SECTION 6C3-2B - SYMPTOMS - GEN III V8 ENGINE
IMPORTANT:
Before performing any Service Operation or other procedure described in this Section, refer to Section 00
CAUTIONS AND NOTES in this VX Service Information for correct workshop practices with regards to
safety and/or property damage.
GENERAL DES CRIPTION
When no diagnostic trouble codes have been set and the Tech 2 scan tool data values are within 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 symptom.
Then, intermittent conditions are discussed. These preliminary pages 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.
Many of the s ymptom diagnostic s s tar t with a very important proc edur e, a visual/physical inspection. Always look for
the obvious first. 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, transmission , PCM, and PIM connectors. Are there any
disconnected wires or incorrectly installed components?
Finally, are there obvious signs that someone may have perform ed incorrect r epairs? These c hecks tak e 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 referred to in the VX Series Service
Information.
PCM / PIM
Since the PCM and PIM can have a failure which may affect only one circuit, following the Diagnostic Procedures, in
the VX Series Service Information, will determine which circuit has a problem and where it is.
If a diagnostic T able indicates that the PCM , PIM and/ or connection is the cause of a problem and the PCM
or PIM has been replaced, but does not correct the problem, one of the following may be the reason:
• There is a problem with the PCM or PIM terminal connections. The diagnostic Table will say "PCM or PIM
connections or PCM/PIM." The terminals may have to be removed from the connector in order to check them
properly.
• The PCM or PIM is not c or rec t f or the applic ation. T he inc or rec t PCM or PIM may cause a malfunction and may
or may not set a code.
• The problem is intermittent. This means that the problem is not present at the time the system is being
checked. In this case, refer to the SYMPTOMS Tables and make a careful physical inspection of all
components of the system involved.
• Shorted solenoid, relay coil, or harness. Solenoids and relays are turned ON and OFF by the PCM, using
internal electronic switches called "Drivers." Each "driver" is part of a group of four (called "Quad drivers").
Failure of one driver may cause other driver s in the set to m alfunction. Solenoid and relay coil resistance m ust
measure more than 20 ohms, in most cases. Less resistance may cause early failure of the PCM "driver."
Before replacing a PCM or PIM, be sure to check the coil resistance of all solenoids and relays controlled by the
PCM or PIM. See PCM and PIM wiring diagram for the solenoid(s) and relay(s) and the coil terminal
identification.
• The replacement PCM or PIM may be faulty. After the PCM or PIM is replaced, the system should be
rechecked for proper operation. If the diagnostic Table again indicates the PCM or PIM is the problem,
substitute a known good PCM or PIM. Although this is an extremely rare condition, it could occur.
ENGINE EARTH LOCATIONS
Figure 6C3-2B-1 Engine Powertrain Wiring Harness to Engine Assembly Earth Location.
1. Knock Sensors Jumper Harness Connector
2. PCM Earth Location Left Rear Head
3. PCM Earth Location Right Front Head
4. PCM Wiring Harness to A/C Compressor
SYMPTOMS
IMPORTANT PRELIMINARY CHECKS BEFORE STA RTING
Perform the Powertrain OBD Sy stem Check before using the System Tables, and verify all of the following are true:
• The PCM/PIM and CPL (Check Powertrain Lamp) are operating correctly.
• There are no PCM or PIM DTC(s) stored.
• Ensure that the engine coolant temperature is not above 130°C (266°F). This condition causes the PCM to
operate in Engine Coolant O ver T e mperature- Fuel Dis abled Mode. While in Engine Coolant O ver T e mperature-
Fuel Disabled Mode, the PCM turns the f uel O FF to f our c ylinders at a tim e in order to keep engine temperature
from reaching damaging levels. The system perceives Engine coolant Over Temperature as a lack of power,
mis s , or r ough idle. If the vehic le is oper ating in Engine Coolant Over Temper ature- F uel Disabled Mode, refer to
Section 6B3 ENGINE COOLING – GEN III V8 ENGINE, in VX Service Information for diagnosis.
• The Tech 2 scan tool data is within the normal operating range, refer to
Section 6C3-2 DIAGNOSIS – GEN III V8 ENGINE, in this VX Series Service Information.
• Verify the driver com plaint, and locate the correct symptom in the table of contents. Check the item s indicated
under that symptom.
INSPECTION
Several of the symptom procedures require a careful visual and physical inspection. This step is extremely
important-it can lead to correcting a problem without further checks and can save valuable time.
This check includes:
• The PCM/PIM earths for being clean, tight, and in their proper location.
• Vacuum hos es for splits , k ink s, and pr oper connections , as s hown on the Vehicle Emis sion Control Inf orm ation
label. Check thoroughly for any type of leak or restriction.
• The Mas s Air Flow (MAF) s ensor installation. T he arrows on the plastic portion of the sensor must point toward
the engine.
• The air intake ducts for being collapsed, split or for having damaged areas.
• Air leaks at throttle body mounting area, Mass Air Flow (MAF) sensor, and the intake manifold sealing surfaces.
• The ignition wires for cracking, hardness, proper routing and carbon tracking.
• The engine harness wiring and terminals for proper connections, pinches or cuts.
INTERMITTENTS
IMPORTANT:
Check for improper installation of electrical components if an intermittent condition exists. Inspect for aftermarket
theft deterr ent devices, lights and cellular phones . Ensure that no afterm arket equipm ent is connected to the Class
II circuit. If you c an not locate an interm ittent condition, a cellular phone signal c omm unication m ay be the caus e of
the condition.
IMPORTANT:
The problem may or may not turn ON the Check Powertrain Lamp (CPL) or store a DTC. DO NOT use the
Diagnostic Trouble Code (DTC) tables for intermittent problems. The fault must be present in order to locate the
problem.
Faulty electrical connections or wiring cause most intermittent problems. Perform a careful inspection for the
following conditions:
• Poor mating of the connector halves or a terminal not fully seated in the connector body (backed out).
• An improperly formed or damaged terminal.
• Reform or replace connector terminals in the problem circuit in order to insure proper contact tension.
• Poor terminal to wire connection requires removing the terminal from the connector body in order to check.
• Road test the vehic le with a Digital Multim eter ( DMM) J 39200 c onnected to the s uspected c ircuit. An abnorm al
voltage when the malfunction occurs is a good indication that there is a malfunction in the circuit being
monitored.
Use a scan tool in order to help detect inter mittent conditions. T he scan tool has sever al features that you can use
to locate an intermittent condition. Use the following features to find intermittent faults:
• You can trigger the Snaps hot f eatur e in order to captur e and s tore engine par ameters within the scan tool when
the malfunction occurs. You can then review this stored information in order to see what caused the
malfunction.
• Using the Scan Tool’s Freeze Frame/Fa ilure Records can als o aid in locating an intermittent c ondition. Review
and capture the information in the Freeze Frame/Failure Records associated with the intermittent DTC being
diagnosed. Drive the vehicle in the conditions that were present when the DTC was originally set.
IMPORTANT:
If the interm ittent condition exists as a start and then stall condition, check f or DTC(s) relating to the theft deterrent
system. Check for improper installation of electrical options such as lights, cellular phones etc.
Any of the following may cause an intermittent Check Powertrain Lamp (CPL) with no stored DTC:
• The ignition coils shorted to a earth, arcing at the ignition wires or the spark plugs.
• The PCM/PIM earths, refer to Section 12P WIRING DIAGRAMS, in VX Service Information.
• The Ignition Control ( IC) wires f or being routed too c lose to the sec ondary ignition wires , coils , or the generator.
Ensure that all of the circuits from the PCM to the ignition coils have good connections.
• An open diode across the A/C compressor clutch and the other open diodes, refer to
Section 12P WIRING DIAGRAMS, in VX Service Information.
Use the following tables when diagnosing a symptom complaint:
• Hard Start
• Surges/Chuggles
• Lack of Power, Sluggishness, or Sponginess
• Detonation/Spark Knock
• Hesitation, Sag, Stumble
• Cuts Out, Misses
• Poor Fuel Economy
• Rough, Unstable, or Incorrect Idle, Stalling
• Dieseling, Run-On
• Backfire
HARD START
Checks Actions
Definition: Engine cranks OK, but does not start for a long time. Does eventually run, may start but stalls immediately.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING in the VX Series Service Information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information.
• Refer to Service Bulletins for relevant information.
Sensor/System • Check the Engine Coolant Temperature (ECT) Sensor for an incorrect value.
Compare the Engine Coolant Temperature against the Intake Air Temperature
(IAT) on a cold engine. The ECT and IAT Sensor values should be within ± 3°C
(5°F) of each other. If the ECT Sensor is out of range with the IAT sensor,
check the resistance of the ECT sensor. Refer to Temperature vs Resistance
for resistance specifications. Replace the ECT Sensor if the resistance is not
within the specification. If the sensor is within the specification, repair ECT
signal circuit for high resistance.
• Check the Mass Air Flow sensor installation. A MAF sensor that is incorrectly
installed may cause hard starting. The embossed arrows on the MAF sensor
indicate the direction of the intake air flow. The arrow must point toward the
engine. Install the MAF in the proper direction. Refer to MAF Sensor
Replacement in Section 6C3-3 SERVICE OPERATIONS – in VX Service
Information.
Fuel System • Check the fuel pump relay operation. The fuel pump should turn ON for 2
seconds when you turn on the ignition. Refer to Fuel Pump Relay Circuit
Diagnosis in Section 6C3-2A DIAGNOSTIC TABLES – in VX Service
Information .
• A faulty in-take fuel pump check valve slows the fuel in the lines to drain back
to the tank after the engine stops. To check for this condition, refer to Fuel
System Diagnosis in Section 6C3-2A DIAGNOSTIC TABLES – in VX Service
Information .
• Check both injector fuses for being open. An open injector fuse causes four
injectors and four ignition coils not to operate. Replace the fuse. Inspect the
injector circuit and the ignition coil circuits for an intermittent short to earth.
• Check for a low fuel pressure condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in Section
6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a contaminated fuel condition.
Checks Actions
Ignition System • Check both injector fuses for being open. An open injector fuse causes four
injectors and four ignition coils not to operate. Replace the fuse. Inspect the
injector circuit and the ignition coil circuits for an intermittent short to earth.
• Check for proper ignition voltage output with spark tester J 26792. Refer to
Section 6D3-3 IGNITION SYSTEM – GEN III V8 ENGINE, in VX Service
Information .
• Remove the spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Incorrect gap
- Burned electrodes
- Heavy deposits
• Determine the causes of the fouling before replacing the spark plugs, if the
spark plugs are fuel or oil fouled.
• Check for bare or shorted ignition wires.
• Check for loose ignition coil earths.
• Check the spark plugs for proper heat range.
Refer to Section 6D3-3 IGNITION SYSTEM – GEN III V8 ENGINE in VX Service
Information.
Engine Mechanical • Excessive oil in combustion chamber - leaking valve seals. Refer to Section
6A3 ENGINE MECHANICAL– GEN III V8 ENGINE, in VX Service Information .
• Low cylinder compression. Refer to Section 6A3 ENGINE MECHANICAL–
GEN III V8 ENGINE, in VX Service Information.
• Inspect combustion chambers for excessive carbon build-up. Clean the
chambers using a de-carboning agent. Follow the instructions of the product.
• Check for incorrect basic engine parts. Inspect the following: Cylinders,
camshaft, pistons, etc.
Refer to Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE in VX Service
Information.
SURGES/CHUGGLES
Checks Actions
Definition: Engine power variation under steady throttle or cruise. Vehicle speeds up and slows down with no change in the
accelerator pedal position.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING in the VX Series Service Information.
• Refer to Service Bulletins for relevant information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information .
• Be sure the driver understands the operation of the transmission torque
converter clutch and A/C compressor operation as explained in the Owner’s
Handbook. Inform the driver on how the TCC and the A/C clutch operates.
Sensor/System • Check the Heated Oxygen Sensor (HO2S). The Heated Oxygen Sensors
(HO2S) should respond quickly to different throttle positions. If they do not,
check the HO2S for silicon or other contaminates from fuel or the use of
improper RTV sealant. The sensors 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 delivery to the engine causing a severe
driveability problem.
• Check the MAF sensor connections.
Fuel System • Check for a low fuel pressure condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in Section
6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a contaminated fuel condition.
• Check that each injector harness is connected to the correct injector/cylinder
according to the firing order (1-8-7-2-6-5-4-3). Relocate injector harnesses as
necessary.
• Check the items that cause an engine to run rich (long term fuel trim near
13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0152 HO2S Circuit High Voltage Bank 2 Right
Sensor .
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean condition, refer to DTC P0131 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0151 HO2S Circuit High Voltage Bank 2 Right
Sensor.
Checks Actions
Ignition System • Wet down the secondary ignition system with water from a spray bottle.
Wetting down the secondary ignition system may help locate damaged or
deteriorated components. Look/listen for arcing or misfiring as you apply the
water.
• Check for proper ignition voltage output with spark tester J 26792.
• Remove the spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Incorrect gap
- Burned electrodes
- Heavy deposits
• An incorrect spark plug gap will cause a driveability problem. Set the spark
plug gaps using a wire gauge gap tool (J 41319). Refer to Section 6D3-3
IGNITION SYSTEM – GEN III V8 ENGINE, in VX Service Information .
• If spark plugs are fouled, determine the cause of the fouling before replacing
them.
• For fuel fouling, refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC
P0175 Fuel Trim System Rich Bank 2 in Section 6C3-2A DIAGNOSTIC
TABLES – in VX Service Information, for diagnosis of the rich condition
• For oil fouling refer to Section 6A3 ENGINE MECHANICAL – GEN III V8
ENGINE, in VX Service Information, for diagnosis of the oil fouling condition.
• Check for loose ignition coil earths.
• Check the spark plugs for proper heat range. Refer to Section 6D3-3 IGNITION
SYSTEM – GEN III V8 ENGINE, in VX Service Information.
Engine Mechanical Ensure that the engine coolant temperature is not above 130°C (266°F). This
condition causes the PCM to operate in Engine Coolant Over Temperature-Fuel
Disabled Mode. While in Engine Coolant Over Temperature-Fuel Disabled Mode,
the PCM turns fuel OFF to four cylinders at a time to keep engine temperatures
from reaching damaging levels. The system perceives Engine Coolant Over
Temperature-Fuel Disabled Mode as a lack of power, miss, or rough idle. If the
vehicle operates in Engine Coolant Over Temperature-Fuel Disabled Mode, refer to
Section 6B3 ENGINE COOLING – GEN III V8 ENGINE, in VX Service Information.
Additional Checks • Inspect vacuum hoses for splits, kinks, proper connections and routing.
• Check the Torque Converter Clutch (TCC) operation. A TCC applying too soon
can cause the engine to detonate. Refer to Section 7C2 AUTOMATIC
TRANSMISSION – ELECTRICAL DIAGNOSIS, in VX Service Information.
LACK OF POWER, SLUGGISHNESS, OR SPONGINESS
Checks Actions
Definition: Engine delivers less than normal power. Little or no increase in speed when the accelerator pedal is partially
depressed.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING in the VX Series Service Information.
• Refer to Service Bulletins for relevant information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
• Remove the air filter element and check for dirt or for being restricted. Refer to
Air Cleaner Element Replacement in Section 6C3-3 SERVICE OPERATIONS
– in VX Service Information, and replace as necessary.
Fuel System • Check both injector fuses for being open. An open injector fuse causes four
injectors and four ignition coils not to operate. Replace the fuse. Inspect the
ignition coil circuits and the injector circuits for an intermittent short to earth.
• Check for a low fuel pressure condition. Refer to Section 6C3-2A
DIAGNOSTIC TABLES – GEN III V8 ENGINE, in the VX Series Service
Information.
• Check for a restricted fuel filter. Refer to Section 6C3-2A DIAGNOSTIC
TABLES – GEN III V8 ENGINE, in the VX Series Service Information.
• Check for a contaminated fuel condition.
• Check the items that cause an engine to run rich (long term fuel trim near -
13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0152 HO2S Circuit High Voltage Bank 2 Right
Sensor
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean condition, refer to DTC P0131 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0151 HO2S Circuit High Voltage Bank 2 Right
Sensor.
Sensor/System • Use the Tech 2 scan tool in order to monitor the knock sensor system for
excessive spark retard activity. Refer to Section 6C3-2A DIAGNOSTIC
TABLES in the VX Series Service Information.
Ignition System • Check both injector fuses for being open. An open injector fuses causes four
injectors and four ignition coils not to operate. Replace the fuse. Inspect the
ignition coil circuits and the injector circuits for an intermittent short to earth.
• Wet down the secondary ignition system with water from a spray bottle.
Wetting down the secondary ignition system may help locate damaged or
deteriorated components. Look/listen for arcing or misfiring as you apply the
water.
• Check for correct ignition voltage output with spark tester J 26792. Refer to
Electronic Ignition System Diagnosis Section 6C3-2C FUNCTIONAL CHECKS
– GEN III V8 ENGINE in the VX Series Service Information.
• Remove the spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Incorrect gap
- Burned electrodes
- Heavy deposits
• An incorrect spark plug gap will cause a driveability problem. Set the spark
plug gaps using a wire gauge gap tool (J 41319). Refer to Section 6D3-3
IGNITION SYSTEM – GEN III V8 ENGINE, in VX Service Information .
• If spark plugs are fouled, determine the cause of the fouling before replacing
them.
• For fuel fouling, refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC
P0175 Fuel Trim System Rich Bank 2 in Section 6C3-2A DIAGNOSTIC
TABLES – in VX Service Information, in the VX Series Service Information, for
diagnosis of the rich condition
• For oil fouling refer to Section 6A3 ENGINE MECHANICAL – GEN III V8
ENGINE, in VX Service Information, for diagnosis of the oil fouling condition.
• Check for loose ignition coil earths.
• Check the spark plugs for proper heat range. Refer to Section 6D3-3 IGNITION
SYSTEM – GEN III V8 ENGINE, in VX Service Information.
Checks Actions
Engine Mechanical • Ensure that the engine coolant temperature is not above 130°C (266°F). This
condition causes the PCM to operate in Engine Coolant Over Temperature-
Fuel Disabled Mode. While in Engine Coolant Over Temperature-Fuel
Disabled Mode, the PCM turns fuel OFF to four cylinders at a time to keep
engine temperatures from reaching damaging levels. The system perceives
Engine Coolant Over Temperature-Fuel Disabled Mode as a lack of power,
miss, or rough idle. If the vehicle operates in Engine Coolant Over
Temperature - Fuel Disabled Mode, refer to Section 6B3 ENGINE COOLING –
GEN III V8 ENGINE, in VX Service Information for diagnosis.
• Excessive oil in combustion chamber - leaking valve seals. Refer to Section
6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX Service Information .
• Low cylinder compression. Refer to Section 6A3 ENGINE MECHANICAL –
GEN III V8 ENGINE, in VX Service Information for diagnosis.
• For incorrect basic engine parts. Inspect the following:
- Camshaft
- Cylinder heads
- Pistons, etc.
Refer to Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX
Service Information for diagnosis.
Additional Checks • Check the exhaust system for possible restrictions. Check for the following:
- Inspect the exhaust system for damaged or collapsed pipes.
- Inspect the exhaust manifold for a collapsed inner wall.
- Inspect the muffler for heat distress or possible internal failure.
- Inspect for possible restricted catalytic converters by comparing exhaust
system back pressure on each side of the engine.
• Check Torque Converter Clutch (TCC) for proper operation. Refer to Section
7C2 AUTOMATIC TRANSMISSION – ELECTRICAL DIAGNOSIS, in VX
Service Information for diagnosis.
DETONATION/SPARK KNOCK
Checks Actions
Definition: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change
with throttle opening.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING in the VX Series Service Information.
• Refer to Service Bulletins for relevant information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information .
• If the Tech 2 scan tool readings are normal (refer to the supporting text of the
Powertrain On-Board Diagnostic (OBD) System Check) and there are no
engine mechanical faults, fill the fuel tank with a premium petrol that has a
minimum octane reading of 92 and re-evaluate the vehicle’s performance.
Fuel System • Check for a low fuel pressure condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis.
• Check for a contaminated fuel condition.
• Check the items that cause an engine to run rich (long term fuel trim near -
13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0152 HO2S Circuit High Voltage Bank 2 Right
Sensor.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean condition, refer to DTC P0131 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0151 HO2S Circuit High Voltage Bank 2 Right
Sensor.
Ignition System Check the spark plugs for proper heat range. Refer to Section 6D3-3 IGNITION
SYSTEM – GEN III V8 ENGINE, in VX Service Information.
Engine Mechanical Check for the following engine mechanical problems:
• Excessive oil in combustion chamber-leaking valve seals. Refer to Section 6A3
ENGINE MECHANICAL – GEN III V8 ENGINE, in VX Service Information .
• Low cylinder compression. Refer to Section 6A3 ENGINE MECHANICAL –
GEN III V8 ENGINE, in VX Service Information.
• Inspect combustion chambers for excessive carbon build-up. Clean the
chambers using a de-carboning agent. Follow the instructions of the product.
• For incorrect basic engine parts. Inspect the following:
- Cylinders
- Camshaft
- Pistons, etc.
• Refer to Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX
Service Information.
Additional Checks • Check the Park/Neutral Position (PNP) switch operation. Refer to Section 7C2
AUTOMATIC TRANSMISSION – ELECTRICAL DIAGNOSIS, in VX Service
Information for diagnosis.
• Check the TCC operation. The TCC applying too soon can cause the engine to
spark knock. Refer to Section 7C2 AUTOMATIC TRANSMISSION –
ELECTRICAL DIAGNOSIS, in VX Service Information for diagnosis.
HESITATION, SAG, STUMBLE
Checks Actions
Definition: Momentary lack of response as the accelerator is depressed. Can occur at any vehicle speed. Usually more
pronounced when first trying to make the vehicle move from a standing start. May cause the engine to stall if severe enough.
Preliminary • Refer to Symptoms, IMPORTANT Preliminary Checks Before Starting.
• Search for Service Bulletins.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information.
Sensor/System Check the MAP sensor operation. Refer to Section 63-2A DIAGNOSTIC TABLES,
in the VX Series Service Information.
Fuel System • Check for a low fuel pressure condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES in VX Service Information, in the VX
Series Service Information.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in Section
6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a contaminated fuel condition.
• Check both injector fuses for being open. An open injector fuse causes four
injectors and four ignition coils not to operate. Replace the fuse. Inspect the
ignition coil circuits and the injector circuits for an intermittent short to earth.
• Perform the injector balance test. Refer to Fuel Injector Balance Test in
Section 6C3-2C FUNCTIONAL CHECKS – in VX Service Information for
procedure.
• Check the items that cause an engine to run rich (long term fuel trim near -
13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0152 HO2S Circuit High Voltage Bank 2 Right
Sensor.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean condition, refer to DTC P0131 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0151 HO2S Circuit High Voltage Bank 2 Right
Sensor.
Checks Actions
Ignition System • Wet down the secondary ignition system with water from a spray bottle.
Wetting down the secondary ignition system may help locate damaged or
deteriorated components. Look/listen for arcing or misfiring as you apply the
water.
• Check both injector fuses for being open. An open injector fuse causes four
injectors and four ignition coils not to operate. Replace the fuse. Inspect the
ignition coil circuits and the injector circuits for an intermittent short to earth
• Check for proper ignition voltage output with spark tester J 26792. Refer to
Electronic Ignition System Diagnosis in Section 6C3-2C FUNCTIONAL
CHECKS – in VX Service Information, for procedure.
• Remove the spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Incorrect gap
- Burned electrodes
- Heavy deposits
• An Incorrect spark plug gap will cause a driveablitiy problem. Set the spark
plug gap using a wire gauge gap tool (J 41319). Refer to Section 6D3-3
IGNITION SYSTEM – GEN III V8 ENGINE, in VX Service Information .
• If spark plugs are fouled, determine the cause of the fouling before replacing
them.
• For fuel fouling, refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC
P0175 Fuel Trim System Rich Bank 2 in Section 6C3-2A DIAGNOSTIC
TABLES – in VX Service Information, for diagnosis of the rich condition
• For oil fouling refer to Section 6A3 ENGINE MECHANICAL – GEN III V8
ENGINE , in VX Service Information for diagnosis of the oil fouling condition.
• Check for loose ignition coil earths.
• Check the spark plugs for proper heat range. Refer to Section 6D3-3 IGNITION
SYSTEM – GEN III V8 ENGINE, in VX Service Information.
Engine Cooling System Check the engine thermostat for proper operation and for proper heat range. Refer
to in Section 6B3 ENGINE COOLING – in VX Service Information.
Additional Checks Check the generator output voltage. Refer to in Section 6D3-1 CHARGING
SYSTEM – in VX Service Information. Repair the charging system if the generator
output voltage is less than 9 volts or more than 16 volts.
CUTS OUT, MISSES
Checks Actions
Definition: Steady pulsation or jerking that follows engine speed, usually more pronounced as an engine load increases. This
condition is not normally felt above 1500 RPM or 48 km/h. The exhaust has a steady spitting sound at idle or low speed.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING in the VX Series Service Information.
• Refer to Service Bulletins for relevant information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information .
• Remove the air filter element and check for dirt or for being restricted. Refer to
Air Cleaner Element Replacement in Section 6C3-3 SERVICE OPERATIONS
– in VX Service Information, and replace as necessary.
Fuel System • Perform the injector balance test. Refer to Fuel Injector Balance Test for
procedure.
• Check for a low fuel pressure condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in Section
6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a contaminated fuel condition.
• Check the items that cause an engine to run rich (long term fuel trim near -
13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0152 HO2S Circuit High Voltage Bank 2 Right
Sensor.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean condition, refer to DTC P0131 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0151 HO2S Circuit High Voltage Bank 2 Right
Sensor.
Sensor/System • Use a Tech 2 scan tool in order to monitor the knock sensor system for
excessive spark retard activity. Refer to Section 6C3-2A DIAGNOSTIC
TABLES, in the VX Series Service Information.
Ignition System • Wet down the secondary ignition system with water from a spray bottle.
Wetting down the secondary ignition system may help locate damaged or
deteriorated components. Look/listen for arcing or misfiring as you apply the
water.
• Check for proper ignition voltage output with spark tester J 26792. Refer to
Electronic Ignition System Diagnosis in Section 6C3-2C FUNCTIONAL
CHECKS – in VX Service Information.
• Remove the spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Incorrect gap
- Burned electrodes
- Heavy deposits
• An Incorrect spark plug gap will cause a driveablitiy problem. Set the spark
plug gap using a wire gauge gap tool (J 41319). Refer to Section 6D3-3
IGNITION SYSTEM – GEN III V8 ENGINE, in VX Service Information .
• If spark plugs are fouled, determine the cause of the fouling before replacing
them.
• For fuel fouling, refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC
P0175 Fuel Trim System Rich Bank 2 in Section 6C3-2A DIAGNOSTIC
TABLES – in VX Service Information, for diagnosis of the rich condition
• For oil fouling refer to Section 6A3 ENGINE MECHANICAL – GEN III V8
ENGINE, in VX Service Information, for diagnosis of the oil fouling condition.
• Refer to Electronic Ignition System Diagnosis in Section 6C3-2C
FUNCTIONAL CHECKS – in VX Service Inform ation.
• Inspect the Secondary ignition for the following:
- Ignition wires for cross firing
- Ignition wires arcing to earth
- Ignition wires for proper routing
• - Ignition coils for crack or carbon tracking
Checks Actions
Engine Mechanical • Check engine mechanical for the following:
- Check compression
- Sticking or leaking valves
- Worn camshaft lobes
- Valve timing
- Bent push rods
- Worn roc ker arms
- Broken valve springs
- Excessive oil in combustion chamber - leaking valve seals
- Low cylinder compression
• For incorrect basic engine parts. Inspect the following:
- Camshaft
- Cylinder heads
- Pistons, etc.
Refer to in Section 6A3 ENGINE MECHANICAL – in VX Service Information.
Additional Checks • Check the exhaust system for possible restrictions. Check for the following:
- Inspect the exhaust system for damaged or collapsed pipes.
- Inspect the exhaust manifold for a collapsed inner wall.
- Inspect the muffler for heat distress or possible internal failure.
- Inspect for possible restricted catalytic converters by comparing exhaust
system back pressure on each side of the engine. Check back pressure by
removing the Heated Oxygen Sensors.
• Electromagnetic Interference (EMI) on the reference circuit can cause an
engine miss condition. A sudden increase in engine RPM with no change of
throttle position indicates EMI may be present. Check routing of secondary
ignition wires, high voltage components (near ignition control circuits) if a
problem exists.
• Check the intake manifold and the exhaust manifold passages for casting
flash. Refer to in Section 6A3 ENGINE MECHANICAL – in VX Service
Information.
POOR FUEL ECONOMY
Checks Actions
Definition: Fuel economy, as measured by an actual road test, is noticeably lower than normal.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING in the VX Series Service Information.
• Refer to Service Bulletins for relevant information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information .
• Check the driver’s driving habits.
• Is the A/C ON or the demister mode ON all the time?
• Are the tyres at the correct pressure?
• Are excessively heavy loads being carried?
Fuel System • Remove the air filter element and check for dirt or for being restricted.
• Perform the injector balance test. Refer to Fuel Injector Balance Test in
Section 6C3-2 FUNCTIONAL CHECKS – in VX Service Information .
• Check for a low fuel pressure condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in Section
6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a contaminated fuel condition.
• Check that each injector harness is connected to the correct injector/cylinder
according to the firing order (1-8-7-2-6-5-4-3). Relocate injector harness as
necessary.
• Check for injectors that are shorted internally. Compare the injector
resistances. Injector resistance should be within one ohm of each other. Refer
to Fuel Injector Coil Test - ECT Between 10-35° C in Section 6C3-2
FUNCTIONAL CHECKS – in VX Service Information for procedure.
• Check for foreign material accumulation in the throttle bore, carbon build-up on
the throttle valve, or on the throttle shaft. Also, inspect for throttle body
tampering.
• Check the items that cause an engine to run rich (long term fuel trim near -
13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0152 HO2S Circuit High Voltage Bank 2 Right
Sensor.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean condition, refer to DTC P0131 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0151 HO2S Circuit High Voltage Bank 2 Right
Sensor.
Sensor/System • Check the air intake system and crankcase for air leaks.
• Check the PCV System for correct operation. Place a finger over the inlet hole
in the valve end several times. The valve should snap back. If not, replace the
valve.
• Check for proper calibration of speedometer. Using the Tech 2 scan tool,
command vehicle speed output. Speedometer should read same as Tech 2
output. If not, refer to Section 12C INSTRUMENTS, WIPERS/WASHERS &
HORN, in VX Service Information.
• Use the Tech 2 scan tool in order to monitor the knock sensor system for
excessive spark retard activity. Refer to Section 6C3-2A DIAGNOSTIC
TABLES, in the VX Series Service Information.
Checks Actions
Ignition System • Check for proper ignition voltage output with spark tester J 26792. Refer to
Electronic Ignition System Diagnosis in Section 6C3-2C FUNCTIONAL
CHECKS – in VX Service Information.
• Remove the spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Incorrect gap
- Burned electrodes
- Heavy deposits
• An incorrect spark plug gap will cause a driveablitiy problem. Set the spark
plug gap using a wire gauge gap tool (J 41319). Refer to Section 6D3-3
IGNITION SYSTEM – GEN III V8 ENGINE, in VX Service Information .
• If spark plugs are fouled, determine the cause of the fouling before replacing
them.
• For fuel fouling, refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC
P0175 Fuel Trim System Rich Bank 2 in Section 6C3-2A DIAGNOSTIC
TABLES – in VX Service Information for diagnosis of the rich condition
• For oil fouling, refer to Section 6A3 ENGINE MECHANICAL – GEN III V8
ENGINE, in VX Service Information, for diagnosis of the oil fouling condition.
• Inspect the Secondary ignition for the following:
- Ignition wires arcing to earth
- Ignition wires for proper routing
• Wetting down the secondary ignition system with water from a spray bottle
may help locate damaged or deteriorated components. Look and listen for
arcing or misfiring as you apply water.
• Check for loose ignition coil earths.
Engine Cooling System • Check the engine coolant level for being low. Refer to Section 6B3 ENGINE
COOLING – GEN III V8 ENGINE, in VX Service Information.
• Check the engine thermostat for proper operation and for the correct heat
range. Refer to Section 6B3 ENGINE COOLING – GEN III V8 ENGINE, in VX
Service Information.
Checks Actions
Engine Mechanical • Check engine mechanical for the following:
- Check compression
- Sticking or leaking valves
- Worn camshaft lobes
- Valve timing
- Bent push rods
- Worn roc ker arms
- Broken valve springs
- Excessive oil in combustion chamber - leaking valve seals
- Low cylinder compression
• For incorrect basic engine parts. Inspect the following:
- Cylinders
- Camshaft
- Pistons, etc.
Refer to Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX Service
Information.
Additional Checks • Check the vacuum hoses for splits, kinks, and proper connections.
• Check the TCC operation. The Tech 2 scan tool should indicate an RPM drop,
when the system commands the TCC ON. Refer to Section 7C2 AUTOMATIC
TRANSMISSION – ELECTRICAL DIAGNOSIS, in VX Service Information. .
Check the exhaust system for possible restrictions. Check for the following:
- Inspect the exhaust system for damaged or collapsed pipes.
- Inspect the exhaust manifold for a collapsed inner wall.
- Inspect the muffler for heat distress or possible internal failure.
- Inspect for possible restricted catalytic converters by comparing exhaust
system back pressure on each side of the engine. Check back pressure by
removing the heated oxygen sensors.
• Electromagnetic Interference (EMI) on the reference circuit can cause an
engine miss condition. A sudden increase in engine RPM with no change of
throttle position indicates EMI may be present. Check routing of secondary
ignition wires, high voltage components (near ignition control circuits) if a
problem exists.
• Check PNP s witch circ uit. Refer to Section 7C2 AUTOMATIC TRANSMISSION
– ELECTRICAL DIAGNOSIS, in VX Service Information.
• Check for faulty engine mounts. Refer to Section 6A3 ENGINE MECHANICAL
– GEN III V8 ENGINE, in VX Service Information for inspection of mounts.
• Check the intake and the exhaust manifold passages for casting flash. Refer to
Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX Service
Information.
ROUGH, UNSTABLE, OR INCORRECT IDLE , STALLING
Checks Actions
Definition: Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM.
Either condition may be severe enough to stall the engine.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING in the VX Series Service Information.
• Refer to Service Bulletins for relevant information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information.
• Remove and check the air filter element for dirt, or for being restricted. Refer to
Air Cleaner Element Replacement in Section 6C3-3 SERVICE OPERATIONS
– in VX Service Information. Replace as necessary.
Fuel System • Perform the injector balance test. Refer to Fuel Injector Balance Test in
Section 6C3-2C FUNCTIONAL CHECKS in VX Service Information for this
procedure.
• Check for a low fuel pressure condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in Section
6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a contaminated fuel condition.
• Check that each injector harness is connected to the correct injector/cylinder
according to the firing order (1-8-7-2-6-5-4-3). Relocate injector harness as
necessary.
• Check the items that cause an engine to run rich (long term fuel trim near -
13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0152 HO2S Circuit High Voltage Bank 2 Right
Sensor.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean condition, refer to DTC P0131 HO2S Circuit High Voltage
Bank 1 Left Sensor and DTC P0151 HO2S Circuit High Voltage Bank 2 Right
Sensor.
Sensor/System • Check the PCV System for correct operation. Place a finger over inlet hole of
the valve end several times. valve should snap back. If not, replace the valve.
• Use the Tech 2 scan tool in order to monitor knock sensor system for
excessive spark retard activity. Refer to Section 6C3-2A DIAGNOSTIC
TABLES, in the VX Series Service Information.
Ignition System • Check for proper ignition voltage output with spark tester J 26792. Refer to
Electronic Ignition System Diagnosis in Section 6C3-2C FUNCTIONAL
CHECKS – in VX Service Information.
• Remove the spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Incorrect gap
- Burned electrodes
- Heavy deposits
• An Incorrect spark plug gap will cause a driveablitiy problem. Set the spark
plug gap using a wire gauge gap tool (J 41319). Refer to Section 6D3-3
IGNITION SYSTEM – GEN III V8 ENGINE, in VX Service Information .
• If spark plugs are fouled, determine the cause of the fouling before replacing
them.
• For fuel fouling, refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC
P0175 Fuel Trim System Rich Bank 2 in Section 6C3-2A DIAGNOSTIC
TABLES – in VX Service Information, for diagnosis of the rich condition
• For oil fouling, refer to Section 6A3 ENGINE MECHANICAL – GEN III V8
ENGINE, in VX Service Information, for diagnosis of the oil fouling condition.
• Inspect the Secondary ignition for the following:
- Ignition wires arcing to earth
- Ignition wires for proper routing
• Wetting down the secondary ignition system with water from a spray bottle
may help locate damaged or deteriorated components. Look and listen for
arcing or misfiring as you apply water.
• Check for loose ignition coil earths.
Techline
Checks Actions
Engine Mechanical • Check engine mechanical for the following:
- Check compression
- Sticking or leaking valves
- Worn camshaft lobes
- Valve timing
- Bent push rods
- Worn roc ker arms
- Broken valve springs
- Excessive oil in combustion chamber - leaking valve seals
- Low cylinder compression
• For incorrect basic engine parts. Inspect the following:
- Cylinder
- Camshaft
- Pistons, etc.
Refer to Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX Service
Information.
Additional Checks • Check the exhaust system for possible restrictions. Check for the following:
- Inspect the exhaust system for damaged or collapsed pipes.
- Inspect the exhaust manifold for a collapsed inner wall.
- Inspect the muffler for heat distress or possible internal failure.
- Inspect for possible restricted catalytic converters by comparing exhaust
system back pressure on each side of the engine. Check back pressure by
removing the heated oxygen sensors.
• Electromagnetic Interference (EMI) on the reference circuit can cause an
engine miss condition. A sudden increase in engine RPM with no change of
throttle position indicates EMI may be present. Check routing of secondary
ignition wires, high voltage components (near ignition control circuits) if a
problem exists.
• Check PNP switch circuit.
• Check for faulty engine mounts. Refer to Section 6A3 ENGINE MECHANICAL
– GEN III V8 ENGINE, in VX Service Information for inspection of the mounts.
• Check the intake and the exhaust manifold passages for casting flash. Refer to
Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX Service
Information.
DIESELING, RUN-ON
Checks Actions
Definition: Engine continues to run after key is turned OFF, but runs very rough. If the engine runs normally, check the
ignition switch and the ignition switch adjustment.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING in the VX Series Service Information.
• Refer to Service Bulletins for relevant information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information .
• Pre-ignition due to build up of carbon in the combustion chamber.
Fuel System Inspect the injectors for leaking condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES – in VX Service Information, for this
procedure.
BACKFIRE
Checks Actions
Definition: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Preliminary • Refer to SYMPTOMS, IMPORTANT PRELIMINARY CHECKS BEFORE
STARTING, in the VX Series Service Information.
• Refer to Service Bulletins for relevant information.
• Check the PCM/PIM earths for being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS, in VX Service Information.
Fuel System • Check for a low fuel pressure condition. Refer to Fuel System Diagnosis in
Section 6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in Section
6C3-2A DIAGNOSTIC TABLES – in VX Service Information.
• Check for a contaminated fuel condition.
• Check that each injector harness is connected to the correct injector/cylinder
according to the firing order (1-8-7-2-6-5-4-3). Relocate injector harness as
necessary.
Sensor/System • Check the air intake system and crankcase for air leaks.
• Check the PCV System for correct operation. Place a finger over the inlet hole
in the valve end several times. The valve should snap back. If not, replace the
valve.
• Check for proper calibration of speedometer. Using Tech 2 scan tool,
command vehicle speed output, speedometer should read same as Tech 2
output. If not, refer to Section 12C INSTRUMENTS, WIPERS/WASHERS &
HORN, in VX Service Information.
• Use the Tech 2 scan tool in order to monitor the knock sensor system for
excessive spark retard activity. Refer to Section 6C3-2A DIAGNOSTIC
TABLES, in the VX Series Service Information.
Ignition System • Check for proper ignition voltage output with spark tester J 26792. Refer to
Electronic Ignition System Diagnosis in Section 6C3-2C FUNCTIONAL
CHECKS – in VX Service Information.
• Check for an intermittent ignition system malfunction in the following circuits:
- Intermittent ignition control circuit.
- Use the scan tool’s Snapshot feature in order to help locate an intermittent
ignition failure.
• Remove the spark plugs and check for the following:
- Wet plugs
- Cracks
- Wear
- Incorrect gap
- Burned electrodes
- Heavy deposits
• An Incorrect spark plug gap will cause a driveablitiy problem. Set the spark
plug gap using a wire gauge gap tool (J 41319). Refer to Section 6D3-3
IGNITION SYSTEM – GEN III V8 ENGINE, in VX Service Information .
• If spark plugs are fouled, determine the cause of the fouling before replacing
them.
• For fuel fouling, refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC
P0175 Fuel Trim System Rich Bank 2 in Section 6C3-2A DIAGNOSTIC
TABLES – in VX Service Information, for diagnosis of the rich condition
• For oil fouling refer to Section 6A3 ENGINE MECHANICAL – GEN III V8
ENGINE, in VX Service Information, for diagnosis of the oil fouling condition.
• Inspect the Secondary ignition for the following:
- Ignition wires for cross firing
- Ignition wires arcing to earth
- Ignition coils arcing routing
• Wetting down the secondary ignition system with water from a spray bottle
may help locate damaged or deteriorated components. Look and listen for
arcing or misfiring as you apply water.
• Check for loose ignition coil earths.
Checks Actions
Engine Cooling System • Check the engine coolant level for being low. Refer to Section 6B3 ENGINE
COOLING – GEN III V8 ENGINE, in VX Service Information.
• Check the engine thermostat for proper operation and for the correct heat
range. Refer to Section 6B3 ENGINE COOLING – GEN III V8 ENGINE, in VX
Service Information.
Engine Mechanical • Check engine mechanical for the following:
- Check compression
- Sticking or leaking valves
- Worn camshaft lobes
- Valve timing
- Bent push rods
- Worn roc ker arms
- Broken valve springs
- Excessive oil in combustion chamber - leaking valve seals
- Low cylinder compression
• Check for incorrect basic engine parts. Inspect the following:
- Cylinder
- Camshaft
- Pistons, etc.
• Refer to Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX
Service Information.
Additional Checks • Check the vacuum hoses for splits, kinks, proper connections and routing.
• Check the TCC operation. The scan tool should indicate an RPM drop, when
the system commands the TCC ON. Refer to Section 7C2 AUTOMATIC
TRANSMISSION – ELECTRICAL DIAGNOSIS, in VX Service Information.
• Check the exhaust system for possible restrictions. Check for the following:
- Inspect the exhaust system for damaged or collapsed pipes.
- Inspect the exhaust manifold for a collapsed inner wall.
- Inspect the muffler for heat distress or possible internal failure.
- Inspect for possible restricted catalytic converters by comparing exhaust
system back pressure on each side of the engine. Check back pressure by
removing the Heated Oxygen Sensors. Refer to Restricted Exhaust System
Checks and Engine Exhaust.
• Electromagnetic Interference (EMI) on the reference circuit can cause an
engine miss condition. A sudden increase in engine RPM with no change of
throttle position indicates EMI may be present. Check routing of secondary
ignition wires, high voltage components (near ignition control circuits) if a
problem exists.
• Check PNP s witch circ uit. Refer to Section 7C2 AUTOMATIC TRANSMISSION
– ELECTRICAL DIAGNOSIS, in VX Service Information for diagnosis.
• Check for faulty engine mounts. Refer to Section 6A3 ENGINE MECHANICAL
– GEN III V8 ENGINE, in VX Service Information for inspection of the mounts.
• Check the intake and the exhaust manifold passages for casting flash. Refer to
Section 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, in VX Service
Information.
RESTRICTED EXHAUST SYSTEM CHECK
Step Action Value(s) Yes No
1 Did you perform the Powertrain On-Board Diagnostic
(OBD) System Check? Go to Step 2 Go to Powertrain
OBD System
Check
2 1. Carefully remove the HO2S for Bank 1 Left Sensor.
2. Install the Exhaust Back Pressure tester BT-8515 in
place of the Heated Oxygen Sensor.
3. Idle the engine at normal operating temperature.
4. Observe the exhaust system back pressure reading
on the gauge.
Does the reading exceed the specified value?
8.6 kPa
(1.25 psi)
Go to Step 5 Go to Step 3
3 1. The Exhaust Back pressure Gauge still installed.
2. Increase engine speed to 2000 RPM.
3. Observe the exhaust system back pressure reading
on the gauge.
Does the reading exceed the specified value?
20.7 kPa
(3 psi)
Go to Step 6 Go to Step 4
4 1. Ignition OFF.
2. Reinstall Bank 1 HO2S.
3. Carefully remove the HO2S for Bank 2 Right Sensor.
4. Install the Exhaust Back Pressure tester BT-8515 in
place of the Heated Oxygen Sensor.
5. Idle the engine at normal operating temperature.
6. Observe the exhaust system back pressure reading
on the gauge.
Does the reading exceed the specified value?
8.6 kPa
(1.25 psi)
Go to Step 6 Go to Step 5
5 1. The Exhaust Back pressure Gauge still installed.
2. Increase engine speed to 2000 RPM.
3. Observe the exhaust system back pressure reading
on the gauge.
Does the reading exceed the specified value?
20.7 kPa
(3 psi)
Go to Step 6 No Exhaust
Restrictions
found. If a
driveability
symptom exists,
refer to
SYMPTOMS
6 Repair the restriction in the exhaust system. Check
exhaust system for the following:
• Restricted Exhaust Manifolds
• Collapsed pipes
• Heat distress
• Internal muffler failure
• Damaged Catalytic Converter
Is the action complete?
System OK
TESTING EARTHS
Unusual displays in the instrument cluster, lamps
that are dim or flash unexpectedly, unexpected
readings - gremlins? Probably not; these are
classic symptoms of earth problems.
This section discusses the importance of good
earth circuits. It starts by explaining some basic
theories. Then, you are shown how to diagnose a
solid-state circuit earth condition and how, if there
is a problem, to correct it.
BASICS
For a circuit to operate properly, you need three
things - a good power supply to components, good
components, and good earths. Circuits are
complete systems; current must flow from
beginning to end as designed, not hindered by
unexpected resistance anywhere in the circuit.
Some tec hnic ians r ealis e that the power supply to a
circuit must be free of unwanted resistance, but
have difficulty visualising why an earth circuit must
also be f r ee of unwanted res istanc e. Curr ent f low is
through a complete circuit; it passes through and
out of a component like water flowing through a
tub. With a properly draining tub (no clogs), the
water can flow out as freely as it flowed in. Current
mus t enter and leave c om ponents f reely, if they are
to perform as designed.
3
RI
4
4289
2
1
Figure 6C3-2B-2
1. Voltage = Resistance X Current V = R X I
2. Resistance = Current Relationship With Fixed Voltage
3. Large Resistance, Small Current
4. Small Resistance, Large Current
Sensitive solid-state systems have their own earths;
high cur rent devices (lik e motor s) do not earth at the
same location. High current devices can cause
voltage spikes (sudden changes in voltage) when
turned ON or OFF. To prevent these spikes from
affecting sensitive solid-state circuits, the two
different types of systems use different earth
locations. The use of a dedicated wire to connect an
isolated earth junction block to the battery negative
terminal. This wire reduces the effect of spikes on
sensitive circuits at the earth junction block.
Solid-state circuits are particularly sensitive to poor
circuit c ontinuity becaus e in mos t cases they use low
current flow. This section on testing earths concerns
one solid-state device, the PCM. However, the
information included here applies to all solid-state
earth circuits.
Severe restrictions in the earth circuit can cause
resets and intermittent codes in solid-state systems.
The PCM operates devices (fuel injectors, idle air
control, etc.) and receives inputs from low voltage
sensors, manifold absolute pressure sensor,
crankshaft speed/position. These input and output
devices need good circuitry for correct operation.
Remember, that when maladjusted or imperfect
sensors cause values to shift there are usually
driveability problems. If there is excessive resistance
in the earth circ uit, the res ult 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 vehicle efficiency and performance and may
be noticed by the driver.
SENSOR CIRCUIT EARTH SENSITIVITY
- an example.
Looking at the Throttle Position (TP) Sensor circuit
will provide an example of how a little resistance in
the earth circuit can cause problems. The
accompanying figure shows a TP Sensor first with
a good earth circuit and then with a poor
connection in the earth circuit. Refer to this figure
as you proceed through the text that follows.
A Throttle Position Sensor consists of a resistor
and a wiper. One terminal of the resistor is
connected to a supply voltage and the other earth.
As the wiper moves along the resistor, the voltage
of the wiper terminal progressively changes. If the
wiper is near the supply voltage end of the resist or,
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 exam ple). (The ac tual closed and wide open
throttle voltage specifications m ay vary for diff erent
engines.) The sensor output should never be
greater than reference supply voltage or less then
.20 volts. (The PCM would set a diagnostic trouble
code if this occurs.)
The diagram to the right shows voltage drops
across various points in the circuit. In the example
with good circuit earth, the TP 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.
Now, look at the sens or with the bad signal caused
by resistance in the earth circuit. The throttle
positions stays the same but the sensor output
voltage changes. In this example the increased
resistanc e causes an additional voltage drop of 0.5
volts. The voltage drop from the wiper to found 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
Now you can s ee why good earths are needed and
how sensitive some circuits can be.
EARTH CIRCUITS
How do you know which wires are earth wires,
which connectors they go through, and whether
they are connected to an earth junction or the
body?
Section 12P WIRING DIAGRAMS in Section in VX
Service Information 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.
1
23
4
5
7
4290
11
10
9
8
6
23
10
12
Figure 6C3-2B-3
Voltage Drop Illustration
1. Sensor With Good Earth.
2. Fixed 5 Volts.
3. Throttle Position Sensor.
4. 0.5 Volts Sensor Output.
5. Wiper.
6. Sensor With Poor Earth.
7. 1.0 Volts Sensor Output.
8. Voltage Drop Caused By Resistance of Poor Earth is 0.5
Volts.
9. Total Voltage Drop Below Wiper is 1.0 Volts.
10. Voltage Drop of 0.5 Volts.
11. Voltage Drop of 4.0 Volts.
12. Voltage Drop of 4.5 Volts.
If you suspect sever al cir cuits ar e being af f ec ted by a
poor or a back-feed to earth, look at the circuits to
see how the systems m ight interact. If they have any
common earth wires, that is where you should start
your diagnosis.
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; that is, they have more than one wire
connecting to earth. The PCM has more than one
earth circuit wire. There are several reasons for
redundant earths.
The PCM has many low-current circuits, but the
current from all these circuits (when they are
active) adds up to a larger current. Higher current
loads are managed more easily with several regular
size wires, rather than with one large diameter wire.
Basic circuit theory shows that the effective
resistance of parallel resistors is less than any of
the individual resistors. This is true for even the
small resistances in wires. Parallel wires provide
the lowest resistance. Because of them, in many
solid-state systems a pr oblem with one of the earth
wires would not affect the circuit; the redundant
wires could handle the c ur rent load. F or other s olid-
state systems the loss of even one redundant ear th
may affect operation, but the remaining earth
wire(s) may allow the vehicle to be driven.
Here is one exam ple which can pr ove to be dif ficult
to diagnose:
Symptom: A vehicle has driveability symptoms.
W henever a Tech 2 scan tool is connected and
the vehicle 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 scan tool is plugged in, a good earth
path is provided for the PCM through the Data
Link Connec tor ( DLC). T he DLC uses a diff erent
earth than the PCM.
Always test for driveability symptoms before
hooking up a scan tool. If they disappear when the
scan tool is hooked up, 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
complete open in the circuit has the most severe
effect. Use the severity of the symptom(s) as an
indication of the extent of the resistance in the
earth circuit.
Figure 6C3-2B-4
Figure 6C3-2B-4
1 1 1 1
------ = -------- + ------ + ------- +
R TOTAL R 1 R 2 R 3
EXAMPLE: 2 PARALLEL CIRCUITS, ONE WITH
ONE OHM RESISTANCE AND
THE OTHER WITH TWO OHMS
RESISTANCE.
1 1 1
------ = -------- + ------
R TOTAL 11 2 2
1 2 1
------ = -------- + ------
R TOTAL 2 2
1 3
------ = --------
R TOTAL 2
2
R TOTAL = -------- Ω
3
WITH METER
NEGATIVE (BLACK)
PROBE AT THE
BATTERY NEGATIVE
TERMINAL, PLACE THE
METER POSITIVE (RED)
PROBE BETWEEN:
MAXIMUM ALLOWABLE
VOLTAGE
SENSOR AND PCM
0.060 (60 MILLIVOLTS)
PCM AND BATTERY
NEGATIVE TERMINAL
0.020 (20 MILLIVOLTS)
CHECKING EARTHS
Once you determine that the cause of the vehic le symptom (s) m ay be caused by a bad earth, it is tim e to check f or
poor earth with one more tool: a high-impedance voltmeter.
The best way to check for poor earth c onnections in low-curr ent solid-state c ircuits is to c heck the voltage dr op. To
do this you need a high-impedance voltmeter rated at a minimum of 10 megaohms (10,000,000 ohms) per volt.
Most quality digital multimeters meet or exceed this specification. Voltmeters with less impedance can affect the
circuit you are testing and also give an incorrect reading.
Start by checking the entire suspect earth circuit. With a voltmeter set on the 2 volt DC scale, connect the black
negative lead to the batter y negative term inal. ( If you are using an auto-ranging m eter, s et it to the DC volts setting.
Connect the red positive lead to the earth terminal of the component to be tes ted. W ith the circuit activated, c heck
the voltage drop in the circ uit. If the voltage reading is within specif ications, look f or a caus e 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 c irc uit. (Keep the negative lead c onnected to the batter y negative terminal.) Be sure
to check both sides of each in-line connector and both the eyelet and the stud or screw at earth points. Repeat this
process through the earth path until the voltmeter reading is within specifications. The high resistance causing the
earth problem is located between where you obtained a good reading and the last high reading.
When a c ircuit us es redundant earths be sure to c heck
all the earth circuits for excessive voltage drop.
SOLID-STATE CIRCUIT VOLTAGE DROP SPECIFICATIONS
There ar e two ac c eptable maximum voltage dr ops for solid- state c irc uits . If you are meas ur ing the voltage drop of a
circuit that will pass through a solid-s tate com ponent bef ore going to earth (suc h as the ECT sensor circuit between
the ECT sensor and the PCM), measured voltage cannot be higher than 0.060 volts (60 millivolts).
If you are measuring 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 measured
voltage is 0.020 volts (20 millivolts). If you measure a voltage above specifications, repair the earth circuit.
Checking the voltage drop in a solid-state sensor circuit - an example. Look again at a throttle position sensor
circuit. W ith the voltmeter negative lead connected to the negative battery terminal and the ignition in RUN, check
the voltages at various points between the ECT sensor pin "B" and pin "E16" of the PCM. A voltage reading of 0.060
volts or less with the meter positive lead at the ECT sensor pin "B" terminal indicates that the entire earth circuit
from the ECT sensor to the battery is continuous and suf ficiently low in r esistance. A voltage reading of 0.060 volts
at "the splice" or the PCM connector "E16" pin would also be within specifications.
When voltage measurements are made 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 voltage is not within specifications check the
diff erent connectors to find where the exces s voltage is. Be sure to c heck both s ides of in-line connector s and both
the eyelet and the stud at earth points.
Figure 6C3-2-6 Testing Voltage Drop Before the PCM
1. Throttle Position Sensor. 5. Red Lead.
2. Engine Coolant Temperature Sensor. 6. Black Lead.
3. PCM 7. Battery.
4. Sensor Return. 8. 0.60 Volts Maximum.
8
5
6
7
5
12
4
3
4291
5
Figure 6C3-2B-7 Testing Voltage Drop After the PCM
1. Earth. 5. Black Lead.
2. PCM. 6. Battery3
3. Oxygen Sensor 7. 0.020 Volts Maximum.
4. Red Lead
4
4
4
4
4
3
2
111
5
6
7
4292
G3PCM002PT
J2-57
J2-25
A
B
INTAKE AIR
TEMPERATURE SENSOR
SENSOR EARTH
IAT SENSO R SIGN AL
PCM
5V
BR (472 )
G/O (469)
YE23 YE123
M
I
C
R
O
EARTH CREDIBILITY CHE CK
CIRCUIT DESCRIPTION:
The earth credibility check can be either used at the beginning of all diagnostic pr ocedures or it can be used when
no diagnostic trouble codes are set, but a sy mptom still exists.
Test Description: Number(s) below refer to step number(s) on the diagnostic Table.
1. To properly test the voltage drop of the powertrain control module system earth a load must be present on
the circuit.
Using the scan tool:, select CANISTER PURGE. By turning "ON" the Purge solenoid, this will cause a
sufficient draw on the system for testing.
2. Check connectors in earth circuit to find where the excessive voltage is. Make sure to check both sides of
in-line connectors.
Diagnostic Aids:
Because the powertrain control module operates on such small current even a minor corrosion problem will cause
problems with the system. Make sure the earths are clean and tight. Remember a good earth is about 25% of the
total systems circuit. Normally you will check the wiring for: power, continuity, the load, but rarely check the earth.
Powertrain control module system earths are very important to proper operation.
Y E 123
P.C.M CONNE CTOR 2
(750)
(1228)
(1229)
(465)
(121)
(259)
G/B
BR
G/W
GY/BLU
R
B/R
(418)
BR
(59)
(832)
G
T
(831)
(417)
(472)
(976) (974)
(432)
(428)
(631)
BLU BR G/Y
BLU/W
LG
BR/W
W/B
LG W
(977)
Y
(971)
BLU/W W
B/R
(750)
(304)
(792)
(1223)
(1222)
(123)
(1227)
(469)
(331)
Y/B
LG
V/W
B/Y
G/O BR/W
(1687)
GY/B
(366)
LG/B
GY/R
(422)
V
(442)
(444)
(443)
(975)
(972)
(978)
(1224)
(973)
(959)
LG/W
LG/B
LBLU/B
GY
(773)
BR/Y
BLU
G
Y/B
LBLU
(958)
BR
(441)
LBLU
1
41
40
80
J2
RED
Y
(838)
AIR TEMP SENS OR
YE 23
B/R
(472)
G/O
(469)
STEP ACTION VALUE YES NO
1. Was the "On-Board Diagnostic" (OBD) System Check
performed? Go to Step 2. Go to OBD
System Check.
2. 1. Ignition "OFF"
2. Disconnect IAT sensor connector.
3. Using digital volt ohm meter set to DC voltage scale,
connect negative lead to negative battery cable at
battery and connect positive lead to the black wire at
the IAT sensor connector.
4. Ignition "ON"
5. Using a scan tool, select CANISTER PURGE.
6. Turn "ON'" Canister Purge with up/down arrow keys.
Is voltage measured less than value shown.
0.060 volts
(60 Millivolts) No problem
found, continue
with symptom
diagnosis.
Go to Step 3
3. 1. Remove and thoroughly clean the PCM earth
terminals and connection.
2. Reassemble the PCM Earth terminals.
Is action complete?
Verify Repair
CORRECTING PROBLEMS IN EARTH CIRCUITS
Once a high resistance condition in a earth circuit has been located, you must determine the actual cause.
If the problem is at a connector, check for bent, corroded, or loose connector terminals. 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, bolt, or sheet metal screw, check for corrosion, paint, or loose connections. Paint can
be a very good insulator; good conductors, not insulators are needed for electrical connections.
Corrosion, paint, and other causes of resistance should be removed using a wire brush and/or emery cloth.
When assembling earth wire’s eyelet on earth points, be sure an external type star washer is placed below the
wire eyelet(s). If the system is marginal, you can also place a star washer between the nut or the sheet- metal sc rew
and the top wire eyelet. Tighten the fastener to specification, making sure the star washer digs through any paint
into the mounting surface. Star washers also lock the fastener in place, preventing it from loosening.
All 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 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.