switch will have hydraulic pressure

applied to it in manual 1st and 2nd gear and will

be open.

• D3-This switch will have hydraulic pressure

applied to it in manual 1st, 2nd and 3rd gear

and will be open.

• D4-This switch will have hydraulic pressure

applied to it in all the drive gears except

reverse and will be closed.

Figure 6C2-1-48 Pressure Applied to TFP Switches

Use a high impedance digital volt ohm meter when

measuring the TFP voltages. Measure the TFP

voltage by backprobing the PCM then taking

readings from each terminal to earth. Then

compare these readings to the combination chart.

On the transmission wiring harness, pin N is

"Range Signal A", pin R is "Range Signal B", and

pin P is "Range Signal C". W ith the wiring harness

connected and engine idling, a voltage reading on

these three cir cuits will be B+ whenever the circ uit

is open. The circuits s hould read 0V whenever the

circuit is earthed.

These TFP inputs are used to help control the

following

• The line pressure

• The torque converter clutch apply

• The shift solenoid operation

To monitor the TFP assembly operation, the PCM

compares the actual voltage combination of the

switches to a TFP combination chart stored in

memory. If the PCM detects one of two "illegal"

voltage combinations a Diagnostic Trouble Code

28 will set.

There are two possible combinations of the

switches within the pressure switch assembly that

do not represent an actual gear range. If either of

these combinations are detected by the PCM, a

DTC 28 will set. A DTC 28 will not set if a valid

gear range combination appears at the wrong

time.

Figure 6C2-1-49 Transmission Fluid Pressure Chart

While a DTC 28 is present, the PCM will take the

following actions:

• Assume D4 for shift pattern control.

• Use the D2 pressure table.

• Inhibit the 4th gear operation in hot mode only.

• Inhibit the TCC operation.

• Turn the TCC ON in hot mode.

If the TFP resumes normal functioning, the

transm ission will resum e norm al operation after the

next ignition cycle.

A DTC 28 will not detect an open in either range

signal "B" or range signal "C". An open in either of

these signals will not be an illegal T FP com bination

but a legal TFP c om bination at the wrong tim e. T he

PCM will then receive the wrong information.

There are two faults in the TFP that will cause an

unusual complaint. If the range signal "B" is open

the PCM will interpret this PRNDL select as "2" in

park or neutral with the ignition "ON" or engine

idling. The customer will probably complain that

when "D" range is selected the transmission never

shifts into 4th gear. This is because the PCM only

control shif ts in "D" range, but because of the open

in range signal "B" the PCM interprets "3" and the

transm ission will never shift to f ourth gear because

this "3" input is a normal condition.

The other condition to cause an unusual complaint

is an open in the range signal "C". When the dr iver

selects range "3" the PCM will only interpret this

PRNDL select as "2" and will have 1st and 2nd

gears. If the driver selects "D" the transm ission will

have all gears and TCC but the Tech 2 scan tool

will read P-N all the time. Figure 6C2-1-50 Transmission Fluid Pressure (TFP) Switch

Assembly Location

Figure 6C2-1-51 Transmission Fluid Pressure (TFP) Switch Assembly

Figure 6C2-1-52 Transmission Fluid Pressure (TFP) Switch Assembly Switch Voltages

TRANSMISSION FLUID TEMPERATURE (TFT) SENSOR

The Transm ission Fluid Temperature (T FT) sensor

is a thermistor (a res istor that changes value based

temperature) that is part of the transmission fluid

Pressure (TFP) Switch Assembly Low transmission

fluid temperature produces high resistance and

high transmission fluid temperature produces low

resistanc e. The PCM supplies a 5 volt s ignal to the

Transmission Fluid Temperature (TFT) sensor

through an internal resistor then measures the

voltage drop in the circuit. The voltage will be high

when the transmission fluid is cold, and low when

the transmission fluid is hot.

Figure 6C2-1-53 TFT Sensor Temperature to Resistance

Relationship

The PCM uses the Transmission Fluid

Temperature (TFT) Sensor to regulate the torque

converter clutch apply, as well as the shift quality.

A Diagnostic Trouble Code (DTC) 58 and DTC 59

indicates a fault in the Transmission Fluid

Temperatur e (T FT) sensor c irc uit. T he Tech 2 s c an

tool will display the transmission fluid temperature

in degrees Celsius. After the vehicle has been

started, the transmission fluid temperature should

rise steadily and then stabilise between 90 and 115

degrees C, depending on load. Both diagnostic

trouble codes will cause the PCM to use a default

value of 130 degrees C. Thus reacting as if the

transmission were hot in either case. When

Diagnostic Trouble Code (DTC) 58 or DTC 59 are

set the torque converter clutch will be enabled in

third and fourth gear and will apply early. Some

driveability symptoms will be noticed especially

when cold.

A DTC 79 will set if the transmission fluid

temperature exceeds 146 degrees C and does not

go lower than 137 degrees C for 30 minutes. The

PCM monitor s the T F T s ens or f or determining DT C

79. An electrical fault in the TFT sensor circuit will

not set a DTC 79. A D TC 79 will only set if the fluid

actually did exceed the temperature or if the TFT

sensor is skewed high or stuck above the

temperature threshold.

Figure 6C2-1-54 Transmission Fluid Temperature Sensor

THROTTLE POSITION (TP) SENSOR

The TP sensor information is used for the engine

functions as well as for the autom atic transm ission

functions

TRANSMISSION ECONOMY/POWER SWITCH

The economy/power switch is used to modify

upshifts and shift times. The driver can select one

of the two transmission modes, "Economy" or

"Power" with a dash or centre console mounted

switch. The out position enables the power mode.

A green indicator lamp is located on the right side

of the instrument panel cluster and displays

"PWR" when illuminated to inform the driver that

the "Power" mode is now enabled.

The PCM sends a voltage signal, about 12 volts,

and monitors the status of this circuit. In the

"Economy" position, the switch is open and the

PCM voltage status signal remains high, about 12

volts. The PCM does not allow shift point changes

in the economy mode. When the transmission

switch is pressed to the Power position the switch

is closed and the PCM voltage status signal is

pulled low, about 0.5 volts. The PCM senses this

voltage drop and enables Power mode (alternate

shift pattern 'tables' to be utilised).

In the "Power" mode, the TCC can be applied in

3rd and 4th gears. When the TCC is applied in 3rd

gear it will stay applied until the normal 4th gear

upshift criteria is met. When the 3-4 upshift

occurs, the TCC will be released momentarily.

Also, in the "Power" mode while in "D" gear select

position, the PCM will delay the 1-2 and 2-3 shift

while under light throttle. The shift patterns will be

the same in the "Economy" and "Power" modes if

the TP sensor is between 80% - 100%. The power

mode should be used when towing as applying the

TCC in 3rd and 4th gear reduces slippage in the

TCC and thus reduces heat build up.

Figure 6C2-1-55 Transmission Economy/Power Switch

Figure 6C2-1-56 Transmission Economy/Power Switch Wiring

VEHICLE SPEED SENSOR (VSS)

The VSS information is also used for engine functions as well as for the transmission management system. For

VSS information, refer to 1.2 ENGINE INFORMATION AND SENSORS in this Section.

TRANSMISSION PASS-THRU CONNECTOR

The transmission electrical pass-thru connector is a

very important part of the HYDRA-MATIC 4L60-E

operating system.

The wiring harness electric ally c onnects the PCM to

the various sens ors, s olenoids, and relays within the

transmission management system. Many of the

connectors used are environmentally protected. This

is because of the systems low voltages and low

current levels. Anything that interferes with the

electrical connection can cause the transmission to

set diagnostic trouble codes and/or operate

incorrectly.

The following conditions can affect proper electrical

connections.

• Bent pins in the connector from rough handling

during connecting and disconnecting.

• Wires backing away from the pins or coming

uncrimped (in either the transmission or

powertrain wiring harness).

• Dirt contamination entering the connector after

the connector is disconnected.

• Pins in the connector backing out of the

connector or pushed out during connection.

• Excessive transmission fluid leaking into the

connector, wicking up into the powertrain wiring

harness and degrading the wire insulation.

• Water/moisture intrusion in the connector.

• Low pin tension from excessive connecting and

disconnecting of the wiring harness.

• Pin corrosion from contamination.

The presence of transmission fluid in the

transm iss ion connector is not harm ful. T he f luid only

affects the vehicle harness wiring insulation if the

fluid wicks up.

Points to remember when working with the

transmission electrical connector.

• To remove the connector, squeeze the two tabs

towards each other and pull straight up.

• Limit the twisting or the wiggling of the connec tor

during removal.

• Do not pry the connector with a screwdriver or

any other tool.

• To install the connector, first orient the pins by

lining up the arrows on each half of the

connector. Pus h the connector straight down into

the transmission without twisting or angling the

mating parts.

• The connector should click into place with a

positive feel and/or noise.

• Whenever the transmission pass-thru connector

is disconnected from the transmission, and the

ignition is switched is ON or the engine is started,

numerous DTC's will set.

Figure 6C2-1-57 YB 129 Powertrain Harness Connector

1.4 TRANSMISSION OUTP UTS CONTROLLED BY THE PCM

PRESSURE CONTROL SOLENOID

The transm ission Pressure Control Solenoid (PCS)

is an electronic pressure regulator that controls

pressure based on current flow through its coil

winding. The magnetic field produced by the coil

moves the solenoid's internal valve which varies

the pressure to the pressure regulator valve.

Figure 6C2-1-58 Pressure Control Solenoid

The pressure control solenoid takes the place of

the throttle valve used on past model 4L60

transmissions. The PCM varies the line pressure

based on engine load. Engine load is calculated

from various inputs, including the TP sensor and

the MAF sensor. The transmission’s line pressure

is regulated by the PCM. The PCM controls the

amperage applied to the pressure control solenoid

between 0 amps (high line pressure) to 1.1 amps

(low line pressure). This changes the duty cycle of

the pressure control solenoid, which ranges

between 0% to 100%.

Diagnostic T rouble Code 73 will set when the PCM

detects a difference of 0.16 amp or more between

the amperage commanded and actual amperage.

When a DTC 73 is set, the pressure control

solenoid will be commanded OFF creating

maximum line pressure. Whenever the conditions

for setting the DTC no longer exist the PCM will

then resume the normal operation of the pressure

control solenoid. Figure 6C2-1-59 Pressure Control Solenoid Cutawa y View

SHIFT SOLENOIDS

The 1-2 s hif t s olenoid and the 2- 3 s hif t s olenoid are

identical solenoids in operation that control the

movement of the 1-2 and 2-3 shift valves (the 3-4

shift valve is not directly controlled by a shift

solenoid). The solenoids are normally open valves

that work in four combinations to shift the

transmission into different gears. The PCM

controlled sh ift solenoids elim inate the need for the

Throttle Valve and the governor pressures to

control shift the valve operation.

IMPORTANT:

The PCM does not have total contr ol of shifting the

transmission. The manual valve can hydraulically

override the shift solenoids. Only in "D" are the

PCM and shift solenoids totally determining what

gear the transm ission is in. In the m anual positions

"3", "2", and "1", the transmission manual valve

position will change fluid direc tion in the valve body.

The transmission will shift hydraulically. The PCM

will have limited control and will respond to the

hydraulic changes to the manual valve. The PCM

will change the shift solenoids when the pressure

switch assembly switches change position and

throttle position and vehicle speeds fall into the

correct ranges for PCM control. In other words the

PCM "catches up" to what happened hydraulically.

The Tech 2 scan tool will only display the

commanded state of the shift solenoids not the

actual gear the transmission is in.

Figure 6C2-1-60 Shift Solenoids

Figure 6C2-1-61 Shift Solenoid Valve Cutaway View

Figure 6C2-1-62 Solenoid Status

1-2 SHIFT SOLENOID

The 1-2 s hift solenoid is attac hed to the valve body

and is a normally open valve. The PCM enables the

solenoid by earthing it through an internal quad

driver. The 1-2 shift solenoid is ON in 1st and 4th

gear, and OFF in 2nd and 3rd gears.

When ON, the shift solenoid redirects the fluid to

act on the shift valves.

There is one diagnostic trouble code associated

with the 1-2 shift solenoid, Diagnos tic T r ouble Code

82 1-2 shift solenoid circuit fault. The PCM

continually monitors the 1- 2 shif t s olenoid cir cuit f or

expected voltage (O FF high ON low). If the voltage

reading is not what is expected on the circuit, a

DTC 82 will set. While Diagnos tic Trouble Code 82

is set, the line pr essure will be high and the vehicle

will have 2nd or 3rd gear only. Whenever the

conditions for setting a DTC 82 no longer exist the

PCM will then resume normal operation of the 1-2

shift solenoid .

2-3 SHIFT SOLENOID

The 2-3 shift s olenoid is attached to the valve body

and is a normally open valve. The PCM enables the

solenoid by earthing it through an internal quad

driver. The 2-3 shift solenoid is ON in 1st and 2nd

gear and OFF in 3rd and 4th gear. When ON, the

shift solenoid redirects the fluid to act on the shift

valves.

There is one Diagnostic Trouble Code (DTC)

associated with the 2-3 shift solenoid DTC 81. T he

PCM continually monitors the 2-3 shift solenoid

circuit for expected voltage (OFF high ON low). If

the voltage reading is not what is expected,

Diagnostic T rouble Code 81 will set. W hile DTC 81

is set, the TCC operation will be inhibited, the line

pressure will be set to high and the transmission

will have 2nd or 3rd gear only. Whenever the

conditions for setting the DTC no longer exist the

PCM will then resume normal operation of the 2-3

Shift Solenoid on the next ignition cycle.

3-2 SHIFT SOLENOID

The 3-2 shift solenoid is a pulse width modulated

(PWM) solenoid used to im prove the 3-2 downshif t.

The 3-2 shift solenoid uses pulse width modulation

to control pressure so that the release of the 3-4

clutch and the apply of the 2-4 band are smooth.

The duty cycle is normally about 0% in first gear

and about 90% in all other drive gears, except

during a 3-2 downshift when the duty cycle drops.

The duty cycle is determined by the following

inputs.

• The throttle position

• The vehicle speed

• The commanded gear

Figure 6C2-1-63 3-2 Shift Solenoid

There is one Diagnostic Trouble Code (DTC)

associated with the 3-2 shift solenoid, DTC 66. A

DTC 66 will set when the PCM detects either A

high voltage when the 3-2 shift solenoid is

commanded high duty cycle or if low voltage exists

on the feedback line when the solenoid is

commanded low duty cycle. While the 3-2 shift

solenoid DT C 66 is s et, the s olenoid will be at a low

duty cycle, creating a soft shift into 3rd gear. The

vehicle will only have 3rd gear unless second gear

is manually selected. The torque converter clutch

will be ON in third gear only and the line pressure

will be high. Whenever the conditions for setting the

DTC no longer exist, the PCM will then resume

normal operation of the 3-2 shift solenoid on the

next ignition cycle.

Figure 6C2-1-64 3-2 Shift Solenoid Valve Cutaway View

TORQUE CONVERTER CLUTCH (TCC) SOLENOID VALVES

This transmission uses two Torque Converter

Clutch (TCC) solenoids. The torque converter

clutch solenoids are used to control torque

converter clutch apply and release. The TCC

enable solenoid has priority in applying and

releasing the torque converter clutch.

The Torque Converter Clutch (TCC) enable

solenoid is commanded either ON or OFF by the

PCM. When earthed (energised ON), by the PCM,

the TCC enable solenoid stops the converter feed

from exhausting. This causes the converter feed

pressur e to increase and shif t the TCC valve to the

apply position. This pressure allows the TCC to

couple the transmission with the engine for a near

100% engagement.

Figure 6C2-1-65 Torque Converter Clutch (TCC) Enable

Solenoid

There are two Diagnostic Trouble Codes (DTC)

associated with the TCC enable solenoid. The first

diagnostic trouble c ode is DTC 67, the T CC enable

Solenoid Circuit Fault. DTC 67 is designed to

detect a fault in the TCC electrical circuit. While a

DTC 67 is set the PCM will inhibit 4th gear if the

transmission is in the hot mode, and no TCC

operation.

The second diagnostic trouble code associated

with the TCC enable solenoid is DTC 69, TCC

Stuck ON. Diagnostic T rouble Code 69 is des igned

to detect a TCC that does not disengage. It does

this by monitoring engine RPM when the TCC

enable solenoid is commanded ON. If the engine

speed does not increase when the TCC enable

solenoid is disengaged, a DTC 69 will set. W hile a

DTC 69 is set the TCC will be ON in all gears or

second, third and fourth gears depending upon the

fault, and the transmission will have an early shift

pattern. Whenever the conditions for setting the

DTC no longer exis t, the PCM will then resum e the

normal operation of the TCC, on the next ignition

cycle.

Figure 6C2-1-66 TCC Solenoid Cutaway View

The Torque Converter Clutch "PWM" Solenoid is

used to control the fluid acting on the converter

clutch valve. This controls the TCC apply and the

release. This solenoid is attached to the control

valve body assembly within the transmission. The

TCC "PWM" Solenoid does not have total control

over the TCC engagement. The TCC PWM

Solenoid is used as a supplement to the TCC

enable Solenoid. The TCC "PWM" Solenoid is used

to provide smooth engagement of the torque

converter clutch by operating on a negative duty

cycle percent of ON time. This means that the

earth (negative or low) side of the solenoid circ uit is

controlled by the PCM.

Figure 6C2-1-67 Torque Converter Clutch (TCC) "PWM"

Solenoid

The TCC "PWM" solenoid is constantly fed B+ to

the high side. The PCM controls the length of time

the electrical c ircuit path to earth is closed (i.e. duty

cycle).

When the PCM closes the solenoid earth circuit,

current flows through the TCC "PWM" solenoid,

and the earth circuit is at a low voltage state (0

volts and solenoid energised).

Fig. 6C2-1-69 illustrates an example of the TCC

"PWM" solenoid operating with a 90% negative

duty cycle at a constant operating frequency of 32

Hz (cycles per second). The frequency means that

the solenoid is puls ed (energised) with current fr om

the PCM 32 times per second. The 90% negative

duty cycle means that during each of these 32

cycles the solenoid is energis ed (ON) and 0 volts is

measured on the low (negative) side of the circuit,

90 % of the time.

Figure 6C2-1-68 Torque Converter Clutch (TCC) "PWM"

Solenoid Cutaway View

At speeds below approximately 13 km/h, the

negative duty cycle will be 0%. This means that no

current will flow to the TCC "PW M" s olenoid, W hen

in this condition, the spring force will move the

plunger (refer Fig. 6C2-1-66), seating the metering

ball and blocking the filtered Actuator Feed Limit

(AFL) fluid from entering the Torque Converter

Clutch Signal (TCC SIGNAL) circuit. This action

opens the Torque Converter Clutch Signal fluid

circuit to exhaust through the solenoid.

Above the speed of approximately 13 km/h, the

TCC "PWM" solenoid will be operating at about a

90% duty cycle. T his action will cause the m etering

ball to close off the path to exhaust, most of the

time and allow fluid to flow past the metering ball

and into the TCC SIGNAL circuit, in readiness for

the apply of the torque converter clutch.

W hen the PCM signals the TCC to apply, the TCC

"PWM" solenoid operates with a variable, negative

duty cycle, ranging from 90% to 0%, with an

operating fr equency of 32 Hz. Th is allows the PCM

to control the current flow through the solenoid coil

according to the duty cycle that it sets . This has the

effect of creating a variable magnetic field, that

magnetises the solenoid core, attracting the

metering ball to seat against spring force. A high

percentage duty cycle keeps the metering ball

seated more, thereby creating higher TCC signal

fluid pressures.

Figure 6C2-1-69 Torque Converter Clutch (TCC) "PWM"

Solenoid Duty Cycle

TCC "PWM" SOLENOID OPERATION

W hen the vehic le road speed r ises above about 13

km/h, the PCM commands the TCC "PWM"

solenoid duty cycle to change from 0% to 90%, in

readiness for an apply of the torque converter.

To apply the torque converter clutch, the process

the PCM adopts, is as follows;

-The duty cycle is dropped to 0% (point "B")

and a measurable amount of time is allowed

for the T CC enable solenoid to turn "ON". This

is shown as the time between points "B" and

"C" in Fig. 6C2-1-67. Note that, at point "B",

the TCC enable solenoid is activated.

-The tim e from point "C" to "D" is used to allow

converter ( CONV FD) fluid to build in pressure

and move the Converter Clutch Valve into the

apply position.

-At this point, with the TCC enable solenoid

applied, the PCM increases the duty cycle to

about 26% (point "E"). From this point, the

duty cycle is 'ram ped' to around the 82% point

("E" to "F"). T he rate at which the duty cyc le is

increased over this period of time, determ ines

how quickly the value of the regulated apply

fluid increases and therefore, how quickly the

torque converter clutch is applied. This rate of

change also affects the converter clutch apply

'feel'.

-As soon as the duty cycle reaches 82%, it is

then immediately increased to the maximum of

90%, to achieve full apply pressure in the

regulated apply fluid circuit (point "G").

NOTE:

That the duty cycle and apply pressure will

continually vary, depending on vehicle specif ication

and operating conditions.

The two TCC solenoids work together so that the

TCC apply or release rate can be calibrated for a

variety of conditions.

If a fault is detected by the PCM, in the TCC

"PWM" solenoid electr ical cir cuit, a DT C 83 will set.

W hen a DTC 83 is set, the PCM will inhibit the 4th

gear operation and the TCC operation.

Figure 6C2-1-70 Torque Converter Clutch Solenoid

Operation

1.5 FUEL CONTROL SYSTEM

PURPOSE

The purpose of closed loop fuel control is to control the tailpipe emissions. The tailpipe emissions consist of

hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx).

The closed loop system regulates the exhaust emissions by controlling the air/fuel ratio at an optimum level during

various driving conditions. The most efficient air/fuel ratio to minimise exhaust emissions is 14.7 to 1. This allows

the three-way catalytic converter to operate at a maximum conversion efficiency. Due to the constant monitoring of

the exhaust gases by the oxygen sensor, and the adjusting of the fuel injector pulse width by the PCM, the fuel

injection system is called a "closed-loop" fuel control system.

FUNCTION

The fuel supply system delivers the fuel at a regulated pressure to the fuel rail. The fuel injectors, act as fuel flow

control valves. The fuel injectors spray atomised fuel into the inlet ports whenever they are "pulsed" by the PCM. All

VT vehicles are equipped with the sequential port fuel injection system.

The PCM controls the amount of fuel being injected into the engine by controlling the time the fuel injectors are

opened. This length-of-time is called a pulse width. To increase the amount of fuel being injected, the pulse width is

lengthened, and vice versa. The pulse width is calibratable and varies between 0 - 11 milliseconds with the engine

running at idle. The injection pulses normally occur once every crankshaft revolution.

MASS AIR FLOW SYSTEM

The Mass Air Flow sensor measures the intake air that enters the engine.

Advantages of Mass Air Flow.

• Will compensate for variations in base engine components. (Camshaft, valves, compression ratio)

• Compensates for engine aging.

• No air measurement lag time.

• Excellent idle stability.

Two specific data sensors provide the PCM with the basic information for the fuel management portion of operation.

That is, two specific signals; crankshaft reference signal from the ignition system, and the Mass Air Flow (MAF)

sensor signal. Both of these signals to the PCM establish the engine speed and amount of air entering into the

engine. Due to the additional temperature compensation sensor in the MAF sensor, this system does not require a

manifold absolute pressure sensor.

The engine RPM signal comes from the ignition module to the PCM on the crankshaft reference signal. The PCM

uses RPM information to calculate the fuel injector pulse width and the spark timing for a given operating RPM

band.

The amount of air entering into the engine is sent as a signal from the mass air flow sensor to the PCM.

When the engine is started, the PCM will immediately look at the Engine Coolant Temperature sensor to determine

how much fuel is required to start the engine. The PCM constantly monitors the MAF sensor values to determine

both the spark advance and the engine fuelling requirements. The Mass Air Flow sensor measures the amount of

air that enters into the engine. The PCM then calculates how much fuel that must be injected to maintain an air/fuel

ratio of 14.7 to 1. An engine started in cold weather will require more fuel and more spark advance than an engine

started hot.

The mass air flow sensor used on this engine utilises a heated element. Three sensing elements are used in this

system.

As the incoming air passes over the heated elements they begin to cool. By measuring the amount of voltage

required to maintain the heated elements at a temperature above ambient temperature the mass air flow rate can

be calculated.

As the PCM receives the frequency signal from the mass air flow sensor, the PCM searches for programmed tables

to determine the pulse width of the fuel injectors required to match the mass air flow signals.

The signal that is sent from the mass air flow sensor is sent in the form of a frequency output. A large quantity of air

passing through the sensor (such as when accelerating) will be indicated as a high frequency. A small quantity of air

passing through the sensor will be indicated as a low frequency (such as deceleration or at idle). The Tech 2 "scan"

tool displays the MAF sensor information in frequency, grams per second. A "normal" reading is approximately 6 -

10 grams per second at idle and increases the engine RPM.

MODES OF OPERATION

The PCM monitors the voltage signals from several of the sensors to determine how much fuel to deliver to the

engine. Also, when to operate in the open-loop or closed-loop mode. The fuel is controlled in one of several

possible modes. All the modes are controlled by the PCM, and are described in the following paragraphs.

STARTING MODE

When the ignition is turned ON, the PCM will energise the fuel pump relay. Then the fuel pump relay will energise

the fuel pump. The fuel pump then pressurise the fuel rail. The PCM then checks the engine coolant temperature

sensor to determine the injector pulse width for starting the engine.

When the cranking begins, the PCM will operate in the Starting Mode until the engine speed is greater than 400

RPM -or- the "Clear Flood" mode is enabled. The pulse width during the Starting Mode is between 4 and 26

milliseconds, depending on the engine coolant temperature.

CLEAR FLOOD MODE

If the engine floods, it can be started by depressing the accelerator pedal to the floor while cranking the engine. The

PCM then pulses the fuel injectors with only a 4 millisecond pulse width. This should clear a flooded engine. The

PCM holds this pulse width as long as the throttle position sensor indicates the throttle is nearly wide open, and

RPM is below 400.

If the throttle is held wide-open, while attempting to start a non-flooded engine, the engine may not start. A 4

millisecond pulse width may not be enough fuel to start a non-flooded engine, especially if the engine is cold.

NORMAL OPEN LOOP MODE

After the engine is running (RPM more than 400), the PCM will operate the fuel control system in the Open Loop

mode. In open loop, the PCM ignores the signal from the Oxygen Sensor (O2S), and calculates the air/fuel ratio

injector pulse width based on inputs from the crankshaft reference signal (RPM input) and these four sensors.

• The MAF sensor

• The IAT sensor

• The ECT sensor

• The TP sensor

The system will stay in the Open Loop mode until all the Closed Loop mode criteria have been met.

In open loop, the calculated pulse width may give an air/fuel ratio other than 14.7 to 1. An example of this would be

when the engine is cold, because a richer mixture is needed to ensure good driveability.

The normal open loop mode is not active when adverse or abnormal vehicle operating conditions are occurring

adverse conditions include engine overheating due to high vehicle speed or high ambient temperature.

RUN CLOSED LOOP MODE

In the Closed Loop mode, the PCM initially calculates the fuel injector pulse width with the same sensors it uses in

open loop. The difference is that in closed loop, the PCM uses the Oxygen Sensor signal to modify and precisely

tune the fuel. in order to precisely maintain the 14.7 to 1 air/fuel ratio. This allows the catalytic converter to operate

at it's maximum conversion efficiency.

IDLE MODE

The Idle Mode allows a slightly richer mixture at idle for better idle quality. The Idle Mode air/fuel ratio is about 14

to 1. This is an open loop mode, meaning the O2 sensor signal is ignored.

The Idle Mode is in when the throttle is closed, and the vehicle speed is less than 5 km/h.

In the case where the vehicle comes to a stop while operating in the Closed Loop mode, the Idle Mode will be

delayed for about 20-30 seconds. During this time, the PCM will "learn" a fuel correction factor for a 14.7 to 1 air/fuel

ratio before switching to the Idle Mode.

ACCELERATION MODE

The PCM looks at rapid changes in throttle position (TP sensor) to increase engine power, and provides extra fuel

by increasing the injector pulse width. If the increased fuel requirements are great enough, the PCM may add extra

fuel injection pulses between the injector pulses that normally occur once per crankshaft revolution.

DECELERATION MODE

When deceleration occurs, the fuel remaining in the intake manifold can cause excessive emissions and possibly

backfiring. The PCM monitors the changes in throttle position, and air flow, then reduces the amount of fuel being

delivered by decreasing the pulse width.

DECEL FUEL CUTOFF MODE

Decel fuel cutoff disables the fuel delivery during a deceleration to reduce the emissions and to improve the fuel

economy.

When deceleration from road speed occurs, the PCM can cut off the fuel pulses completely for short periods. The

decel fuel cutoff mode occurs when all of the following conditions are met:

• The Coolant temperature is above 63 degrees C.

• The Engine RPM has dropped more than 200 RPM.

• The Vehicle speed is greater than 42 km/h.

• The Throttle Position Sensor angle is less than 2%.

When the decel fuel cutoff is in effect, any one of these can cause the injection pulses to restart.

• The Engine speed has not dropped more than 200 RPM.

• The Vehicle speed is less than 42 km/h.

• The Throttle Position Sensor is greater than 2%.

BATTERY VOLTAGE CORRECTION MODE

At low battery voltages, the ignition system may deliver a weak spark. Also, the fuel injector will take longer to open.

The PCM will compensate by:

• Increasing the spark advance whenever the system voltage is less than 12 volts.

• Increasing the idle RPM whenever the system voltage is less than 10 volts.

• Increasing injector pulse width whenever the system voltage is less than 10 volts.

FUEL CUTOFF MODE

Fuel is cutoff by the PCM whenever the ignition is turned OFF. This prevents dieseling. Also, the fuel pulses are not

delivered if the PCM doesn’t receive any distributor reference pulses from the ignition module.

The Fuel Cutoff Mode is also enabled at

• High engine RPM, as an over speed protection for the engine. When cutoff is in effect due to high RPM, injection

pulses will resume after engine RPM drops slightly.

• High vehicle speed.- When the vehicle speed exceeds a calibratable value (about 220 km/h) the fuel base pulse

width is set to zero. Normal fuel operation will return when the vehicle speed falls below a calibratable value

(about 210 km/h).

SEQUENTIAL FUEL INJECTION MODE

When the engine is cranked, all eight injectors will be energised simultaneously. After the engine has been started

and a good camshaft signal has been processed, the PCM will energise each individual injector in the normal firing

order. This mode of operation helps to stabilise idle, reduce emissions and reduce fluctuations in fuel pressure

ADAPTIVE LEARNING

Adaptive learning is the ability of the on-board computer to determine and remember its most recent operating

experience. The PCM uses this remembered information to "learn from experience" and to make adjustments with

respect to what it learnt. If the engine were to develop a restricted fuel filter, the PCM will change the fuel injector

pulse width richer to compensate for this condition and will remember to keep this fuel injector pulse in memory until

the restriction is corrected. After the restriction has been fixed, the PCM will eventually go back to the original pre-

programmed fuel injector pulse.

Adaptive learning is an on-going process that continues throughout the life of the engine. A new engine with good

compression will have good vacuum. As the engine wears and compression decreases, a slight decrease in engine

vacuum will be noticed, which translates into a slightly lower MAF grams per second at idle, which will decrease

injector pulse width to compensate for this condition.

SHORT TERM FUEL TRIM

Short Term Fuel Trim (STFT) represents short term corrections to the fuel injector pulse width calculations, based

on the oxygen sensor input signal to the PCM.

When the engine is started cold, in "Open Loop," the PCM will control the fuel injection pulse width based upon

various sensor inputs such as RPM, ECT, MAF and TP sensor until the oxygen sensors become hot enough

(approximately 315 degrees C) to operate properly. During this "Open Loop" period, both Short Term Fuel Trim

(STFT) and Long Term Fuel Trim (LTFT) are disabled and will read 0% on a Tech 2 scan tool.

When the oxygen sensor has come up to its normal operating temperature (approximately 600 degrees C or

above), it will produce a varying voltage to the PCM and provide a good indication of what has happened in the

combustion chambers.

At this time the PCM will switch from "Open Loop" to "Closed Loop" and the STFT will start to constantly monitor the

oxygen sensor signal, so that the PCM can modify fuel injector pulse width wi th greater accuracy than in "Open

Loop".

STFT monitors the oxygen sensor signal so that it can adjust the fuel injector pulse width to maintain an air/fuel ratio

of 14.7 to 1 for maximum catalytic converter efficiency. An STFT value of 0% is equivalent to an air/fuel ratio of 14.7

to 1 and an average oxygen sensor signal voltage of 450 mV.

The normal position for Short Term Fuel Trim is 0%, any change from this value indicates the Short Term Fuel Trim

is changing the fuel injector pulse width. The amount of pulse width change depends upon how far the STFT value

is from 0%. If the STFT value is above 0%, the fuel injector pulse width is being increased, thus adding more fuel. If

the STFT value is below 0%, the fuel injector pulse width is being decreased, thus removing fuel. The normal

operating range of STFT is considered to be between -22% and +25% ; any value out of this range is usually

caused by a malfunction.

If an engine has a restricted fuel filter, the low fuel pressure will result in less fuel being injected and allows more air

into the air charge than is needed to ignite the amount of fuel the fuel injector has injected, therefore, a lean air/fuel

ratio exists in the combustion chamber. After combustion has taken place, the exhaust gases still contain more

oxygen content than normal and the oxygen sensor reads this as low voltage, say 200 mV. The STFT detects that

the oxygen sensor signal is low and will increase the value to richen up the air/fuel mixture. On a Tech 2 scan tool it

will display STFT as a value above 0%. This STFT change will increase the injector pulse width allowing the fuel

injectors to stay open longer and inject more fuel.

If the additional fuel was injected and the oxygen sensor signal voltage is still low, the STFT will continue to increase

its value until the oxygen sensor signal voltage goes above 450 mV. If the STFT continues to detect a low oxygen

sensor signal voltage it will continue to try and compensate for the lean exhaust condition until it runs out of its

authority in the particular Long Term Fuel Trim (LTFT) cell it's operating in. At this point, the PCM will reset STFT to

0% and go through this procedure again until it can control the system.

If after a specified amount of resets have been tried and failed, the PCM knows that it cannot control for the failure

and the STFT will remain at its maximum value.

STFT values are based on the oxygen sensor signal voltage reading, therefore, STFT is used by the PCM to make

quick changes to the fuel injector pulse width over a short period of time.

LONG TERM FUEL TRIM

Long Term Fuel Trim is used to adjust for engine to engine variation and to adjust for engine aging. LTFT is a

portion of the PCM memory used to adjust fuel delivery across all operating conditions of the engine. The PCM

monitors the STFT and will adjust the long term trend of the fuel injector pulse width if the STFT has been at a value

for a certain period of time. LTFT is used to change the long term fuel injector pulse width and is only operational

when the fuel control system is in "Closed Loop." A normal LTFT value is 0% and should follow the STFT value.

If an engine has a restricted fuel filter, the low fuel pressure will result in less fuel being injected and will cause the

STFT value to go higher than 0%, say 2%. If this STFT value change does not compensate for the restricted fuel

filter, the PCM will continue to increase the STFT value. The STFT may climb as high as its maximum calibrated

value if there is a severe restriction. The PCM will continue to monitor STFT as it climbs, but it will not make any

changes to the fuel injector pulse width for a specific period of time. After a specific period of time has elapsed and

the STFT value has remained above say +8%, the LTFT will move up to say 4% and wait again to detect if the

STFT has dropped back down to 0%. If not, the STFT will gradually move toward its maximum calibrated value limit

until it gains control of the fuel injection sy stem. If STFT and LTFT are both set at their maximum value limit, the

fuel control system is "out of the limits of control" and will set either a Diagnostic Trouble Code (DTC) 44, or DTC 64

(lean exhaust) or DTC 45, or DTC 65 (rich exhaust) and go into "open loop" operation. Under the conditions of

power enrichment, (Wide Open Throttle, WOT), the PCM sets the STFT to 0% and freezes it there until power

enrichment is no longer in effect. This is done so that LTFT will not try to correct for the commanded richness of

power enrichment.

The PCM will keep the latest LTFT values stored in its LTFT memory cells. MAF sensor readings and engine RPM

are used by the LTFT to determine what cell to read. LTFT values are stored in the PCM's long term memory, for

use each time the engine's RPM and load matches one of the LTFT cells. All LTFT values are reset to 0% when the

PCM's "long term memory power supply" is disconnected, as when diagnostic trouble codes are cleared. The Tech

2 "scan" tool also has the ability to reset LTFT to 0% with a special command.

Figure 6C2-1-71 Long Term Fuel Trim Values

LONG TERM FUEL TRIM CELL

The Long Term Fuel Trim function of the PCM is divided up into cells. These cells are arranged by the Mass Air

Flow and the Engine Speed. Each cell corresponds to a region on a MAF vs RPM table. Each region is calibrated to

a LTFT value of 0%. A value of 0% in a given block indicates no fuel adjustment is needed for that engine condition.

A higher number, say + 4%, indicates that the PCM has detected a lean exhaust, and is adding fuel to compensate.

Conversely, a lower number, say -6%, indicates that the PCM has detected a rich exhaust, and is subtracting fuel to

compensate.

As the vehicle is accelerated or decelerated the engine's LTFT calibration will change cells. As the LTFT changes

cells so does the STFT. The STFT will only make short term corrections in whatever the LTFT cell the engine is

operating in. When the engine is idling, the engine can be in one of two cells. On a vehicle with an automatic

transmission, depending upon canister purge, the engine will idle in cell 0 or 17. When the engine is running at idle

and the canister purge is ON, the LTFT would be in cell number 0 on an automatic transmission equipped vehicle.

Cells 16 and 33 are used for idle on vehicles with manual transmission.

Whatever the cell the engine is operating in, the PCM will read that cell's particular LTFT value and electronically

adjust the fuel injector base pulse width to compensate for a rich or lean condition. If an engine has a restricted fuel

filter and the customer has driven the vehicle like this for quite some time, the STFT value would be high, and the

PCM would be compensating for this condition by adding more fuel. Because the STFT value is above 0%, the

LTFT will also be greater than 0% in most of the cells to compensate for the lean exhaust. If you suspect a

driveability problem associated with an over rich or an over lean condition, then use the STFT value to detect what

the fuel control system is doing at the time. Use the LTFT to identify what the system has "learned" over a period of

time to compensate for the condition.

Use the LTFT cells to determine if the fuel control system is commanding rich or lean throughout the operating

range. If it is only rich or lean at idle or part throttle, look for components that would cause problems in these areas.

All LTFT cell values are reset to 0% when the long term memory power to the PCM is disconnected, such as when

clearing DTC's.

The Tech 2 scan tool has the ability to reset all the LTFT cells to 0% with a special command.

Figure 6C2-1-72 Long Term Fuel Trim Cell Matrix

FUEL SYSTEM OPERATION

The fuel control system starts with the fuel in the fuel tank. A single in-tank high pressure fuel pump is used. From

the high pressure pump, fuel flows through the fuel pressure supply line to a fuel filter, then onto the engine fuel rail.

The high pressure in-tank single pump is capable of providing fuel pressure greater than 575 kPa. A fuel pressure

regulator mounts between the fuel rail and the return fuel line. This keeps fuel available to the injectors at a

regulated pressure between 270 and 350 kPa.

The regulated pressure will vary, depending on the intake manifold pressure. The pressure regulator senses the

manifold pressure through a small hose connected to the throttle body housing. When the throttle body housing

pressure is low (closed-throttle), the regulated pressure is also low. When the throttle is wide open, the intake

manifold pressure and the fuel pressure are high.

Fuel in excess of the fuel injector is returned to the fuel tank by the separate return line connected to the outlet of

the pressure regulator.

The fuel injectors are located in each runner of the intake manifold. The fuel injectors are controlled by the PCM.

They deliver fuel in one of several modes, as described previously.

The fuel pump is normally energised by the PCM via the fuel pump relay.

SYSTEM COMPONENTS

The Fuel Control System is made up of the following

components.

• PCM

• Fuel pressure supply line

• Fuel pump relay

• Fuel rail

• Fuel strainer

• Fuel Injectors

• Fuel pump

• Fuel pressure regulator

•Fuel filter

• Swirl pot

• Fuel pressure regulator

• Fuel filter

• Fuel return line

• Swirl pot

Figure 6C2-1-73 Fuel Delivery System

MODULAR FUEL SENDER ASSEMBLY

The modular fuel sender assembly is attached to

the top of the f uel tank , and ex tends f r om the top of

the fuel tank to the bottom.

The modular fuel sender assembly consists of the

following major components:

• A Fuel Sender Cover

• Fuel Pipes (above cover)

• A Fuel Pump

• A Fuel Pump Strainer

• A Fuel Pump Reservoir

• A Fuel Sender Strainer

• A Ceramic Fuel Level Sensor Assembly

The fuel level sender assembly consists of the

following:

• A Float

• A Wire Float Arm

• A Rheostat

The fuel level is sensed by the position of the float

and float arm, position changes, the amount of

current passing through the rheostat varies, thus

changing the fuel gauge reading on the instrument

panel.

The V8 application uses a GEN III TURBINE fuel

pump, and can be serviced separately from the

sender unit assembly.

Figure 6C2-1-74 Modular Sender Assembly

Figure 6C2-1-75 Fuel Pump/Sender Assembly

Figure 6C2-1-76 Fuel Pump

THROTTLE BODY UNIT

The throttle body unit is single casting assembly.

The throttle body has two electrical components

connected to it. The two components are

• T he Idle Air Control (IAC) valve to contr ol the air

flow bypassing the throttle blade. This "bypass"

airflow provides the air requirements for the

engine when the throttle is closed. More

"bypass" air gives the engine the ability of a

higher idle speed. A lower flow rate of this

"bypass" air gives lower idle speeds.

• The Throttle Position (TP) Sensor , which gives

the PCM information about throttle positioning,

and if the throttle is m oving (opening or c losing).

The PCM can also determine how quickly the

throttle is opening or closing with this signal.

The throttle body contains 2 small vacuum

ports. These ports provide vacuum signals to

the evaporative emission's canister. In a V8

engine there are also 2 larger ports that are

provided for the crankcase ventilation system. Figure 6C2-1-77 Throttle Body

FUEL INJECTORS

The fuel injectors are electrically-operated fuel

control valves. The injectors are supplied B+ from

the ignition switch through the EFI relay. The fuel

injectors are controlled by the PCM which provides

the earth circuit. The PCM energises the injectors

to open. The injectors are never fully energised

"ON," as that would flood the engine with too much

fuel. The PCM supplies the earth circuit in short

pulses. The longer the duration of the pulse width

the more fuel that is injected into the engine. Inside,

the injectors have a coil that becomes an

electromagnet when energised. The resistance of

these windings is im portant for the PCM to operate

correctly.

A fuel injector which does not operate will cause a

misfire condition. An injector which is stuck partly

open could cause dieseling because fuel would be

delivered to the engine after the ignition key is

turned OFF. Figure 6C2-1-78 Fuel Injector

Figure 6C2-1-79 Fuel Injector Circuit

FUEL PRESSURE REGULATOR

The fuel pressure regulator is a diaphragm-

operated relief valve with fuel pump pressure on

one side, and intake manifold pressure (engine

vacuum) combined with mechanical spring

pressure on the other side. The function of the

regulator is to m aintain a regulated pressure at the

injector s at all tim es, by c ontrolling the flow into the

return line.

Figure 6C2-1-80 Typical Fuel Pressure Regulator

Figure 6C2-1-81 Fuel Pressure Regulator Location

FUEL PUMP ELECTRICA L CIRCUITS

When the ignition switch is turned to ON after

having been "OFF" for at least 10 seconds, the

PCM will immediately energise the fuel pump relay

to operate the fuel pump. This builds up the fuel

pressur e quickly. If the engine is not crank ed within

two seconds, the PCM will shut the fuel pum p relay

"OFF" and wait until the engine is c ranked. As s oon

as the engine begins cranking, the PCM will sense

the engine turning from the crankshaft reference

input, and turn the relay "ON" again to run the fuel

pump.

The fuel pump relay is located in the engine

compartment relay housing.

Figure 6C2-1-82 Fuel Pump Relay Location

Figure 6C2-1-83 Fuel Pump Electrical Circuits

1.6 IDLE AIR CONTROL (IAC) VALVE

The Idle Air Control (IAC) valve, contr ols the engine

idle speed. This prevents the engine from stalling

due to the changes in the engine load at idle.

The IAC valve, mounted on the throttle body,

controls the incoming air around the throttle valve

at idle. By extending the pintle (to decrease air

flow) or retr acting the pintle (to increase air flow), a

controlled amount of air can move around the

throttle valve. If the engine RPMs are too low, m ore

air is allowed to bypass around the throttle valve.

This will increase the engine speed at idle. If the

engine speed is too high, less air is bypassed

around the throttle valve. T his will dec r eas e engine

speed at idle.

The IAC valve moves in small steps from 0

(extended pintle, bypass air passage fully shut) to

196 (retracted pintle, maximum bypass airflow) as

commanded by the PCM.

At idle, the desired position of the IAC valve is

calculated by the PCM based on the following

conditions.

• The engine coolant temperature sensor

• The engine speed

• The engine load

• The battery voltage

Figure 6C2-1-84 IAC Valve Location

If the IAC valve loses voltage with the engine

running, the PCM can lose track of the actual

position of the IAC. If this happens, the PCM will

reset the IAC valve. W hen the PCM r esets the IAC

valve, the actual reset procedure occurs when the

engine speed goes above 2000 RPM after the

ignition has been "OFF" for at least 10 seconds.

The reset procedure is as follows.

The PCM commands the IAC valve to close the idle

air passageway in the throttle body. The PCM does

this by commanding "extend" pulses to move the

IAC pintle fully shut in the bore. Then, the PCM

resets the IAC valve to 0 when at a fully shut

position. Next, the PCM issues retract steps to

properly position the pintle.

Figure 6C2-1-85 IAC Valve

Figure 6C2-1-86 PCM IAC Valve Circuit

1.7 IGNITION SYSTEM

PURPOSE

The ignition system controls the fuel combustion by providing a spark to ignite the air/fuel mixture in the cy linder at

the correct time. This provides good engine performance, fuel economy, and control exhaust emissions. The PCM

controls the spark advance and the ignition dwell when the ignition system is operating in the EST mode.

The main components that make up the ignition system for the V8 SFI engine are:

• The Distributor Assembly

• The Ignition Coil

• The Ignition Module

• The PCM

• The Spark Plugs

• The Spark Plug Wires

• The Cam sensor

Figure 6C2-1-87 V8 Ignition System

DISTRIBUTOR

The distributor performs the normal distributor function of directing secondary ignition voltage from the ignition coil

to the correct cylinder by means of a rotor, distributor cap, and spark plug leads. There are no advance

mechanisms in the distributor.

IGNITION COIL

The Ignition coil's purpose is to transform the battery voltage which is low voltage high amperage to high voltage

low amperage. This high voltage output allows the spark to jump the gap of the spark plug. The ignition coil is

specifically designed for the PCM and ignition system and must not be replaced with any other type of ignition coil.

IGNITION MODULE

The ignition module, mounted separately in the

engine compartment, provides an interface

amongs t the Hall switch in the dist ributor, the PCM,

and the ignition coil. T he ignition m odule proc ess es

the Hall switch reference pulses, then sends the

signal to the PCM as a "crankshaft reference input

signal." The PCM calculates the needed spark

advance and dwell time, and sends EST output

pulses back to the ignition module. The module

triggers the ignition coil based on these EST pulses

sent from the PCM.

If the PCM detects a problem in the EST circuit or

cannot control the ignition system, the module is

capable of operating the ignition system, with a

fixed 10 degrees BTDC spark advance.

Figure 6C2-1-88 Ignition Module Location

PCM

When the ignition system is operating in the EST

mode, the PCM controls the spark timing and

dwell. The PCM, via the bypass control circuit,

commands the ignition module which of the two

modes to operate in; either the "EST m ode", or the

"bypass mode". If the module does not receive a

command from the bypass control circuit, the

ignition system will remain in the "bypass mode."

CRANKSHAFT POSITION SENSOR

The crankshaft sensor, is mounted underneath the

distributor cap.

The crankshaft sensor is a Hall-effect switch. A Hall

switch reacts like a solid-state switch, earthing a

low-current signal voltage when a magnetic field is

present. When the magnetic field is shielded from

the switch by a piece of steel placed in the air gap

between the magnet and the switch, the signal

voltage is not earthed. If the piece of steel is

repeatedly moved in and out of the air gap, the

signal voltage will appear to go "ON-OFF-ON-OFF-

ON-OFF". This ON-OFF signal occurs 4 times per

crankshaft revolution and is referred to as a 4X

reference signal. This ON-OFF signal is similar to

the signal that a set of breaker points would

generate. As a distributor shaft is turned the points

would open and close.

The c rankshaf t position sens or is used by the PCM

to determine engine speed and crankshaft

positioning. Figure 6C2-1-89 Crankshaft and Camshaft Location

1.8 ELECTRONIC SPARK TIMING (EST)

The V8 Ignition System uses the same four ignition module -to- PCM circuits as do all other Delco engine

management systems. They are as follows.

• The Crankshaft Reference PCM Input

• The Crankshaft Reference Earth

• The Bypass Control Mode

• The EST Output Mode

The Electronic Spark Timing is the PCM's method of controlling spark advance and ignitions dwell, when the ignition

system is operating in the EST mode.

There are two modes of ignition system operation:

• Bypass mode

• EST mode

In the bypass mode, the ignition system operates` independently of the PCM, with the bypass mode spark advance

always at 10 degrees BTDC. The bypass mode is in affect when cranking the engine. The PCM has no control of

the ignition system when in this mode.

After the engine starts (RPM greater then 450 RPM, the PCM will command the ignition system to go into the EST

mode. The ignition spark advance will remain in the EST mode until one of the following conditions occurs.

• The ignition key is turned OFF.

• The engine quits running.

• An EST fault is detected.

If an EST fault is detected while the engine is running, the ignition system will switch back to the bypass mode. The

engine may quit running, but will restart and stay in the bypass mode.

In the EST mode, the ignition spark timing and ignition dwell time is fully controlled by the PCM. The EST spark

advance and the ignition dwell is calculated by the PCM using the following inputs.

• Engine speed Crankshaft reference

• Crankshaft position Crankshaft reference

• Engine load MAF

• Engine coolant ECT temperature

• Throttle position TP sensor

• Park/Neutral TFP

• Detonation Knock sensor

• Vehicle speed VSS

• Diagnostic request DLC diagnostic "test" input terminal

• PCM supply voltage

The following describes the four PCM-to-ignition module circuits.

Figure 6C2-1-90 Ignition System with EST Circuits Show n

CRANKSHAFT REFERENCE PCM INPUT

From the ignition module, the PCM uses this signal to calculate the engine RPM and the crankshaft position. The

PCM compares pulses on this circuit to any pulses that are on the earth circuit. The PCM also uses the pulses on

this circuit to initiate injector pulses. If the PCM doesn’t receive any pulses on this circuit, no fuel injection pulses will

occur, the engine will not run, and a DTC 46 will set when attempting to start the engine.

CRANKSHAFT REFERENCE EARTH

This is an earth circuit for the digital RPM counter inside the PCM. The wire is connected to engine earth through

the ignition module. Although this circuit is electrically connected to the PCM, it is not connected to earth at or

through the PCM. If the circuit is open, or earthed at the PCM, it may cause poor engine performance and possibly

a "Check Powertrain" lamp with no DTC set.

BYPASS CONTROL

The PCM either allows the ignition module to keep the spark advance at the "bypass mode" 10 degrees BTDC, or

the PCM signals the ignition module that the PCM is going to control the spark advance (EST mode). The ignition

module switches between the modes by the level of voltage that the PCM sends to the ignition module on the

bypass control circuit. The PCM provides 5 volts to the ignition module if the PCM is going to control spark timing

(EST mode). If the PCM does not turn supply the 5 volts, or if the ignition module doesn't receive it, then the module

will keep control of spark timing (bypass mode). An open or short to the voltage bypass control circuit will set a DTC

42. While a DTC 42 is set the ignition system will stay in the "bypass mode." If the bypass control circuit becomes

earthed during the EST mode and engine speed is greater than 1600 RPM, the engine may stall, but will restart. A

DTC 42 will set, and the ignition system will operate in the bypass mode.

EST OUTPUT

In the EST mode the PCM sends timing pulses to the ignition module. These pulses are the ignition timing pulses

used by the ignition module to energise the ignition coil. If the EST output circuit is open or shorted to voltage when

the engine is started, a DTC 41 will set and the ignition system will stay in the bypass mode. If the EST Output

circuit becomes earthed during the EST mode above an engine speed of 1600 RPM, the engine may stall, but will

restart. A DTC 42 will set, and the ignition system will operate in the bypass mode.

RESULTS OF INCORRECT OPERATION

An open or an earth in the EST or bypass circuit will set a DTC 41 or a DTC 42. If a fault occurs in the EST output

circuit when the engine is running, the engine may stumble or stall but will restart and run in the bypass mode. A

fault in either circuit will force the ignition system to operate on bypass mode timing (10 degrees BTDC), which will

result in reduced performance and fuel economy.

1.9 KNOCK SENSOR (KS) SYSTEM

PURPOSE

Varying octane levels in today's petrol may cause

detonation in some engines. Detonation is caused

by an uncontrolled pressure in the combustion

cham ber . This uncontrolled pr es sur e c ould produc e

a flam e f r ont oppos ite that of the normal flam e f r ont

produced by the spark plug.

The "rattling" sound normally associated with

detonation is the result of two or more opposing

pressures (flame fronts) colliding within the

combustion chamber. Though "light" detonation is

sometimes considered normal, "heavy" detonation

could result in engine damage. Light detonation

occurs when the point of maximum pressure has

been exceeded.

To control spark knock, a Knock Sensor (KS)

System is used. This system is designed to retard

the spark timing up to 12 degrees. This allows the

engine to use maxim um spark advance to im prove

the driveability and the fuel economy. Figure 6C2-1-91 Knock Sensor

OPERATION

The Knock Sensor (KS) system has two major

components:

• The KS Module (part of PROM)

• The Knock Sensor

The knock sensor detects abnormal mechanical

vibration (spark knocking) in the engine. There are

several calibrations of knock sensors because

each engine produces a different frequency of

mechanical noise. The knock sensor is specifically

chosen f or this engine to best detect engine knock .

This engine has one knock sensor. The knock

sensor is mounted on the engine block near the

cylinders to better detect engine detonation.

Figure 6C2-1-92 Knock Sensor Location

Figure 6C2-1-93 PCM Knock Sensor Wiring

A knock sensor is used to detect engine

detonation. The PCM will retard the Electronic

Spark Timing (EST) based upon the signals being

received.

The PCM supplies a 5 volt signal to the knock

sensor. The shunt resistor inside the knock sensor

keeps the voltage at approxim ately 2.5 volts. Under

a no knock condition, the circuit should be about

2.5 volts. The knock sensor produces an AC

voltage that rides on top of the 2.5 volts DC voltage

and increases in amplitude and in signal frequency

with the severity of the k noc k . This signal voltage is

used as an input to the PCM. This AC signal

voltage to the PCM is proces sed by a Signal Noise

Enhancement Filter (SNEF) module. The SNEF

module is used to determine if the AC signal

coming in is noise or detonation. This SNEF

module is part of the PROM and cannot be

replaced. The PCM then adjusts the ignition timing

to reduce the spar k advance. How m uch the tim ing

is retarded is bas ed upon the amount of time knock

that is detected and is limited to a maximum value

of 12 degrees. After the detonation stops, the

tim ing will gradually return to it's calibr ated value of

spark advance. The Knock Sensor s ys tem will only

retard timing after the following conditions are met:

• The engine run time is greater than 5 seconds.

• The engine speed is greater than 1000 RPM.

• The engine coolant temperature is greater than

44°C.

Figure 6C2-1-94 Knock Sensor Sectioned View

The Tech 2 Scan tool has two data display

parameters to check for diagnosing the knock

sensor circuit. The "KNOCK SIGNAL" is used to

monitor the input signal from the knock sensor.

This will display "YES" when knock is being

detected. "KNOCK RETARD" is the indication of

how much the PCM is retarding the spark advance.

A DTC 43 is designed to diagnose the knock

sensor and the wiring. A DTC 43 will diagnose an

open or a short in the wiring circuit. When a DTC

43 is set, the PCM will retard the total spark

advance by 6 degrees.

1.10 EVAPORATIVE EMISSION CONTROL

The Evaporative Emission Control System (EECS)

used on this vehicle is the charcoal canister

storage m ethod. This method transfers f uel vapour

from the fuel tank to an activated car bon (charcoal)

storage device (canister) located under the rear of

the vehicle, to hold the vapours when the vehicle is

not operating. W hen the engine is running, the fuel

vapour is purged from the carbon element by intake

air flow and consumed in the normal combustion

process.

Figure 6C2-1-95 Fuel Vapour Canister

This system has a remote mounted canister purge

control solenoid. The PCM operates this solenoid

to control vacuum to the canister. Under cold

engine conditions, the solenoid is turned "OFF" by

the PCM, which blocks vacuum to the canister to

prevent purge.

The PCM turns ON the solenoid valve and allows

purge when the following conditions have been

met.

• The engine coolant temperature is less than 80

degrees C, 3 minutes and 10 seconds after

engine start.

• The engine coolant temperature is greater than

80 C, 15 seconds after engine start.

• The engine coolant temperature is above 60

degrees C.

• The engine is not in Decel Fuel Cutoff Mode.

• The throttle opening is less than 92%.

• The engine is in Closed Loop Fuel Mode or

Open Loop Fuel Mode.

The canister cannot be repaired, and is serviced

only as an assembly. Periodically check the

canister at the time or distance intervals specified

in the Owner's Handbook.

Figure 6C2-1-96 Canister Purge Solenoid Location

Figure 6C2-1-97 Canister Purge Solenoid Circuit

The fuel vapour canister is mounted in a bracket

under the body, near the fuel filter.

Figure 6C2-1-98 Canister Location

The c anister is a three port des ign. The f uel vapour

is absorbed by the charcoal within the canister.

When the engine is running at idle speed and

above idle, air is drawn into the canister through the

atmospheric port at the top of the canister

assembly. The air mixes with the fuel vapour and

the mix tur e is dr awn into the intak e manif old via the

canister purge line. The Uppermost port on the

canister is controlled by the PCM controlled

canister purge solenoid. The canister purge

solenoid controls the manifold vacuum signal from

the throttle body. The port below the canister purge

port is the vapour inlet from the fuel tank. The

single off centre port is open to the atmosphere.

Figure 6C2-1-99 Sectioned View of Canister

RESULTS OF INCORRECT OPERATION

• Poor idle, stalling and poor driveability can be

caused by one of the following conditions.

-An inoperative canister purge solenoid.

-A damaged canister.

-Hoses split, cracked and/or not connected

to the proper tubes.

• An evidence of fuel loss or fuel vapour odour

can be caused by one of the following

conditions.

-A Liquid fuel leaking from fuel lines.

-A Cracked or damaged canister.

-is connected, misrouted, kinked,

deteriorated or damaged vapour hoses, or

control hoses.

If the solenoid is s tuc k open, or the c ontrol c irc uit is

shorted to earth the c anis ter will purge to the intake

manifold all the time. This can allow extra fuel at

idle or during warm-up, which can cause rough or

unstable idle or a rich fuel operation.

If the canister purge solenoid is always closed, the

canister can become overloaded, with f uel res ulting

in fuel odour.

A fault in the canister purge s olenoid or circuit m ay

result in DTC 97.

Figure 6C2-1-100 EVAP System Typical

1.11 ELECTRIC COOLING FAN

Figure 6C2-1-101 Cooling Fan Circuit

The V8 engine has two, two speed electric engine

cooling fan assembly that provides the primary

means of moving air through the engine radiator.

The two, two speed electric cooling f an are us ed to

cool engine coolant flowing through the radiator.

The two, two speed electric cooling fans are also

used to cool the ref rigerant f lowing through the A/C

condenser (if fitted). Each engine cooling fan m otor

has four terminals, two negative and two positive

terminals. The two negative terminals are the relay

controlled circuits for the fan operation. The two

positive terminals are the direct power feed from a

fusible link to the fan motors. When an earth signal

is applied to one of the negative term inals, the fan

motor will operate at low speed. When a earth

signal is applied to both negative terminals, both

fan will operate at high speed.

The engine cooling fan high speed relay is

controlled by the PCM. The PCM controls the earth

path for the engine cooling fan high speed relay.

The low speed of the electric fan is controlled by

the PCM through a special Data Com munic ation to

the BCM. The BCM controls the earth path for the

engine cooling fan low speed relay. The engine

cooling fan high speed relay and the engine

cooling fan low speed r elay are used to c ontrol the

earth signal to the electr ic m otor that drives the five

bladed fan.

The PCM determines operation of the two, two

speed engine cooling fan based on A/C request,

engine coolant temperature, A/C Refrigerant

Pressure Sensor, and vehicle speed signal inputs.

There are four (4) suppression capacitors

incorporated into the fan motor wiring circuits.

These suppression capacitors help eliminate fan

motor noise through the radio speakers. If these

capacitors are open, then noise will be present

through the radio speak ers. If shorted to earth, the

fan motors could continuously run, or the fuse or

fusible link could fail.

Figure 6C2-1-102 Engine Cooling Fan Assembly

ENGINE COOLING FAN LOW SPEED

The engine cooling fan low speed relay is

energised by the BCM. The PCM determ ines when

to enable the low speed fan based on inputs from

the BCM serial data, Engine Coolant Temperature

(ECT) sensor and the Vehicle Speed Sensor

(VSS). The cooling fan low speed relay will be

turned "ON'' when:

• The A/C request indicated (YES) and either

the vehicle speed is less than 30 km/h.

- OR -

• A/C pressure is greater than 1500 kPa

- OR -

• The coolant temperature is greater than 95

degrees C.

If the coolant temperature is greater than 117

degrees C when the ignition is switched off, the

relay is energised for up to approximately 4

minutes.

If an engine coolant temperature sensor fault is

detected, such as DTC 14, 15, 16 or 17.

The cooling fan low speed relay will be turned

"OFF'' when any of the following conditions have

been met :

• The A/C request is not indicated (NO)

• The A/C request is indicated (YES) and the

vehicle speed is greater than 50 km/h and A/C

pressure is less than 1170 kPa.

Figure 6C2-1-103 Cooling Fan Relay Locations

ENGINE COOLING FAN HIGH SPEED

The engine cooling fan high speed relay is

controlled by the PCM based on input from the

Engine Coolant Temperature (ECT) sensor. The

PCM will only turn "ON'' the engine cooling fan high

speed relay fan if the engine cooling fan low s peed

relay has been "ON" for 2 seconds and the

following conditions are satisfied.

• There is a BCM message response fault which

will cause a DTC 92

• An engine coolant temperature sensor fault is

detected such as DTC 14,15,16,17.

• Coolant temperature greater than

104 degrees C.

The engine cooling fan high speed relay can also

be enabled by the A/C Refrigerant Pressure

Sensor. When the A/C Refrigerant Pressure

Sensor determines the A/C system pressure is to

high, greater than 2600 kPa, and this will instruct

the PCM to enable the high speed fan.

If the low speed fan was "OFF" when the criteria

was met to turn the high speed fan "ON", the high

speed fan will come "ON" 5 seconds after the low

speed fan is turned "ON". " If both the engine

cooling fan relays are "ON", the PCM will turn

"OFF" the high speed relay when:

The engine coolant temperature is less than 99

degrees C.

• A/C request not indicated (NO)

• A/C request indicated (YES) and A/C pressure

is less than 2300 kPa.

1.12 A/C CLUTCH CONTROL

This vehicle uses one of two types of A/C clutch controls. Either a standard A/C type or an Electronic Climate

Control (ECC) module type.

A/C CLUTCH CONTROL WITH ELECTRIC CLIMATE CONTROL

Figure 6C2-1-104 A/C Clutch Control With ECC

With the ECC system, when the A/C is requested,

the Electronic Climate Control Module will supply a

signal to the BCM. The BCM will then send a serial

data request to the PCM. W hen the PCM receives

the serial data request on PCM terminal B12, the

PCM will indicate that air conditioning has been

requested. Approximately 1/2 second after the

PCM receives this s ignal, the PCM will energise the

A/C control relay. This serial data signal to the PCM

is also used to adjust the idle speed before turning

"ON" the A/C compressor relay. If this signal is not

available to the PCM, the A/C compressor will be

inoperative.

If there is a problem with the PCM A/C Relay

Control circuit, QDSM DTC 91 will set.

The BCM also supplies the earth signal from BCM

terminal "7" to the low speed cooling fan relay.

This A/C system also incorporates a A/C

Refrigerant Pressure Sensor. The A/C Refrigerant

Pressure Sensor signal indicates high side

refrigerant pressure to the PCM. The PCM uses

this infor mation to adj ust the idle air c ontrol valve to

compensate for the higher engine loads present

with high A/C refrigerant pressures. A fault in the

A/C Refrigerant Pressure Sensor signal will cause

DTC 96 to set.

Figure 6C2-1-105 A/C Refrigerant Pressure Sensor

Location

The PCM will NOT energise the A/C control

relay if any of the following conditions are

present.

• The engine speed is gr eater than 5,800 RPM. If

disabled because of RPM, the A/C can be

enabled when the RPM falls below 5,400 RPM.

• The throttle is greater than 99%. When dis abled

during wide-open throttle, the A/C will enable

when the throttle is less than 93%.

On vehicles equipped with non-ECC systems the

power flow is diff erent. W ith the blower fan and the

air conditioning switched "ON," switched ignition

voltage is supplied from fuse F13 through the A/C

master switch, and then to the BCM. The BCM will

then supply a serial data signal to the PCM

requesting A/C. If the BCM does not receive a

earth signal from the blower switch to BCM terminal

"3", the BCM will not supply the serial data request

for A/C. Once the PCM receives this serial data

signal, the PCM will energise the A/C compressor

relay. The BCM also supplies the earth signal from

BCM terminal "7" to the low speed cooling fan

relay.

This serial data signal to the PCM is also used to

adjust the idle speed before turning "ON" the A/C

compressor relay. If this signal is not available to

the PCM, the A/C compressor will be inoperative.

This system, lik e the ECC system als o inco rpor ates

a A/C Refrigerant Pressure Sensor. The A/C

Refrigerant Pressure Sensor signal indicates high

side refrigerant pressure to the PCM. The PCM

uses this information to adjust the idle air control

valve to compensate for the higher engine loads

with high A/C refrigerant pressures. A fault in the

A/C Refrigerant Pressure Sensor signal will cause

a DTC 96 to set.

Figure 6C2-1-106 A/C Relay Location

A/C CLUTCH CONTROL WITH NON ECC AIR CONDITIONING

With the blower fan ON, and the air conditioning ON, the switched ignition voltage is supplied from fuse F13

through the A/C master switch, and then to the BCM. The BCM will then supply a serial data signal to the PCM

requesting A/C. If the BCM does not receive a earth signal from the blower switch to BCM terminal "3", the BCM will

not supply the serial data request for the A/C. Once the PCM receives the serial data signal, the PCM will energise

the A/C compressor relay by supplying a earth signal (A/C Relay Control ). The BCM also supplies a earth signal

from BCM terminal "7" to the low speed cooling fan relay.

This serial data signal to the PCM is also used to adjust the idle speed before turning ON the A/C compressor relay.

If this signal is not available to the PCM, the A/C compressor will be inoperative.

This system also incorporates an A/C Pressure Transducer. The A/C Pressure Transducer signal indicates low side

and high side refrigerant pressure to the PCM. The PCM uses this information to adjust the idle air control valve to

compensate for the higher engine loads present with high A/C refrigerant pressures.

The purpose of the A/C Pressure Transducer is to protect the system from damage due to either the refrigerant

pressure being too low (which could damage the compressor due to insufficient lubrication), or too high (which

could result in a leak in the sealed refrigerant R134a system).

The PCM will NOT energise the A/C control relay if any of the following conditions are present:

• The engine speed is greater than 4,800 RPM. If de-energised because of RPM, it can re-energised when the

speed falls below 4,000 RPM for at least 10 seconds.

• The Throttle Position sensor is greater than 90% open.

Figure 6C2-1-107 PCM A/C Clutch Control Without ECC

1.13 ABBREVIATIONS AND GLOSSARY OF TERMS

Abbreviations used are listed below in alphabetical order with an explanation of the abbreviation.

AC - ALTERNATING CURRENT - A current whose polarity is constantly changing between positive and negative.

A/C - AIR CONDITIONING

A/F - AIR/FUEL (A/F RATIO)

ANALOG SIGNAL - An electrical signal that varies in voltage within a given parameter.

BAROMETRIC PRESSURE - Atmospheric pressure. May be called BARO, or barometric absolute pressure.

BATTERY - Stores chemical energy and converts the chemical energy into electrical energy. This provides DC

current for the vehicles electrical systems.

CAT. CONV - CATALYTIC CONVERTER - A muffler-shaped device fitted in the exhaust system, between the

engine and the muffler. The purpose of the catalytic converter is to chemically convert engine producing gases into

environmentally safe gases. HC, CO, and NOx emitted by the engine, are converted to water vapour, carbon

dioxide, and nitrogen.

"CHECK POWERTRAIN" LAMP - A Warning indicator located on the instrument panel, and controlled by the PCM.

The lamp is illuminated by the PCM when it detects a fault in the engine management system, or when the ignition

is "ON" with the engine not running (bulb check).

CKT - CIRCUIT

CLOSED LOOP - A fuel control mode of operation that uses the signal from the exhaust oxygen sensor, in order to

control the air/fuel ratio precisely at a 14.7 to 1 ratio. This allows maximum efficiency of the catalytic converter.

CO - CARBON MONOXIDE - One of the pollutants found in the engine exhaust.

DIAGNOSTIC TROUBLE CODE - The PCM can detect faults in the engine management system. If a fault occurs,

the PCM may turn on the "Check Powertrain" lamp and a two digit code number will set. A diagnostic trouble code

can be read from the PCM through the "Check Powertrain" lamp or with the Tech 2 scan tool. This DTC will indicate

the area of the fault.

DIAGNOSTIC "TEST" ENABLE TERMINAL - A terminal in the Data Link Connector(DLC) that is earthed to get a

Diagnostic Trouble Code.

DIGITAL SIGNAL - An electrical signal that is either ON or OFF.

DLC - DATA LINK CONNECTOR - Used at the assembly plant to evaluate the engine management system. For

service: to flash the "Check Powertrain" lamp, use of Tech 2 scan tool, & making other system checks.

DLC DATA STREAM - An output from the PCM, initiated by the Tech 2 scan tool. This output is a digital signal,

used by assembly plant test equipment and the Tech 2 scan tool. This signal is transmitted from the PCM to the

Data Link Connector(DLC).

DRIVER - An electronic device, usually a power transistor, that operates like an electrical switch turning a circuit

“ON” and “OFF”.

DUTY CYCLE - The time, in percentage, that a circuit is "ON" versus "OFF" .

DVM (10 Meg.) - DIGITAL VOLTMETER - A multipurpose meter that has capability of measuring Voltage, Amps,

and Resistance.

FIELD SERVICE MODE - A PCM mode of operation that is used during service. It is operational when the engine is

running and the DLC diagnostic "test" enable terminal is earthed.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR - A sensor that senses the engine coolant temperature and

sends that information to the powertrain control module.

EECS - EVAPORATIVE EMISSIONS CONTROL SYSTEM - Used to prevent petrol vapours from the fuel tank from

entering into the atmosphere. The vapours are stored in a canister, located in the engine compartment. The

canister contains an activated charcoal element. The petrol vapours are purged from the canister into the manifold

to be burned in the engine.

EMI OR ELECTRICAL NOISE - An unwanted signal interfering with another needed signal. Common examples are

an electric razor's effect on a television, or AM radio reception while driving under high voltage power lines.

EPROM - ERASABLE PROGRAMMABLE READ ONLY MEMORY - Type of read only memory (ROM) that can be

erased with ultraviolet light and reprogrammed.

ESD - ELECTROSTATIC DISCHARGE - The discharge of static electricity, which has built up on an insulated

material.

EEPROM - ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY - Ty pe of read only memory

(ROM) that can be electrically programmed, erased and reprogrammed.

FIELD SERVICE MODE - A PCM mode of operation that is used during service. The field service mode is

operational when the engine is running and the DLC diagnostic "test" enable terminal is earthed.

FUSE - A thin metal strip which melts through when excessive current flows through it, creating an open circuit.

Protecting a circuit from damage.

HC - HYDROCARBONS (HC) - Any unburned fuel leaving the engine from incomplete combustion.

IAC VALVE- IDLE AIR CONTROL VALVE - Installed on the throttle body unit and controlled by the PCM to regulate

idle air flow, and thus idle RPM.

IAT SENSOR- INTAKE AIR TEMPERATURE SENSOR - A sensor that senses intake manifold incoming air

temperature, and sends the information to the PCM.

IDEAL MIXTURE - The air/fuel ratio which provides the best performance, while maintaining maximum conversion

of exhaust emissions, typically 14.7 to 1 on petrol engines.

IGN - IGNITION

INPUTS - Information from sensors (MAF, TPS, etc) and switches (A/C request, etc.) used by the PCM to

determine how to control its outputs.

INTERMITTENT - An electrical signal that occurs now and then; not continuously. In electrical circuits, refers to

occasional open, short, or earth in a circuit.

IPC - INSTRUMENT PANEL CLUSTER

LOW - A voltage less than a specific threshold. Operates the same as an earth and may, or may not, be connected

to chassis earth.

MAF - MASS AIR FLOW SENSOR - A device that monitors the amount of air flow coming in the engine intake. The

MAF sensor sends a signal to the PCM.

N.C. - NORMALLY CLOSED - Switch contacts that are closed, when they are in the normal operating position.

N.O. - NORMALLY OPEN - Switch contacts that are normally open when in the normal operating position.

NOx - NITROGEN OXIDE - One of the pollutants found in gasoline engine exhaust. The are formed from normal

combustion and increase in severity with combustion temperatures.

OXYGEN SENSOR - The exhaust gas oxygen sensor is located in the exhaust manifold. The O2 sensor measures

the oxygen in the exhaust manifold after the combustion process. The O2 sensor produces a small electrical signal

based on the amount of oxygen in the exhaust gas.

OPEN LOOP - The PCM control of the fuel control system without the use of the oxygen sensor information.

OUTPUT - Functions, typically include solenoids and relays, that are controlled by the PCM.

PCM - POWERTRAIN CONTROL MODULE. A metal cased box containing electronic circuitry w hich electrically

monitors and controls the transmission system and emission systems on the engine management system. It also

turns "ON" the "Check Powertrain" lamp when a malfunction occurs in the system.

PCV - POSITIVE CRANKCASE VENTILATION - Method of reburning crankcase fumes, rather than passing them

directly into the atmosphere.

PROM - PROGRAMMABLE READ ONLY MEMORY - An electronic term used to describe the engine calibration

unit. A plug-in memory unit that instructs the PCM how to operate for a particular vehicle.

PULSE WIDTH MODULATED (PWM) - A digital signal turned "ON" and "OFF'" for a percentage of available on-

plus-off cycle time such as, 30% "on" and 70% "off" would be called a 30% "ON" PWM signal.

QUAD DRIVER - A transistor in the PCM, capable of operating four separate outputs. Outputs can be either "ON-

OFF" or pulse width modulated.

RAM - RANDOM ACCESS MEMORY - Is the microprocessors "scratch pad". The processor can write into, or read

from this memory as needed. This memory is volatile and needs a constant supply of voltage to be retained. If the

voltage is lost or removed, this memory is lost.

SERIAL DATA - Serial date is a series of rapidly changing voltage signals pulsed from high to low voltage. These

voltage signals are typically 5 volts (high) and 0 volts (low) and are transmitted through a wire often referred to as

the serial data line.

SFI - SEQUENTIAL FUEL INJECTION - Method of injecting fuel into the engine. Places a fuel injector at each inlet

port of a cylinder head, directly in front of the intake valve, mounted in the intake manifold.

SOLENOID - An electromagnetic coil which creates a magnetic field when current flows through it and causes a

plunger or ball to move.

SWITCH - Opens and closes circuits, thereby controlling current flow.

TCC - TORQUE CONVERTER CLUTCH - A PCM controlled solenoid in an automatic transmission which positively

couples the transmission input shaft to the engine.

TECH 2 SCAN TOOL - A hand-held diagnostic tool, containing a microprocessor that reads the PCM's DLC data

stream. A display panel displays the PCM's input signals and output commands.

TP SENSOR - THROTTLE POSITION - A sensor that sends a signal to the PCM. The PCM can determine from

this signal the current throttle position, and the rate of throttle opening / closing.

VACUUM, MANIFOLD - A vacuum source from below the throttle plate.

VACUUM, PORTED - Vacuum source from a small "port" in the throttle body. With the throttle closed, there is no

vacuum, because the port is on the air cleaner side of the throttle blade, and is exposed to engine vacuum only after

the throttle is open.

VSS - VEHICLE SPEED SENSOR- A permanent magnet type sensor which produces an AC voltage which is sent

to the PCM to determine vehicle speed.

UART - UNIVERSAL ASYNCHRONOUS RECEIVE AND TRANSMIT - A method of communicating between

electronic devices.

WOT - WIDE OPEN THROTTLE - A throttle position opening greater than 80%.