SECTION 6C2-2B SYMPTOMS - 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 b elt
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.
When no diagnostic trouble codes are set and the Tech 2 scan tool data values are within the typical ranges, you
should diagnose the condition based on the symptoms of the complaint.
This Symptom Section starts with preliminary checks that must be performed in order to diagnose by the symptom.
Then, intermittent conditions are discussed. These preliminary checks provide important information to assist you
with symptom diagnosis. Next, the contents of this Section presents the various symptoms and lists a series of
checks for each symptom.
Many of the symptom diagnostics start with a visual/physical inspection. Always look for the obvious. Some
situations may warrant observing the driver. Is the driver using the correct shift lever position or riding the brake
pedal? Visually check the engine, the transmission, and the PCM connectors. Are there any disconnected wires or
incorrectly installed components? Finally, are there obvious signs that someone may have performed incorrect
repairs? These checks take very little time; they can eliminate the time spent on a broad-base systematic diagnosis
by directing you to the problem. If they do not reveal the problem, proceed to check the other suspect systems, as
shown.
The last parts of this Section contain PCM connector symptom charts. If you are diagnosing a problem, scan the
right-most column for the symptom(s) and check for the correct wire and the correct voltage at the designated
connector cavity.
PCM AND PROM
The PCM can have a fault which may affect only one circuit. Follow the Diagnostic Procedures in this section to
determine which circuit has a problem and where the problem is.
If a diagnostic chart indicates that the PCM is the cause of a problem, and the PCM is replaced, but does not
correct the problem, one of the following may be the reason:
• There is a problem with the PCM terminal connections. The diagnostic chart will say "PCM connections or PCM."
The terminals may have to be removed from the connector in order to check them properly.
• The PCM or the PROM is not correct for the application. The incorrect PCM or the incorrect PROM may cause a
malfunction and may not set a DTC.
• The problem is intermittent. In this case, refer to the "Symptoms" Charts and make a careful physical inspection
on all the components of the systems involved.
• A shorted solenoid, a shorted relay coil, or a shorted harness. Solenoids and relays are turned "ON" and "OFF"
by the PCM. The PCM uses internal electronic switches called "Drivers” to switch these solenoids and relays ON
and OFF. Each driver is part of a group of four (called "Quad drivers"). A fault in a driver may cause other drivers
in the set to malfunction. Solenoid and relay coil resistance must measure more than 20 ohms, in most cases.
Less resistance may cause an early fault of the PCM "driver."
• Before replacing a PCM, check the coil resistance of all the solenoids and all the relays controlled by the PCM.
See PCM wiring diagram for the solenoid(s) and relay(s) and the coil terminal identification.
• The PROM may be faulty. Although these rarely fail, they operate as part of the PCM. Therefore, a PROM could
be the cause of the problem. Substitute a known good PROM.
• The replacement PCM may be faulty. After the PCM is replaced, the system should be rechecked for the proper
operation. If the diagnostic chart again indicates that the PCM is the problem, substitute a known good PCM.
This is an extremely rare condition.
Figure 6C2-2B-1 Powertrain Wiring Harness to Engine Assembly Earth Locations
IMPORTANT PRELIM INARY CHECKS
BEFORE USING THIS SECTION
Before using this Symptoms Section you should have performed the "On Board Diagnostic System Check" as
detailed in Section 6C2-2A DIAGNOSIS CHARTS and have determined that:
1. The PCM and the "Check Powertrain" lamp are operating correctly.
2. There is a Diagnostic Trouble Code stored in the PCM memory and the Check Powertrain Lamp is not ON.
3. The diagnostic chart for the diagnostic trouble code indicates that the trouble is intermittent.
4. Figure 6C2-2B-1 illustrates the Powertrain wiring harness to engine assembly earth locations as described in
the various "SYMPTOM CHARTS" in this Section. Familiarise yourself with these locations.
SYMPTOM
Verify the customer complaint, and locate the correct symptom in the table of contents. Check all the items
indicated under that symptom.
If the ENGINE CRANKS BUT WILL NOT RUN, refer to Chart A-3.1 in Section 6C2-2A.
VISUAL/PHYSICAL CHECK
Perform a Careful Visual/Physical Check. This can lead to correcting a problem without further checks. This check
should include:
• A check of the service records for any repairs that may indicate a related problem, or the need for scheduled
maintenance.
• Checking the PCM sensors for being in their proper location.
• Checking the PCM earth circuits at 2 separate terminals. On a V8 engine these attach to the engine at two
locations: the rear of the left cy linder head, and at the generator support (refer Fig. 6C2-2B-1). The earth
terminals must be clean and tight. Check for earth terminals that may be loose under the retaining nuts/bolts, or
for terminals that may have been left off after an engine repair. Any repair of the wire to the terminal connection
must include soldering with rosin core solder. (NEVER use acid core solder for any wiring repairs.)
• Checking the vacuum hoses for splits, kinks, and for the proper connections. Check thoroughly for any type of
leak or restriction.
• Checking for air leaks at the throttle body mounting area and at the intake manifold sealing surfaces.
• Checking the ignition wires for cracking, carbon tracking and for the proper routing.
• Checking the wiring harness for improper connections, pinches and cuts.
• Checking the installation of any non genuine Holden's options or accessories that may have been fitted to the
vehicle that could cause the problem.
INTERMITTENTS
DEFINITION:
Problem may not turn ON the "Check Powertrain" lamp or store a DTC. Do not use the diagnostic trouble code
charts for intermittent problems. When using the DTC charts the fault must be present to locate the problem. If a
fault is intermittent, use of the DTC charts may result in the replacement of good parts.
• Most intermittent problems are caused by a faulty electrical connections or faulty wiring. Perform careful
visual/physical checks as described at the start of this Section - "IMPORTANT PRELIMINARY CHECKS".
Check for:
-The proper mating of the connector halves or terminals not fully seated in the connector body.
-Improperly formed or damaged terminals. All connector terminals in the problem circuit should be carefully
reformed or replaced to assure the proper contact tension.
-Poor terminal to wire connection. This requires removing the terminal from the connector body to check as
outlined in the service operations.
-The PCM earth circuit terminals being loose at the engine. On a V8 these attach to the engine at two
separate locations: the rear of the left cylinder head, and the generator support. Refer to Fig. 6C2-2B-1 at the
beginning of this section.
• If a visual/physical check does not find the cause of the problem, the car can be driven with a voltmeter
connected to the suspected circuit. A Tech 2 scan tool can also be used to help detect intermittent conditions.
An abnormal voltage, or an abnormal Tech 2 scan tool reading, when the problem occurs, will indicate the
problem circuit. If the wiring and connectors check OK, and a diagnostic trouble code is stored for a circuit
having a sensor, except for DTC 44, DTC 45, DTC 64 and DTC 65, substitute a known good sensor and then
recheck.
• Loss of the diagnostic code memory. To check for a loss of memory, disconnect the TP sensor and allow the
engine to idle until the "Check Powertrain" lamp comes ON. A DTC 22 should be stored, and kept in memory
when ignition is turned OFF. If not, the PCM is faulty.
• An intermittent "Check Powertrain" lamp with no stored diagnostic trouble code may be caused by:
- An ignition coil that is shorted to earth and is arcing at the spark plug wires or at the spark plugs.
- The "Check Powertrain" lamp wire to the PCM shorted to earth.
- The PCM earth circuit terminals being loose. The PCM earth terminals are attached to the engine at two
separate locations. The rear of the left cylinder head, and at the generator support. Refer to Fig. 6C2-2B-1.
- An intermittent short to B+ on the 5 volt input circuit (diagnostic request).
• An electrical system interference caused by a defective relay, a defective PCM driven solenoid, or a defective
switch. They can cause a sharp electrical surge. Normally, the problem will occur when the faulty component is
operated.
• Check for the improper installation of non-factory installed electrical options such as lights, 2 way radios, etc.
• The EST wires should be routed away from the spark plug wires, the ignition wires, the distributor assembly and
the generator. The wire from the PCM to the ignition should have a good connection.
• Check for an open diode across the A/C compressor clutch, and for other open diodes (refer to wiring diagrams
and CHART A-11.1 or CHART A-11.3 wiring diagrams in Section 6C2-2A).
• If the problem has not been found, refer to the proper symptom and perform all the checks listed.
HARD START
DEFINITION:
Engine cranks OK, but does not start for a long time. Does eventually run, or may start but immediately stalls.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as described at the start of this Section - " IMPORTANT
PRELIMINARY CHECKS".
• Make sure the driver is using the correct starting procedure. Do not depress accelerator pedal during cranking.
• CHART A-3.1 "ENGINE CRANKS BUT WILL NOT RUN" in Section 6C2-2A. Although this chart may not
exactly describe the problem, most of the causes of a "no start" can also cause a "hard start".
• Time or kilometres since normal engine tune-up has been performed. Refer to time/distance intervals in owner's
handbook.
• Check the PCM earth circuit terminals for being loose at the engine. On a V8 these attach to the engine at two
separate locations: the rear of the left cylinder head, and the generator support. Refer to Fig. 6C2-2B-1 at the
beginning of this Section.
SENSORS
CHECK:
The Engine Coolant Temperature (ECT) sensor using a Tech 2 scan tool, compare the engine coolant
temperature with the ambient temperature on cold engine.
If the engine coolant temperature reading is 5 °C greater than or 5 °C less than ambient air temperature on a
cold engine, check the resistance of the ECT sensor and the ECT sensor circuit. Compare the ECT sensor
resistance values to the Diagnostic Aids chart on the DTC 15 chart in Section 6C2-2A.
CHECK:
The MAF sensor for being shifted. Refer to CHART A-6.1 "MAF SENSOR OUTPUT CHECK" in Section 6C2-
2A.
CHECK:
The TP Sensor for binding or a high TP sensor voltage with the throttle closed.
IGNITION SYSTEM
CHECK:
The spark plug leads for being misrouted at the coil or at the spark plugs.
CHECK:
For the proper ignition voltage output with spark tester ST-125.
CHECK:
The spark plugs. Remove the spark plugs. Check them for, cracks, wear, improper gap, burned electrodes, or
heavy deposits. Repair or replace as necessary.
CHECK:
For bare or shorted wires.
FUEL SYSTEM
CHECK:
The fuel pump relay operation. The fuel pump should turn ON for 2 seconds when the ignition is turned ON. Use
CHART A-4.1.
CHECK:
The Fuel pressure, refer to CHART A-4.2 in Section 6C2-2A.
CHECK:
For contaminated fuel or incorrect fuel.
CHECK:
If the problem worsens in hotter temperatures, check for leaking injectors. Refer to CHART A-4.2 in Section
6C2-2A.
NOTE:
A faulty in-tank fuel pump check valve will allow the fuel in the lines to drain back to the tank after the engine is
stopped. To check for this condition, perform the fuel system diagnosis. Refer to CHART A- 4.2 in Section 6C2-
2A.
ADDITIONAL CHECKS
CHECK:
The exhaust backpressure. Refer to CHART A-13 "RESTRICTED EXHAUST CHECK" in Section 6C2-2A.
CHECK:
The IAC valve operation. Refer to CHART A-7.1 and CHART A-7.2 in Section 6C2-2A.
CHECK:
For a basic engine problem. Camshaft timing chain for being stripped or slipped, causing the valve timing to be
retarded.
CHECK:
The compression. Disconnect the ENGINE fuse before performing this test.
CHECK:
Service Bulletins for updates.
SURGES AND/OR CHUGGLES
DEFINITION:
Engine power variation under steady throttle or cruise, feels as if the vehicle speeds up and slows down with no
change in the acceleration pedal.
PRELIMINARY CHECKS
• Perform the careful visual checks as described at the start of this Section - "IMPORTANT PRELIMINARY
CHECKS".
• Make sure driver understands the transmission torque converter clutch, and the A/C compressor operation as
explained in the owner's manual.
• Time or kilometres since an engine tune-up has been performed. Refer to time/distance intervals in owner's
handbook.
SENSORS
CHECK:
The Oxygen Sensors. The Oxygen Sensors should respond quickly to different throttle positions. If it does not,
check the Oxygen Sensor for silicon or other contaminations from fuel, or use of improper RTV sealant. The
sensor may have a white, powdery coating and result in a high but false signal voltage (rich exhaust indication).
The PCM will then reduce the amount of fuel being delivered to the engine, causing a severe driveability
problem. Also, watch for a coolant leak contamination or cracking.
CHECK:
The MAF sensor for the proper operation. Refer to CHA RT A-6.1 "MAF OUTPUT CHECK" in Section 6C2-2A.
IGNITION SYSTEM
CHECK:
For the proper ignition voltage output using spark tester ST-125 or 7230.
CHECK:
The spark plugs. Remove the spark plugs, check for, cracks, wear, improper gap, burned electrodes, or heavy
deposits. Repair or replace as necessary. Also, check the spark plug wires.
CHECK:
The ignition secondary coil or wiring shorting to earth.
FUEL SYSTEM
CHECK:
For contaminated or incorrect fuel.
NOTE:
To determine if the condition is caused by a rich or lean sy stem, the car should be driven at the speed of the
complaint. Monitoring LT Fuel Trim and ST Fuel Trim will help identify a problem.
Lean - Long term fuel trim near +20%, refer to "Diagnostic Aids" of DTC 44 or DTC 64 in Section 6C2-2A.
Rich - Long term fuel trim near -20%, refer to "Diagnostic Aids" of DTC 45 or DTC 65 in Section 6C2- 2A.
CHECK:
The fuel pressure while the condition exists, refer CHART A-4.2 in Section 6C2-2A.
CHECK:
The in line fuel filter. Replace if the fuel filter is dirty or plugged.
CHECK:
For restricted fuel injectors.
ADDITIONAL CHECKS
CHECK:
The PCM earth circuits for being clean, tight and in their proper location.
CHECK:
The vacuum lines for splits, kinks, leaks and proper connections.
CHECK:
The generator output voltage. Repair if less than 9V or greater than 16 volts.
CHECK:
The speedometer reading on the instrument panel cluster with the speed reading on a Tech 2 scan tool.
CHECK:
The Service Bulletins for updates.
CHECK:
That the correct PROM was installed in the PCM.
CHECK:
For excessive exhaust backpressure, refer CHART A-13 "RESTRICTED EXHAUST CHECK" in Section 6C2-
2A.
CHECK:
The TCC for the proper operation.
LACK OF POWER, SLUGGISH, OR SPONGY
DEFINITION:
Engine delivers less than expected power. Little or no increase in speed when the accelerator pedal is pushed down
part way.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as described at start of this Section - "IMPORTANT PRELIMINARY
CHECKS".
• Compare the customer's car to a similar unit. Make sure the customer has an actual problem.
• Remove the air filter and check the air filter for dirt, or for a restriction. Replace as necessary.
• Time or kilometres since an engine tune-up has been performed. Refer to time/distance intervals in owner's
handbook.
SENSORS
CHECK:
The MAF sensor. Refer to CHART A-6.1 "MAF SENSOR OUTPUT CHECK" in Section 6C2-2A.
ENGINE MECHANICAL
CHECK:
The engine valve timing.
CHECK:
For a correct or worn camshaft.
CHECK:
The compression. Disconnect the "Engine" fuse, refer to Section 6A2 ENGINE MECHANICAL - V8 ENGINE,
before performing this test.
IGNITION SYSTEM
CHECK:
The secondary voltage using an oscilloscope or a spark tester ST-125 or 7230.
CHECK:
The engine for misfire under heavy engine load. Check each spark plug lead for excessive resistance, or for a
faulty or cracked spark plugs.
FUEL SYSTEM
CHECK:
For a restricted fuel filter. Refer to CHART A-4.2 in Section 6C2-2A.
CHECK:
The fuel pressure. Refer to CHART A-4.2 in Section 6C2-2A.
CHECK:
For contaminated fuel. Refer to CHART A-4.2 in Section 6C2-2A.
ADDITIONAL CHECKS
CHECK:
The PCM earth circuits for being clean, tight and in their proper locations.
CHECK:
The generator output voltage. Repair if less than 9 volts or greater than 16 volts.
CHECK:
The exhaust system for a restriction. Refer to CHART A-13 in Section 6C2-2A.
Inspect the exhaust system for a damaged or a collapsed pipe.
Inspect the muffler for heat distress or for internal damage.
CHECK:
The Torque Converter Clutch (TCC) for the proper operation.
DETONATION/SPARK KNOCK
DEFINITION:
A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with
throttle opening.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as described at start of this Section - " IMPORTANT PRELIMINARY
CHECKS".
NOTE:
If the 2 scan tool readings are normal (see "On-Board Diagnostic System Check") and there are no engine
mechanical faults, fill the fuel tank with a premium unleaded fuel and reevaluate the vehicle's performance.
IGNITION SYSTEM
CHECK:
The ignition base timing.
CHECK:
The spark plugs for the proper heat range.
ENGINE MECHANICAL
CHECK:
The combustion chambers for excessive carbon build up. Remove the carbon with top engine cleaner and follow
the instructions on the can. If the problem recurs and the top engine cleaner corrects the problem again, look for
the causes of high oil consumption.
CHECK:
For excessive oil in the combustion chamber.
Valve oil seals leaking.
CHECK:
The combustion chamber pressure by performing a compression test. Disconnect the "Engine" fuse, refer to
Section 6A2 ENGINE MECHANICAL - V8 ENGINE, before performing the test.
CHECK:
For the incorrect base engine parts such as camshaft, heads, pistons, etc.
COOLING SYSTEM
Check for engine overheating problems:
Low engine coolant.
A faulty engine thermostat.
A lose water pump belt.
Restricted air flow to radiator, or restricted water flow through radiator.
An inoperative electric cooling fan circuit. Refer to CHART A-12 in Section 6C2-2A.
The correct coolant solution should be a 50/50 mix of antifreeze coolant and water.
FUEL SYSTEM
CHECK:
The fuel quality for the proper octane rating.
NOTE:
To determine if the condition is caused by a rich or lean sy stem, the car should be driven at the speed of the
complaint. Monitoring the LT Fuel Trim will help identify the problem.
Lean - Long term fuel trim near + 20%, refer to "Diagnostic Aids" of DTC 44 or DTC 64 in Section 6C2-2A.
Rich - Long term fuel trim near - 20%, refer to the "Diagnostic Aids" of DTC 45 or DTC 65 in Section 6C2-2A.
CHECK:
The fuel pressure. Refer to CHART A-4.2 in Section 6C2-2A.
ADDITIONAL CHECKS
CHECK:
For vacuum leaks.
CHECK:
The TCC operation, the TCC applying too soon.
CHECK:
For the correct PROM in the PCM.
CHECK:
The Service Bulletins for updates.
HESITATION, SAG, STUMBLE
DEFINITION:
Momentary lack of response as the accelerator is pushed down. Can occur at all vehicle speeds. Usually most
severe when accelerating from a standing stop. May cause the engine to stall if severe enough.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as described at the start of this Section - " IMPORTANT
PRELIMINARY CHECKS".
• Time or distance interval since the normal engine tune-up has been performed. Refer to time/distance intervals
in the owner's handbook.
• The vacuum hoses for splits, kinks, and the proper connections.
• For vacuum leaks at the throttle body and at the intake manifold.
SENSORS
CHECK:
The TP Sensor - Check that the TP Sensor is not binding or sticking. The voltage should increase at a steady
rate as the throttle is being depressed. Refer to CHART A-6.2 in Section 6C2-2A.
CHECK:
The MAF sensor. Refer to CHART A-6.1 in Section 6C2-2A.
CHECK:
The engine coolant temperature sensor resistance. See Diagnostic Trouble Code 14 for the engine coolant
temperature sensor vs temperature resistance table.
IGNITION SYSTEM
CHECK:
The spark plugs for being fouled.
CHECK:
The spark plug wires. Check the resistance of the wires and for any physical damage.
CHECK:
The ignition system earth circuit.
FUEL SYSTEM
CHECK:
The fuel pressure. Refer to CHART A-4.2 in Section 6C2-2A.
CHECK:
For contaminated or incorrect fuel.
CHECK:
The canister purge system for the proper operation.
CHECK:
The fuel injectors. Perform the injector balance test.
ADDITIONAL CHECKS
CHECK:
The Service Bulletins for updates.
CHECK:
The exhaust system backpressure. Refer to CHART A-13 "RESTRICTED EXHAUST SYSTEM TEST" in
Section 6C2-2A.
CHECK:
The engine thermostat for the proper heat range.
CHECK:
The generator output voltage. Repair if less than 9 volts or more than 16 volts.
CUTS OUT, MI SSES
DEFINITION:
Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. The
exhaust has a steady spitting sound at idle or under load.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as described at the start of this Section - " IMPORTANT
PRELIMINARY CHECKS".
IGNITION SYSTEM
If the ignition system is suspected of causing a misfire at idle or cutting out under load.
CHECK:
Visually inspect the ignition system for moisture, dust, cracks, burns, etc. Spray the plug wires with a fine water
mist to check for shorts.
CHECK:
For a misfiring cylinder at idle by:
1. Starting the engine, then disconnecting the IAC motor. Remove one spark plug wire at a time using insulated
pliers. Do not run the engine for long periods with any of the spark plugs disconnected. The unburned fuel
causes the catalytic converter to be abnormally hot, and damage may occur if allowed to run too long.
2. If there is an RPM drop on all the cylinders (equal to within 50 RPM), go to ROUGH, UNSTABLE, OR
INCORRECT IDLE, STALLING Symptom Chart in this Section. Reconnect the IAC motor.
3. If there is no RPM drop on one or more cylinders, or there is an excessive variation in drop, check for spark on
the suspected cylinder(s) with an ST-125 Spark Checking tool or equivalent. If no spark, check the spark plug
lead for excessive resistance (or a possible `open') If there is spark, remove the spark plug(s) in those cylinders
and check for:
- Cracks - Wear
- Improper Gap - Burned Electrodes
- Heavy Deposits
ENGINE MECHANICAL
CHECK:
The compression. Perform a compression check on the questionable cylinder(s) found. If compression is low,
repair as necessary. Disconnect the "Engine" fuse, refer to Section 6A2 ENGINE MECHANICAL - V8 ENGINE,
before checking.
CHECK:
For a base engine problem. Remove the rocker covers. Check for bent pushrods, worn rocker arms, broken
valve springs, worn camshaft lobes and the valve timing, repair as necessary.
FUEL SYSTEM
CHECK:
The fuel system - Blocked fuel filter, low pressure, refer to CHART A-4.2 in Section 6C2-2A.
CHECK:
For contaminated or incorrect fuel.
CHECK:
The performance of the fuel injectors. If there is good spark and good compression on all the cylinders, check
for restricted or non-operating fuel injectors.
To check for a non-operating injector:
With the engine idling, check for a clicking sound at each injector with a stethoscope or long screwdriver held
on the body of each injector. If any injector fails to make the clicking sound, disconnect the electrical connector,
and connect a test light, across the harness connector terminals. If the test light blinks with the engine idling,
replace the injector. If there is no blinking light, check for an open wire leading to that injector.
ADDITIONAL CHECKS
CHECK:
For EMI interference. A missing condition can be caused by Electromagnetic Interference (EMI) on the reference
circuit. An EMI problem can usually be detected by monitoring the engine RPM with a Tech 2 scan tool. A
sudden increase in RPM with little change in the actual engine RPM change, indicates that EMI is present. If the
problem exists, check the routing of the secondary wires, also, check the earth circuit.
CHECK:
The inlet and the exhaust manifold passages for casting flash.
ROUGH, UNSTABLE, OR I NCORRECT IDLE, STALLING
DEFINITION:
The engine runs unevenly at idle. If bad enough, the vehicle may shake. Also, the idle may vary in RPM (called
"hunting"). Either condition may cause stalling. The engine will idle at an incorrect speed.
PRELIMINARY CHECKS
∙Perform the careful visual/physical checks as described at start of this Section - " IMPORTANT
PRELIMINARY CHECKS".
CHECK:
For vacuum leaks, they will cause a fast idle.
CHECK:
The PCM earths for being clean, tight and in there proper location refer Fig. 6C2-2B-1 at the beginning of this
Section.
CHECK:
The Idle Air Control (IAC) valve for proper operation. Refer to CHART A-7.1 IDLE AIR CONTROL SYSTEM in
Section 6C2-2A.
GNITION SYSTEM
CHECK:
For the proper ignition voltage output using spark tester ST-125 or 7230.
CHECK:
The spark plugs. Remove the spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes,
or heavy deposits.
ENGINE MECHANICAL
CHECK:
Perform a cylinder compression check. Disconnect the Engine fuse before checking.
CHECK:
For camshaft valve lift and timing, and for weak valve springs.
FUEL SYSTEM
CHECK:
For contaminated or incorrect fuel.
CHECK:
For fuel injectors that are restricted or not operating.
CHECK:
For fuel injectors leaking, or incorrect fuel pressure. Refer to CHART A-4.2 in Section 6C2-2A.
NOTE:
Monitoring the long term fuel trim will help identify the cause of the problem. If the system is running lean (Long
Term Fuel Trim near + 20%), refer to "Diagnostic Aids" of DTC 44 or DTC 64. If the system is running rich
(Long Term Fuel Trim near - 20%), refer to "Diagnostic Aids" of DTC 45 or DTC 65 in Section 6C2-2A.
CHECK:
For fuel in the pressure regulator hose. If fuel is present, replace the fuel pressure regulator assembly.
CHECK:
The Oxygen Sensor- the O2 sensor should respond quickly to different throttle positions. If the O2 sensor
respond quickly check the O2 sensor for silicon contamination from fuel, or the use of improper RTV sealant.
The O2 sensor will have a white, powdery coating, and will result in a high but false signal voltage (rich exhaust
indication). The PCM will then reduce the amount of fuel being delivered to the engine, causing a severe
driveability problem.
ADDITIONAL CHECKS
CHECK:
The MAF sensor. Refer to CHART A-6.1 in Section 6C2-2A.
CHECK:
The throttle linkage for sticking or binding.
CHECK:
The IAC valve operation. Refer to CHART A-7.1 in Section 6C2-2A.
CHECK:
The A/C signal to the PCM. The Tech 2 scan tool should show that A/C is being requested whenever the A/C is
selected and the blower switch is ON. If the problem still exists with the A/C ON, check the A/C system operation
CHART A-11.1 or CHART A-11.3 in Section 6C2-2A.
CHECK:
The PCV valve for the proper operation. Place a finger over the inlet hole the PCV valve end several times. The
PCV valve should snap back. If not, replace the PCV valve.
CHECK:
The Service Bulletins for updates.
CHECK:
For broken motor mounts.
CHECK:
The generator output voltage. Repair the generator if the voltage is less than 9 volts or greater than 16 volts.
CHECK:
The battery cables and earth straps. They should be clean and secure. Erratic voltage will cause the IAC valve to
change positions resulting in poor idle quality.
POOR FUEL ECONOMY
DEFINITION:
Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, economy is noticeably
lower than it was on this vehicle at one time, as previously shown by an actual road test.
A misfiring engine will have excessive unburned oxygen in the exhaust, and the oxygen sensor will detect a lean
exhaust. The PCM will command an increase in the fuel injector pulsewidth in an attempt to overcome the lean
exhaust condition.
PRELIMINARY CHECKS
• Perform the careful visual checks as described at start of this Section - " IMPORTANT PRELIMINARY
CHECKS".
• Visually/physically check: The vacuum hoses for splits, kinks, and proper connections
• Check the owner's driving habits:
- Is the A/C ON full time (Defroster mode ON)?
- Are the tyres at the correct pressure?
- Are excessively heavy loads being carried?
- Is acceleration too much, too often?
• Check the air cleaner element (filter) for being dirty or being plugged.
• Check for the correct size tyres. Oversize tyres will cause the speedometer/odometer to be slow, and the
indicated fuel usage may increase.
IGNITION SYSTEM
CHECK:
The spark plugs. Remove the spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes,
or heavy deposits. Repair or replace as necessary.
COOLING SYSTEM
CHECK:
The engine coolant level.
CHECK:
The engine thermostat for being stuck open or for the wrong heat range.
ENGINE MECHANICAL
CHECK:
The Compression. Disconnect the “Engine” fuse, refer to Section 6A2 ENGINE MECHANICAL - V8 ENGINE,
before checking.
ADDITIONAL CHECKS
CHECK:
The TCC operation. A Tech 2 scan tool should indicate an RPM drop, when the TCC is commanded ON.
CHECK:
For dragging brakes.
CHECK:
For an exhaust system restriction, refer to CHART A-13 in Section 6C2-2A.
CHECK:
For the proper calibration of the speedometer.
CHECK:
The induction system and crankcase for air leaks.
BACKFIRE
DEFINITION:
The fuel ignites inside the intake manifold, or in exhaust stream, making a loud popping noise.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as described at start of this Section - " IMPORTANT PRELIMINARY
CHECKS".
IGNITION SYSTEM
CHECK:
For the proper ignition coil output voltage with a spark tester ST-125 or 7230.
CHECK:
The spark plugs. Remove the spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes,
heavy deposits. Repair or replace the spark plugs as necessary.
CHECK:
Spark plug wires for crossfire, also inspect the distributor assembly, the spark plug wires, and the proper routing
of the plug wires.
ENGINE MECHANICAL
CHECK:
The compression - Look for sticking or leaking valves. Remove the "Engine" fuse, refer to Section 6A2
ENGINE MECHANICAL - V8 ENGINE, before performing the checking.
CHECK:
The valve timing.
CHECK:
The intake manifold and exhaust manifold passages for casting flash.
FUEL SYSTEM
CHECK:
Perform The "Fuel System Diagnosis Check". Refer to CHART A-4.2 in Section 6C2-2A.
EXCESSIVE EXHAUST EMISSIONS OR ODOURS
DEFINITION:
The vehicle fails an emission test. The vehicle has an excessive rotten egg smell. Excessive odours do not
necessarily indicate excessive emissions.
PRELIMINARY CHECKS
• Perform the " On-Board Diagnostic System Check" in Section 6C2-2A.
IGNITION SYSTEM
CHECK:
The spark plugs. Remove the spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or
heavy deposits. Repair or replace any spark plugs as necessary.
COOLING SYSTEM
If the Tech 2 scan tool indicates a very high engine coolant temperature and the system is running lean:
CHECK:
The engine coolant level.
CHECK:
The engine thermostat for a faulty part or for the wrong heat range.
CHECK:
The cooling fan operation.
FUEL SYSTEM
CHECK:
For contaminated or incorrect fuel.
NOTE:
If the system is running RICH (Long Term Fuel Trim near -13%) - Refer to "Diagnostic Aids" of DTC 45 or a
DTC 65 in Section 6C2-2A. If the system is running LEAN (Long Term Fuel Trim near +18%) - Refer to
"Diagnostic Aids" of DTC 44 or DTC 64 in Section 6C2-2A.
CHECK:
For a properly installed fuel cap.
CHECK:
The fuel pressure. Refer to CHART A-4.2 in Section 6C2-2A.
CHECK:
The canister for fuel loading.
ADDITIONAL CHECKS
CHECK:
For vacuum leaks.
CHECK:
For burnt valves.
CHECK:
For lead contamination in the catalytic converter (look for the removal of the fuel filler neck restricter).
CHECK:
For carbon build-up. Remove the carbon with top engine cleaner. Follow the instructions on the can.
CHECK:
For an exhaust system restriction. Refer to CHART A-13 in Section 6C2-2A.
CHECK:
The PCV valve for being plugged or stuck.
CHECK:
For fuel in the crankcase.
CHECK:
The Service Bulletins for updates.
DIESELING, RUN-ON
DEFINITION:
Engine continues to run after the ignition is turned OFF, and runs very rough.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as described at start of this Section - " IMPORTANT PRELIMINARY
CHECKS".
FUEL SYSTEM
CHECK:
The fuel injectors for leakage. Perform the "Fuel System Diagnosis Check". Refer to CHART A-4.2 in Section
6C2-2A.
IGNITION SYSTEM
CHECK:
If the engine runs smoothly, check the ignition switch and the adjustment.
RICH/LEAN SYMPTOM CHART
CIRCUIT DESCRIPTION
The Rich/Lean Symptom Chart is an organised approach in identifying a driveability complaint that may be caused
by an overrich or overlean operating condition. Understanding the chart and using it correctly will reduce diagnostic
time and improve customer satisfaction. Start at the left side of the chart and work to the right.
TEST DESCRIPTION:
Numbers below refer to step number(s) on the diagnostic chart.
1. This is a partial list of the possible customer complaints. and what the air/fuel mixture must be to cause such a
condition.
2. A lean exhaust means that there is a lot of oxygen in the exhaust stream. Lots of oxygen in the exhaust stream
produces a low oxygen sensor signal voltage. A rich exhaust means that there is a lot of fuel and very little
oxygen in the exhaust stream.
3. The oxygen sensor signal to the PCM determines what the PCM should do to compensate for the present
condition. Depending upon the severity of the problem, the PCM will compensate for the condition by changing
the short term fuel trim and the short term fuel trim values either higher or lower. A short term fuel trim value
above 0% means the PCM will add more fuel to the engine. The PCM will increase the injector pulse width,
thus making a lean engine run richer. A short term fuel trim value below 0% means the PCM will decrease the
amount of fuel to the engine. The PCM decreases the injector pulse width, thus making a rich engine run
leaner.
4. This list contains areas where you should look to find the root cause of the customer complaint. Not every
cause of the symptom is listed here. The items listed provide a good general description of areas to look.
DIAGNOSTIC AIDS
Driveability complaints may be caused by the PCM, the system components, or electrical faults. A basic engine
problem may have a symptom similar to an electrical fault. Check the air cleaner and all the basic engine
components. There could be worn rings, worn camshaft lobes, collapsed lifters, misaligned timing chain, or vacuum
leaks, etc.
AUTOMATIC TRANSMISSION SYMPTOM CHARTS
OIL PRESSURE HIGH OR LOW
CHECKS CAUSES
Oil Pump Assembly • Pressure regulator valve stuck
• Pressure regulator valve spring
• Rotor guide omitted or disassembled
• Rotor cracked or broken
• Reverse boost valve or sleeve stuck, damaged or incorrectly
assembled
• Orifice hole in pressure regulator valve plugged
• Sticking slide or excessive rotor clearance
• Pressure relief ball not seated or damaged
• Porosity in pump cover or body
• Wrong pump cover
• Pump faces not flat
• Excessive rotor clearance
Oil Filter • Intake pipe restricted by casting flash
• Cracks in filter body or intake pipe
• O-ring seal missing, cut or damaged
• Wrong grease used on rebuild
Valve Body • Manual valve scored or damaged
• Spacer plate or gaskets incorrect, misassembled or
damaged
• Face not flat
• 2-3 Shift solenoid stuck
• Checkballs omitted or misassembled
Pressure Control
Solenoid Valve Damage to pins
TFP Val Position Sw. • Contamination
• Damaged seals
Case Case to valve body face not flat
HARSH SHIFTS
CHECKS CAUSES
Throttle Position
Sensor Open or shorted circuit
Vehicle Speed Sensor Open or shorted circuit
TFP Val Position Sw. • Contamination
• Damaged seals
Trans Fluid
Temperature Sensor Open or shorted circuit
Engine Coolant
Temperature Sensor Open or shorted circuit
Pressure Control
Solenoid Valve • Damage to pins
• Contamination
INACCURATE SHIFT POINTS
CHECKS CAUSES
Oil Pump Assembly • Stuck pressure regulator valve
• Sticking pump slide
Valve Body Assembly Spacer plate or gaskets misassembled, damaged or incorrect
Case • Porous or damaged valve body pad
• 2-4 Servo Assembly:
- 2-4 accumulator porosity
- Damaged servo piston seals
- Apply pin damaged or improper length
2-4 Band Assembly:
- Burned
- Anchor pin not engaged
TP Sensor • Disconnected
• Damage
Vehicle Speed Sensor • Disconnected
• Damaged
• Bolt not tightened
1ST GEAR RANGE ONLY-NO UPSHIFT
CHECKS CAUSES
Valve Body • The 1-2 Shift valve is sticking
• The spacer plate (48) or gaskets (47, 52) are mispositioned
or damaged
Case The case to valve body face is damaged or is not flat
Shift Solenoid Valves • Stuck or damaged
• Faulty electrical connection
2-4 Servo Assembly • The apply passage case is restricted or blocked
• Nicks or burrs on the servo pin or on the pin bore in the case
• Fourth servo piston is installed backwards
2 -4 Band Assembly ) • The 2-4 band is worn or damaged
• The band anchor pin is not engaged
SLIPS IN 1ST GEAR
CHECKS CAUSES
Forward Clutch
Assembly • Clutch plates worn
• Porosity or damage in forward clutch piston
• Forward clutch piston inner and outer seals missing, cut or
damaged
• Damaged forward clutch housing
• Forward clutch housing retainer and ball assembly not
sealing or damaged
Forward Clutch
Accumulator • Piston seal missing, cut or damaged
• Piston out of its bore
• Porosity in the piston or valve body
• Stuck abuse valve
Input Housing and
Shaft Assembly Turbine shaft seals missing, cut or damaged
Valve Body • 1-2 Accumulator valve stuck
• Face not flat, damaged lands or interconnected passages
• Spacer plate or gaskets incorrect, mispositioned or
damaged
Low Roller Clutch • Damage to lugs to inner ramps
• Rollers not free moving
• Inadequate spring tension
• Damage to inner splines
• Lube passage plugged
Torque Converter Stator roller clutch not holding
1-2 Accumulator
Assembly • Porosity in piston or 1-2 Accumulator cover and pin
assembly
• Damaged ring grooves on piston
• Piston seal missing, cut or damaged
• Valve body to spacer plate gasket at 1-2 Accumulator cover,
missing or damaged
• Leak between piston and pin
• Broken 1-2 Accumulator spring
Line Pressure Refer to Oil Pressure High or Low
2-4 Servo Assembly 4th Servo piston in backward
SLIPPING OR ROUGH 1-2 SHIFT
CHECKS CAUSES
Valve Body Assembly • 1-2 Shift solenoid train stuck
• Gaskets or spacer plate incorrect, mispositioned or
damaged
• 1-2 Accumulator valve stuck
• Face not flat
2-4 Servo Assembly • Apply pin too long or too short
• 2nd servo apply piston seal missing, cut or damaged
• Restricted or missing oil passages
• Servo bore in case damaged
2nd Accumulator • Porosity in 1-2 accumulator housing or piston
• Piston seal or groove damaged
• Nicks or burrs in 1-2 accumulator housing
• Missing or restricted oil passage
2-4 Band Worn or mispositioned
Oil Pump Assembly or
Case Faces not flat
NO 2-3 SHIFT OR 2-3 SHIFT SLIPS, ROUGH OR HUNTING
CHECKS CAUSES
Valve Body Assembly • 1-2 Shift valve train stuck
• Gaskets or spacer plate incorrect, mispositioned or
damaged
• 1-2 Accumulator valve stuck
• Face not flat
2-4 Servo Assembly • Apply pin too long or too short
• 2nd servo apply piston seat missing, cut or damaged
• Restricted or missing oil passages
• Servo bore in case damaged
2nd Accumulator • Porosity in 1-2 accumulator housing or piston
• Piston seal or groove damaged
• Nicks or burrs in 1-2 accumulator housing
• Missing or restricted oil passage
2-4 Band Worn or mispositioned
Oil Pump Assembly or
Case Faces not flat
2ND/3RD GEARS ONLY OR 1ST/4TH GEARS ONLY
CHECKS CAUSES
Shift Solenoid • Sediment is in the valves
• The electrical connection is faulty
• Damaged seal
THIRD GEAR ONLY
CHECKS CAUSES
DTC 81 • The electrical connection is faulty
• Shorted or damaged
3-2 FLARE OR TIE-UP
CHECKS CAUSES
3-2 Shift Solenoid • Shorted or damaged
• Contamination
• Damaged Seal
NO 3-4 SHIFT, SLIPS OR ROUGH 3-4 SHIFT
CHECKS CAUSES
Oil Pump Assembly • Pump cover retainer and ball assembly omitted or damaged
• Faces not flat
Valve Body Assembly • Valves stuck:
- 2-3 Shift solenoid train
- Accumulator valve
- 1-2 Shift solenoid train
- 3-2 shift solenoid
• Spacer plate or gaskets incorrect, mispositioned or
damaged
2-4 Servo Assembly • Incorrect band apply pin
• Missing or damaged servo seals
• Porosity in piston, cover or case
• Damaged piston seal grooves
• Plugged or missing orifice cup plug
Case • 3rd Accumulator retainer and ball assembly leaking
• Porosity in 3-4 accumulator piston or bore
• 3-4 Accumulator piston seal or seal grooves damaged
• Plugged or missing orifice cup plug
• Restricted oil passage
Input Housing
Assembly Refer to Slipping 2-3 Shift
2-4 Band Assembly Worn or Disassembled
NO REVERSE OR SLIPS IN REVERSE
CHECKS CAUSES
Input Housing
Assembly • 3-4 Apply ring stuck in the applied position
• Forward clutch not releasing
• Turbine shaft seals missing, cut or damaged
Manual Valve Link Disconnected
Valve Body Assembly • 2-3 Shift solenoid stuck
• Manual linkage not adjusted
• Spacer plate and gaskets incorrect, mispositioned or
damaged
• Lo overrun valve stuck
• Orificed cup plug restricted, missing or damaged
Reverse Input Clutch
Assembly • Clutch plate worn
• Reverse input housing and drum assembly cracked at weld
• Clutch plate retaining ring out of groove
• Return spring assembly retaining ring out of groove
• Seals cut or damaged
• Restricted apply passage
• Porosity in piston
• Belleville plate installed incorrectly
• Excessive clutch plate travel
• Oversized housing
Lo and Reverse Clutch • Clutch plates worn
• Porosity in the piston
• Seals damaged
• Return spring assembly retaining ring mispositioned
• Restricted apply passage
NO PART THROTTLE OR DELAYED DOWNSHIFTS
CHECKS CAUSES
Input Housing
Assembly • 3-4 Apply ring stuck in applied position
• Forward clutch not releasing
• Turbine shaft seals missing, cut or damaged
Manual Valve Link Disconnected
Valve Body Assembly • 2-3 Shift solenoid stuck
• Manual linkage not adjusted
• Spacer plate and gaskets incorrect, mispositioned or
damaged
• Lo overrun valve stuck
• Orificed cup plug restricted, missing or damaged
Reverse Input Clutch
Assembly • Clutch plate worn
• Reverse input housing and drum assembly cracked at weld
• Clutch plate retaining ring out of groove
• Return spring assembly retaining ring out of groove
• Seals cut or damaged
• Restricted apply passage
• Porosity in piston
• Belleville plate installed incorrectly
• Excessive clutch plate travel
• Oversized housing
Lo and Reverse Clutch • Clutch plates worn
• Porosity in piston
• Seals damaged
• Return spring assembly retaining ring mispositioned
• Restricted apply passage
HARSH GARAGE SHIFT
CHECKS CAUSES
Valve Body Assembly • Orifice cup plug missing
• Checkball missing
NO OVERRUN BRAKING - MANUAL 3-2-1
CHECKS CAUSES
External Linkage Not adjusted properly
Valve Body Assembly • 4-3 Sequence valve stuck
• Checkball mispositioned
• Spacer plate and gaskets incorrect, damaged or
mispositioned
Input Clutch Assembly • Turbine shaft oil passages plugged or not drilled
• Turbine shaft seal rings damaged
• Turbine shaft sealing balls loose or missing
• Porosity in forward or overrun clutch piston
• Overrun piston seals cut or damaged
• Overrun piston checkball not sealing
NO TCC APPLY
CHECKS CAUSES
Electrical • 12 Volts not supplied to transmission
• Outside electrical connector damaged
• Inside electrical connector, wiring harness or solenoid
damaged
• Electrical short (pinched solenoid wire)
• Solenoid not earthed
Converter Internal damage
Oil Pump Assembly • Converter clutch valve stuck or assembled backwards
• Converter clutch valve retaining ring mispositioned
• Pump to case gasket mispositioned
• Orifice cup plug restricted or damaged
• Solenoid O-ring seal cut or damaged
• High or uneven bolt torque (pump body to cover)
Input Housing and
Shaft • Turbine shaft O-ring seal cut or damaged
• Turbine shaft retainer and ball assembly restricted or
damaged
TFP Val Position
Switch • Contamination
• Damaged seals
Valve Body Assembly • TCC signal valve stuck
• Solenoid O-ring leaking
Solenoid Screen Blocked
TCC Solenoid Valve —
Engine Speed Sensor —
Engine Coolant
Temperature Sensor —
DTCs 19, 21, 22, 28,
67, 81, 83, 84 —
Automatic
Transmission Fluid
Temperature Sensor
—
TORQUE CONVERTER CLUTCH SHUDDER
CHECKS CAUSES
Electrical • 12 Volts not supplied to transmission
• Outside electrical connector damaged
• Inside electrical connector, wiring harness or solenoid
damaged
• Electrical short (pinched solenoid wire)
• Solenoid not earthed
Converter Internal damage
Oil Pump Assembly • Converter clutch valve stuck or assembled backwards
• Converter clutch valve retaining ring mispositioned
• Pump to case gasket mispositioned
• Orifice cup plug restricted or damaged
• Solenoid O-ring seal cut or damaged
• High or uneven bolt torque (pump body to cover)
Input Housing and
Shaft • Turbine shaft O-ring seal cut or damaged
• Turbine shaft retainer and ball assembly restricted or
damaged
TFP Val Position
Switch • Contamination
• Damaged seals
Valve Body Assembly • TCC signal valve stuck
• Solenoid O-ring leaking
Solenoid Screen Blocked
NO TCC RELEASE
CHECKS CAUSES
TCC Solenoid Valve • Internal earth
• Clogged exhaust orifice
Converter Internal damage
Valve Body Assembly The converter clutch enable valve is stuck in the apply position
Oil Pump Assembly The converter clutch valve is stuck
PCM External earth
DRIVES IN NEUTRAL
CHECKS CAUSES
Forward Clutch The clutch does not release
Manual Valve Link Disconnected
Case • The face is not flat
• Internal leakage exists
2ND GEAR START
CHECKS CAUSES
Forward Clutch Sprag
Assembly The sprag assembly is installed backwards
NO PARK
CHECKS CAUSES
Parking Linkage • Actuator rod assembly bent or damaged
• Actuator rod spring binding or improperly crimped
• Actuator rod not attached to inside detent lever
• Parking lock bracket damaged or not torqued properly
• Inside detent lever not torqued properly
• Parking pawl binding or damaged
OIL OUT THE VENT
CHECKS CAUSES
Oil Pump Chamber in pump body rotor pocket
Miscellaneous Fluid level -overfilled
VIBRATION IN REVERSE AND WHINING NOISE IN PARK
CHECKS CAUSES
Oil Pump Chamber in pump body rotor pocket
Miscellaneous Fluid level -overfilled
RATCHETING NOISE
CHECKS CAUSES
Parking Pawl The parking pawl return spring is weak, damaged, or
misassembled
NO DRIVE IN ALL RANGES
CHECKS CAUSES
Torque Converter The converter to flex plate bolts are missing
NO DRIVE IN DRIVE RANGE
CHECKS CAUSES
Torque Converter • The stator roller clutch is not holding
• The converter is not bolted to the flex plate
FRONT OIL LEAK
CHECKS CAUSES
Torque Converter • The welded seam is leaking
• The converter hub is damaged
Torque Converter Seal • The seal assembly is damaged
• The garter spring is missing
DELAY IN DRIVE AND REVERSE
CHECKS CAUSES
Torque Converter Converter drainback
PCM CONNECTOR SYMPTOM CHARTS
A Powertrain Control Module (PCM) connector Symptoms Chart identifies the function of each pin to and from the
PCM connector, the circuit number, the wire colour, and the cavity of the component to which the wire connects.
The left column lists the PCM connector pins in ascending order. The chart may also be entered from the right-most
column, which lists possible symptoms that may be caused by a fault in each of the circuits. A problem in any of
these circuits will cause a Diagnostic Trouble Code to set. The DTC's are identified in the second column from the
right edge of the chart. (However, if a DTC has been set, you should attempt to diagnose the condition using
Section 6C2-2A. The expected normal voltage for each circuit is shown for two conditions. One check is with the
ignition "ON" engine “OFF”, and the other check is with the engine running. Both checks are required for accurate
diagnosis. Reference notes are made for some circuits. These notes state the conditions that cause the varying
voltages or mention unique characteristics of the circuit. To measure the voltages, backprobe the PCM connector.
Whenever backprobing, be careful not to damage the connector. Careless backprobing may damage the connector
seal and/or terminal. Damaged pins will provide incorrect readings and cause additional system problems.
PCM CONNECTOR A
PCM CONNECTOR B
PCM CONNECTOR C
PCM CONNECTOR D
PCM CONNECTOR E
PCM CONNECTOR F
TESTING EARTHS
Unusual displays on the instrument cluster, lamps
that are dim or flash unexpectedly, unusual Tec h 2
readings - are classic symptoms of earth problems.
This section discusses the importance of good
earth circuits. This section starts by explaining
some basic theories. Then you are shown how to
diagnose a solid-state circuit earth condition. If
there is a problem, it will direct you on how to
correct the condition.
BASICS
For a circuit to operate properly, you need three
things - a good power supply to the component, a
good component and a good earth. Circuits are
complete systems. Current must flow from
beginning to end as designed.
Some technicians have dif ficulty visualising why an
earth circuit must be free of unwanted resistance.
The current passes in and out of a component like
water flowing through a tube. With a properly
draining tube, the water can flow out as freely as it
flows in. Current must enter and leave the
components freely, if they are to perform as
designed.
High current devices can cause voltage spikes
when turned ON or OFF. To prevent these spikes
from affecting sensitive solid-state circuits, high
currr ent devices use a s eparate earth location. T he
use of a dedicated circuit connected to an isolated
earth junction block and then to the battery
negative terminal reduces the effect of spikes on
sensitive c ircuits . Solid-state circ uits are par ticularly
sensitive to poor circuit continuity because in most
cases they use low current. This section on earths
concerns with one solid-s tate devic e, the PCM. T he
information included here applies to all solid-state
earth circuits.
Severe restrictions in the earth circuit can cause
resets and intermittent codes to set. The PCM
receives inputs from low voltage sensors. This
includes the Mass Air Flow sensor, the crankshaft
position, the TP sensor etc. The PCM then
operates output devices (fuel injectors, idle air
control, etc.) These input and output devices need
good continuity for correct operation.
A misadjusted or faulty sensor can cause the
sensor values to shift, causing driveability
problem s. If there is an excessive resistance in the
earth circuit, the result will be the same; shifted
sensor outputs with corresponding driveability
conditions. These conditions may not be severe
enough to set diagnostic trouble codes, but they will
reduce the vehicle performance
Figure 6C2-2B-2
Sensor circuit earth sensitivity - an example.
Looking at the Throttle Position (TP) sensor circuit
will provide an example of how any resistance in
the earth circuit can cause problems. The
accompanying figure (Figure 6C2-2B-3) shows a
throttle position sens or first with a good earth circ uit
and then with a poor connection in the earth cir cuit.
Refer to this figure as you proceed through the tex t
that follows.
A throttle position sensor consists of a resistor and
a wiper. One terminal of the resistor is connected to
a reference voltage and the other terminal is
connected to an earth. As the wiper moves along
the resistor, the voltage of the wiper terminal
changes. If the wiper is near the reference voltage
end of the resistor, the wiper output will approach
the supply voltage (over 4.5 volts at wide open
throttle). As the wiper moves toward the earthed
end of the resistor the voltage of the wiper output
decreases to near zero (about 0.5 volts for the
closed throttle in this example). The actual closed
and wide open throttle voltage specifications may
vary for different engines. The TP sensor output
should never be supply voltage or zero volts.
Figure 6C2-2B-3 shows voltage drops across
various points in the circuit. In the example with a
good earth circuit, the T P sensor is shown with the
wiper in the closed throttle position. The total
voltage across the resistor in the TP sensor is 5
volts. The voltage drop from the resistor source
voltage terminal to the wiper is 4.5 volts. The
voltage drop from the wiper to the resistor earth
side is 0.5 volts. The wiper output is 0.5 volts - a
good value for this example of a closed throttle.
Look at the TP sensor with the bad signal caused
by resistance in the earth circuit. The throttle
positions stays the same but the sensor's output
voltage changes. The increased resistance causes
an additional voltage drop of 0.5 volts. The voltage
drop from the wiper to earth is now 1.0 volt (0.5 +
0.5 = 1.0). Because the source voltage is a
constant 5 volts, the voltage drop from the source
voltage input to the wiper can now be only 4 volts
(5.0 - 1.0 = 4.0). The PCM now receives 1.0 volt
from the TP sensor. This is not a good value (in
this example) of a closed throttle.
Figure 6C2-2B-3
EARTH CIRCUITS
Section 12P, WIRING DIAGRAMS should be
used whenever you are diagnosing any electrical
condition, including earths. The individual circuits
show the power and earth circuits for components
in specific systems.
If you suspect several c ircuits are being af fec ted by
a poor earth circuit, look at the circuits to see how
the systems might interact. If they have any
common earth wires, begin your diagnosis there.
Back-feeding is when current, seeking earth, feeds
back through inactive circuits (the reverse direction
of normal current flow) to find a path to earth. This
can only happen when the active circuit (needing
an earth) shares a disconnected or poor earth with
an inactive circuit and the voltage supply side of the
inactive circuit feeds other components with good
earths.
PARALLEL EARTHS
Some solid-state components use redundant earth
circuits. The PCM has more than one earth circuit.
There are several reasons for the redundant
earths.
The PCM has many low-current circuits, but the
current from all these circuits (when they are
active) add up to a larger current. Higher current
loads are managed more easily with several regular
size wires, rather than with one large diam eter wire.
Basic circuit theory shows that the effective
resistance of parallel resistors is less than any of
the individual resistors. T his is tr ue even for a sm all
resistances in wires. Parallel wires provide the
lowest resistance. In many solid-state systems a
problem with one of the ear th wires does not aff ect
the circuit. The redundant wires will handle the
current load. For other solid-state systems the loss
of even one redundant earth may affect the
operation, but the remaining earth wire(s) may
allow the vehicle to be driven.
Here is an example which can be difficult to a
driveability technician. Symptom:. Whenever a
Tech 2 scan tool is connected to the DLC and the
vehicle is being tested, none of the complaint
symptoms are displayed.
Cause: The PCM earths are not providing a good
earth, hence the resulting driveability condition.
When a Tech 2 scan tool is connected, a good
earth path is provided to the PCM through the Data
Link Connector (DLC). The DLC uses a different
earth than the PCM. Always test for driveability
symptom s before hooking up a Tec h 2 scan tool. If
they disappear when the Tech 2 scan tool is
connected, check the earth circuit for continuity.
The severity of the symptom(s) is proportional to
the severity of the problem in the earth circuit. A
open in the circuit has the most severe effect. Use
the severity of the symptom(s) as an indication of
the extent of the open in the earth circuit.
1 1 1 1
——— = ——— = ——— = ———
R R R 2 R 3
EXAMPLE: TWO PARALLEL CIRCUITS, ONE
WITH ONE OHM RESISTANCE AND
THE OTHER WITH TWO OHMS
RESISTANCE.
1 1 1
——¾ = ——¾ = ——¾
R Total 1W 2W
1 2 1
¾¾¾ = ¾¾¾ = ¾¾¾
R Total 2 2
1 3
¾¾¾ = ¾¾¾
R Total 2
2
R Total = ¾¾ W
3
CHECKING EARTHS
The bes t way to check f or a poor ear th connection in a solid-s tate circuit is to c heck f or a voltage drop. Use a high-
impedance voltmeter rated at a minimum of 10 megohms (10,000,000 ohms) per volt. Most quality digital
mu ltimeters meet or exceed this s pecification. Voltm eters with less impedanc e can af fect a circ uit and als o give an
incorrect reading.
With a voltmeter set on the 2 volt DC s cale, c onnect the black negative lead to the battery negative terminal. ( If you
are using an auto-ranging meter, set the meter to the DC volts setting. Connect the red positive lead to the earth
term inal of the com ponent to be tested. With the circ uit enabled, check the voltage drop in the circuit. If the voltage
reading is within the specifications, look for a cause other than a poor earth at this component.
If the voltage reading is too high, proceed by isolating the cause of the high voltage dr op. Move the positive lead to
the next connection in the ear th circ uit. (Keep the negative lead connected to the batter y negative term inal.). Check
both sides of each in-line connector and both the eyelet and the stud or screw at the earth points. Repeat this
process through the earth path until the voltmeter reading is within the specifications. The high resistance causing
the earth problem is located between where you obtained a good reading and the last high reading.
When a circuit uses redundant earths, check all the earths circuits for an excessive voltage drop.
SOLID-STATE CIRCUIT VOLTAGE DROP SPECIFICATIONS
There are two acceptable maximum voltage drops for solid-state circuits. If you are measuring the voltage drop of a
circuit that will pass through a solid-state component before going to earth (such as the TP sensor circuit between
the TP sensor and the PCM), measured voltage cannot be higher than 0.060 volts (60 millivolts).
If you measure the voltage drop of a solid-state earth circuit anywhere in the earth path at or after the solid-state
component (such as the PCM earth circuit from the PCM to the battery), the maximum allowable voltage is 0.020
volts (20 millivolts). If you measure a voltage above the specifications, repair the earth circuit.
throttle position sensor circuit. Connect the voltmeter negative lead to the negative battery terminal. Turn the ignition
to the RUN position. Check the voltages at the various points between the TP sensor pin "B" and PCM terminal
"E16". A voltage reading of 0.060 volts or less with the meter positive lead at the TP sensor pin "B" terminal
indicates that the entire earth circuit from the TP sensor to the battery is continuous and sufficiently low in
resistance. A voltage reading of 0.060 volts at the splice or the PCM terminal "E16" pin would be wi thin
specifications.
When the voltage readings are taken in the earth circuit after the PCM, the specification changes. A voltage reading
of 0.020 volts (20 millivolts) or less is within specification. If the voltage is not within the specification, check the
different connectors to find the excess voltage. Check both sides of the in-line connectors and both the eyelets and
the stud at the earth points.
Figure 6C2-2B-5 Testing Voltage Drop Before the PCM
Figure 6C2-2B-6 Testing For A Voltage Drop After the PCM
EARTH CREDIBILITY CHECK
CIRCUIT DESCRIPTION:
The earth credibility check should be used at the beginning of all diagnostic procedures. The Earth Credibility Check
can also be used when no diagnostic trouble codes are set, and a symptom still exists.
TEST DESCRIPTION:
Number(s) below refer to number(s) on the diagnostic chart.
1. To test the voltage drop of the PCM system earth, a load must be present on the circuit. Putting the PCM in the
field service mode you energise most of the PCM circuits such as the check powertrain lamp control, cooling fan
relay, etc. If this test passes, continue using the symptoms charts to diagnosis the problem.
2. Check the connectors in the earth circuit to find the excessive voltage. Check both sides of the in-line
connectors.
DIAGNOSTIC AIDS:
Because the PCM operates on little current even minor corrosion will cause problems. Make sure the earths are
clean and tight. A good earth is about 25% of the total system circuit. Normally you will check the wiring for the
following conditions:
• Power
• Continuity
• Load
The PCM system earths are very important for proper operation.
STEP ACTION VALUE YES NO
1
Was the "On -Board
Diagnostic" (OBD) System
Check performed?
Go to Step 2 Go to the OBD
System Check.
Refer to
Section 6C2-2A
21. Ignition OFF.
2. Disconnect the Intake
Air Temperature (IAT)
sensor electrical
connector.
3. Use a digital volt/ohm
meter (DVM) set to DC
voltage.
4. Connect the negative
lead of the DVM to the
negative battery
terminal and connect
the positive lead to the
earth circuit at the IAT
sensor connector.
5. Ignition ON engine
OFF.
6. Install a Tech 2 scan
tool.
7. Using the Tech 2 scan
tool, enable the field
service mode.
Is the voltage reading on
the DVM less than the
specified value?
0.060
volts
(60 mV)
No problem
found, continue
with symptom
diagnosis.
Go to Step 3
3Remove and thoroughly
clean the PCM earth
terminals and the
connection.
Is the action complete?
Verify Repair
CORRECTING THE PROBLEMS IN THE EARTH CIRCUITS
Once a high resistance condition in an earth circuit has been located, you must determine the actual cause.
If the problem is at a connector, check for a bent, a corroded, or a loose connector terminal(s). Terminals must
have a slight drag when disassembled/assembled. If they slide apart/together without resistance, they will not
provide a good connection.
If the problem is at a stud, a bolt, or a sheet metal screw, check for corrosion, paint, or loose connections. Paint can
be a very good insulator.
When assembling the earth wire eyelets on the earth points, place an external type star washer below the wire
eyelet(s). If the system is marginal, you can also place a star washer between the nut or the sheet-metal screw at
the top wire eyelet. Tighten the fastener to the specification. Make sure the star washer makes contact with the
metal surface.
All the fasteners should be tightened so that the fastener head presses the earth wire eyelet or star washer to the
mounting surface and stops. Repair any stripped earth fasteners.
IMPORTANT:
Do not over-tighten the sheet-metal screws. Over-tightening can enlarge the hole and create a bad earth. If the
sheet-metal is enlarged, the screw will continue to turn. Drill a new correctly sized hole for the screw if an overtight
condition exists.