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 for correct workshop practices with regard to safety and/or property damage.
CONTENTS
GENERAL DESCRIPTION
PCM/PIM
ENGINE GROUND LOCATIONS
SYMPTOMS
IMPORTANT PRELIMINARY CHECKS BEFORE STARTING
INSPECTION
INTERMITTENTS
HARD START
SURGES/CHUGGLES
LACK OF POWER, SLUGGISHNESS OR SPONGINESS
DETONATION/SPARK KNOCK6
HESITATION, SAG, STUMBLE
CUTS OUT, MISSES
POOR FUEL ECONOMY
ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING
DIESELING, RUN-ON
BACKFIRE
RESTRICTED EXHAUST SYSTEM CHECK
TESTING GROUNDS
BASICS
SENSOR CIRCUIT GROUND SENSITIVITY – AN EXAMPLE
GROUND CIRCUITS
PARALLEL GROUNDS
CHECKING GROUNDS
SOLID-STATE CIRCUIT VOLTAGE DROP SPECIFICATIONS
GROUND CREDIBILITY CHECK
CORRECTING PROBLEMS IN GROUND CIRCUITS
GENERAL DES CRIP TION
W hen no diagnostic trouble codes have been set and the Tech 2 data values ar e 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 this Section.
PCM / PIM
As the PCM and PIM can have a failure that may affect only one circuit, by following the Diagnostic Procedures in
this Section, which circuit has a problem and where it is, will be determined.
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 can occur.
ENGINE GROUND LOCATIONS
Figure 6C3-2B-1 – Engine Powertrain Wiring Harness to Engine Assembly Ground Location.
Legend
1. Knock Sensors Jumper Harness Connector
2. PCM Ground Location Left Rear Head 3. PCM Ground Location Right Front Head
4. PCM Wiring Harness to A/C Compressor
SYMPTOMS
IMPORTANT PRELIMINARY CHECKS BEFORE STARTING
Perform the Powertrain OBD Sy stem Check before using the System Tables, and verify all of the following are true:
• The PCM/PIM and MIL (Malfunction Indicator Lamp) are operating correctly.
• There are no PCM or PIM DTC(s) stored.
• Ensure that the engine coolant tem perature is not above 130° C. This condition causes the PCM to operate in
Engine Coolant O ver Temperature- Fuel Dis abled Mode. While in this Mode, the PCM tur ns the f uel O F F to f our
cylinders at a time in order to k eep engine temperature f rom reaching dam aging levels. The system perceives
Engine Coolant Over Temperature as a lack of power, miss, or rough idle. If the vehicle is operating in Engine
Coolant Over Temperature-Fuel Disabled Mode, refer to Section 6B-3 ENGINE COOLING – GEN III V8
ENGINE, for diagnosis.
• The Tech 2 data is within the normal operating range, refer to Section 6C3-2 DIAGNOSIS – GEN III V8
ENGINE.
• 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 in this Section, require a careful visual and physical inspection. This step is
extremely important, as it can lead to correcting a problem without further checks and can save valuable time.
This check includes:
• The PCM/PIM grounds 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 Mass Air Flow (MAF) sensor installation.
• 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 f or im proper installation of electric al com ponents if an interm ittent c ondition exists. Inspect for
afterm arket thef t deterrent devices, lights and cellular phones. Ensure that no aftermarket equipment is connected
to the Class II cir cuit. If you c an not locate an intermittent c ondition, a cellular phone signal com munication m ay be
the cause of the condition.
IMPORTANT: T he problem may or m ay 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.
1. 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 ensure proper contact tension.
• Poor terminal to wire connection requires removing the terminal from the connector body in order to check.
• Road test the vehicle with a Digital Multimeter (DMM) connected to the suspected circuit. An abnormal
voltage when the malfunction occurs is a good indication that there is a malfunction in the circuit being
monitored.
2. Use Tech 2 to help detect intermittent conditions. Tech 2 has several features that you can use to locate an
intermittent condition. Use the following features to find intermittent faults:
• You can trigger the Snapshot feature in order to capture and store engine parameters within the scan tool
when the m alfunction occurs. You can then review this stored inform ation in order to see what caused the
malfunction.
• Using the Scan Tool’s Freeze Frame/Failure Records can also aid in locating an intermittent condition.
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 intermittent condition exists as a start and then stall condition, check for DTCs relating to the
theft deterrent system. Check for improper installation of electrical options such as lights, cellular phones etc.
3. Any of the following may cause an intermittent Malfunction Indicator Lamp (MIL) with no stored DTC:
• The ignition coils shorted to ground, arcing at the ignition wires or the spark plugs.
• The PCM/PIM grounds, refer to Section 12P WIRING DIAGRAMS.
• The Ignition Control (IC) wires for being routed too close to the secondary 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 any other open diodes, refer to
Section 12P WIRING DIAGRAMS.
4. 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
• Dieselling, Run-On
• Backfire
HARD START
DEFINITION: ENGINE CRANKS OK, BUT DOES NOT START FOR A LONG TIME. DOES EVENTUALLY RUN, MAY START
BUT STALLS IMMEDIATELY.
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting, in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to Section 12P WIRING DIAGRAMS.
• Refer to Service Techlines 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 c old engine. The ECT and IAT Sensor values should be within ± 3° C
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 Table for
resistance specifications. Replace the ECT Sensor if the resistance is not within
the spec if ic ation. If the s ens or is within the specification, repair ECT s ignal c irc uit
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 Replace in
6C3-3 SERVICE OPERATIONS.
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 6C3-2A DIAGNOSTIC TABLES.
• A faulty fuel pump in-tank check valve, slows down the fuel drain back to the
tank after the engine stops. To check for this condition, refer to Fuel System
Diagnosis in 6C3-2A DIAGNOSTIC TABLES.
• 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 ground.
• Check for a low fuel pressur e condition. Refer to F uel System Diagnosis in 6C3-
2A DIAGNOSTIC TABLES.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in 6C3-2A
DIAGNOSTIC TABLES.
• Check for a contaminated fuel condition.
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 ground.
• Check for proper ignition voltage output with spark tester J 26792 or equivalent.
Refer to 6C3-3 SERVICE OPERATIONS.
• Remove the spark plugs and check for the following:
– Wet plugs
– Cracks
– Wear
– Incorrect gap
– Burned electrodes
– Heavy deposits
• Determ ine the c auses of the fouling befor e replac ing the spark plugs, if the spark
plugs are fuel or oil fouled.
• Check for bare or shorted ignition wires.
• Check for loose ignition coil grounds.
• Check the spark plugs for proper heat range.
Refer to 6C3-3 SERVICE OPERATIONS.
Checks Actions
Engine Mechanical • Excessive oil in combustion chamber - leaking valve seals. Refer to 6A3
ENGINE MECHANICAL– GEN III V8 ENGINE.
• Low cylinder compression. Refer to 6A3 ENGINE MECHANICAL– GEN III V8
ENGINE.
• 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; cylinders, camshaft, pistons, etc.
Refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE.
SURGES/CHUGGLES
DEFINITION: ENGINE POWER VARIATION UNDER STEADY THROTTLE OR CRUISE. VEHICLE SPEEDS UP AND SLOWS
DOWN WITH NO CHANGE IN THE ACCELERATOR PEDAL POSITION.
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant 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 pressur e condition. Refer to F uel System Diagnosis in 6C3-
2A DIAGNOSTIC TABLES.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in 6C3-2A
DIAGNOSTIC TABLES.
• 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 c ause an engine to run rich ( long term f uel trim near 13%).
For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1
Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
• 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 Cir cuit Low Voltage Bank
1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1
Ignition System • W et down the secondary ignition system with water from a spray bottle. W etting
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, or equivalent.
• 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. Refer to 6C3-3 SERVICEOPERATIONS.
• 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 6C3-2A DIAGNOSTIC TABLES, for
diagnosis of the rich condition
• For oil fouling refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, for
diagnosis of the oil fouling condition.
• Check for loose ignition coil grounds.
• Check the spark plugs for proper heat range. Refer to 6C3-3 SERVICE
OPERATIONS.
Checks Actions
Engine Mechanical • Ensure that the engine coolant temperature is not above 130° C. This condition
causes the PCM to operate in Engine Coolant Over Temperature-Fuel Disabled
Mode. W hile in this Mode, the PCM turns f uel 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 Dis abled Mode, ref er to 6B3 ENG INE COO LING – G EN III V8
ENGINE.
Additional Checks • Inspect vacuum hoses for splits, kinks, proper connections and routing.
• Check the Torque Converter Clutch (TCC) operation. A TCC that applies too
soon can cause the engine to detonate. Refer to 6C3-2A DIAGNOSTIC
TABLES.
LACK OF POWER, SLUGGISHNESS, OR SPONGINESS
DEFINITION: .ENGINE DELIVERS LESS THAN NORMAL POWER. LITTLE OR NO INCREASE IN SPEED WHEN THE
ACCELERATOR PEDAL IS PARTIALLY DEPRESSED.
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant information.
• Remove the air filter element and check for dirt or for being restricted. Refer to
Air Cleaner Elem ent Replace in 6C3-3 SERVICE OPERATIONS and replace as
necessary.
Sensor/System • Use Tech 2 to monitor the knock sensor system for excessive spark retard
activity. Refer to 6C3-2A DIAGNOSTIC TABLES
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 ground.
• Check for a low fuel pressure condition. Refer to 6C3-2A DIAGNOSTIC
TABLES.
• Check for a restricted fuel filter. Refer to 6C3-2A DIAGNOSTIC TABLES.
• Check for a contaminated fuel condition.
• Check the items that c ause an engine to r un ric h (long ter m fuel tr im near -13%) .
For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1
Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean c ondition, refer to DTC P0131 HO 2S Circuit High Voltage Bank
1 Sensor 1 and DTC P0151 HO2S Circuit High Voltage Bank 2 Sensor 1.
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 ground.
• W et down the secondary ignition system with water from a spray bottle. W etting
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 correc t ignition voltage output with s park tester J 26792 or equivalent.
Refer to Electronic Ignition System Diagnosis in 6C3-2C FUNCTIONAL
CHECKS.
• 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. Refer to 6C3-3 SERVICE OPERATIONS.
• 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 6C3-2A DIAGNOSTIC TABLES, for
diagnosis of the rich condition.
• For oil fouling refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, for
diagnosis of the oil fouling condition.
• Check for loose ignition coil grounds.
• Check the spark plugs for proper heat range. Refer to 6C3-3 SERVICE
OPERATIONS.
Checks Actions
Engine Mechanical • Ensure that the engine coolant temperature is not above 130° C. This condition
causes the PCM to operate in Engine Coolant Over Temperature-Fuel Disabled
Mode. W hile in this Mode, the PCM turns f uel 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 6B3 ENGINE COOLING – GEN III
V8 ENGINE.
• Excessive oil in combustion chamber - leaking valve seals. Refer to 6A3
ENGINE MECHANICAL – GEN III V8 ENGINE.
• Low cylinder compression. Refer to 6A3 ENGINE MECHANICAL – GEN III V8
ENGINE, for diagnosis.
• For incorrect basic engine parts. Inspect the following:
– Camshaft
– Cylinder head/s
– Pistons, etc.
• Refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE, 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 6C3-2A
DIAGNOSTIC TABLES
DETONATION/SPARK KNOCK
DEFINITION: .A MILD TO SEVERE PING, USUALLY WORSE UNDER ACCELERATION. THE ENGINE MAKES SHARP
METALLIC KNOCKS THAT CHANGE WI TH THROTTLE OPENING.
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant information.
• If T ech 2 readings are norm al (refer to the supporting text of the Powertrain On-
Board Diagnostic (OBD) System Check) and there are no engine mechanical
faults, f ill the fuel tank with a premium petrol that has a m inim um octane reading
of 92 and re-evaluate the vehicle’s performance.
Fuel System • Check for a low fuel pressur e condition. Refer to F uel System Diagnosis in 6C3-
2A DIAGNOSTIC TABLES.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis.
• Check for a contaminated fuel condition.
• Check the items that c ause an engine to r un ric h (long ter m fuel tr im near -13%) .
For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1
Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean c ondition, refer to DTC P0131 HO 2S 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 6C3-3 SERVICE
OPERATIONS.
Engine Mechanical Check for the following engine mechanical problems:
• Exces sive oil in com bustion c hamber- leaking valve seals . Refer to 6A3 ENG INE
MECHANICAL – GEN III V8 ENGINE.
• Low cylinder c ompr ession. Refer to Sec tion 6A3 ENGINE MECHANICAL – GEN
III V8 ENGINE
• 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 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE.
Additional Checks • Check the Park/Neutral Position (PNP) switch operation. Refer to 7C4
AUTOMATIC TRANSMISSION – ON-VEHICLE SERVICING
• Check the TCC operation. The TCC applying too soon can cause the engine to
spark knock. Refer to 6C3-2A DIAGNOSTIC TABLES.
HESITATION, SAG, STUMBLE
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
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant information.
Sensor/System • Check the MAP sensor operation. Refer to 63-2A DIAGNOSTIC TABLES
Fuel System • Check for a low fuel pressur e condition. Refer to F uel System Diagnosis in 6C3-
2A DIAGNOSTIC TABLES.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in 6C3-2A
DIAGNOSTIC TABLES.
• 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 ground.
• Perfor m the injector balance test. Ref er to Fuel Injector Balanc e Test in 6C3-2C
FUNCTIONAL CHECKS.
• Check the items that c ause an engine to r un ric h (long ter m fuel tr im near -13%) .
For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1
Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean c ondition, refer to DTC P0131 HO 2S Circuit High Voltage Bank
1 Sensor 1 and DTC P0151 HO2S Circuit High Voltage Bank 2 Sensor 1.
Ignition System • W et down the secondary ignition system with water from a spray bottle. W etting
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 ground.
• Check for proper ignition voltage output with spark tester J 26792 or equivalent.
Refer to Electronic Ignition System Diagnosis in 6C3-2C FUNCTIONAL
CHECKS.
• Remove the spark plugs and check for the following:
– Wet plugs
– Cracks
– Wear
– Incorrect gap
– Burned electrodes
– Heavy deposits
• An Incor rect spar k plug gap will cause a driveablitiy problem. Set the s park plug
gap using a wire gauge gap tool. Refer to 6C3-3 SERVICE OPERATIONS.
• 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 6C3-2A DIAGNOSTIC TABLES, for
diagnosis of the rich condition.
• For oil fouling refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE for
diagnosis of the oil fouling condition.
• Check for loose ignition coil grounds.
• Check the spark plugs for proper heat range. Refer to 6C3-3 SERVICE
OPERATIONS.
Checks Actions
Engine Cooling
Sy stem • Check the engine thermostat for proper operation and for proper heat range.
Refer to 6B3 ENGINE COOLING – GEN III V8 ENGINE.
Additional Checks • Check the generator output voltage. Refer to 6D3-1 CHARGING SYSTEM.
Repair the charging s ystem if the generator output voltage is less than 9 volts or
more than 16 volts
CUTS OUT, MISSES
DEFINITION: .STEADY PULSATION OR JERKING THAT FOLLOW S 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.
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant information.
• Remove the air filter element and check for dirt or for being restricted. Refer to
Air Cleaner Elem ent Replace in 6C3-3 SERVICE OPERATIONS and replace as
necessary
Sensor/System • Use Tech 2 to monitor the knock sensor system for excessive spark retard
activity. Refer to 6C3-2A DIAGNOSTIC TABLES.
Fuel System • Perfor m the injector balance test. Ref er to Fuel Injector Balanc e Test in 6C3-2C
FUNCTUONAL CHECKS for procedure.
• Check for a low fuel pressur e condition. Refer to F uel System Diagnosis in 6C3-
2A DIAGNOSTIC TABLES.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in 6C3-2A
DIAGNOSTIC TABLES.
• Check the items that c ause an engine to r un ric h (long ter m fuel tr im near -13%) .
For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1
Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean c ondition, refer to DTC P0131 HO 2S Circuit High Voltage Bank
1 Sensor 1 and DTC P0151 HO2S Circuit High Voltage Bank 2 Sensor 1.
Ignition System • W et down the secondary ignition system with water from a spray bottle. W etting
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 or equivalent.
Refer to Electronic Ignition System Diagnosis in 6C3-2C FUNCTIONAL
CHECKS.
• 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. Refer to 6C3-3 SERVICE OPERATIONS.
• 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 6C3-2A DIAGNOSTIC TABLES, for
diagnosis of the rich condition.
• For oil fouling refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE for
diagnosis of the oil fouling condition.
• Check for loose ignition coil grounds.
• Check the spark plugs for proper heat range. Refer to 6C3-3 SERVICE
OPERATIONS.
• Inspect the Secondary ignition for the following:
– Ignition wires for cross firing
– Ignition wires arcing to ground
– 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 rocker 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 6A3 ENGINE MECHANICAL.
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.
• Electrom agnetic Interf erence (EMI) on the r eference c ircuit can caus e 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 manif old and the exhaust manifold passages for casting flash.
Refer to in 6A3 ENGINE MECHANICAL.
POOR FUEL ECONOMY
DEFINITION: FUEL ECONOMY, AS MEASURED BY AN ACTUAL ROAD TEST, IS NOTICEABLY LOWER THAN NORMAL. .
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant 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?
Sensor/System • Check the air intake system and crankcase for air leaks.
• Check the PCV System f or corr ect operation. Plac e 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, command vehicle
speed output. Speedometer should read same as Tech 2 output. If not, refer to
12C INSTRUMENTS.
• Use Tech 2 to monitor the knock sensor system for excessive spark retard
activity. Refer to 6C3-2A DIAGNOSTIC TABLES.
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 6C3-2
FUNCTIONAL CHECKS.
• Check for a low fuel pressur e condition. Refer to F uel System Diagnosis in 6C3-
2A DIAGNOSTIC TABLES.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in 6C3-2A
DIAGNOSTIC TABLES.
• 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 inj ectors that are shor ted internally. Com pare the injector res istances.
Injector r es istanc e should be within one ohm of each other. Refer to Fuel Inj ec tor
Coil Test - ECT Between 10 – 35° C in 6C3-2 FUNCTIONAL CHECKS.
• 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 c ause an engine to r un ric h (long ter m fuel tr im near -13%) .
For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1
Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean c ondition, refer to DTC P0131 HO 2S Circuit High Voltage Bank
1 Sensor 1 and DTC P0151 HO2S Circuit High Voltage Bank 2 Sensor 1.
Checks Actions
Ignition System • Check for proper ignition voltage output with spark tester J 26792 or equivalent.
Refer to Electronic Ignition System Diagnosis in 6C3-2C FUNCTIONAL
CHECKS.
• 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. Refer to 6C3-3 SERVICE OPERATIONS.
• 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 6C3-2A DIAGNOSTIC TABLES, for
diagnosis of the rich condition.
• For oil fouling refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE for
diagnosis of the oil fouling condition.
• Inspect the Secondary ignition for the following:
– Ignition wires arcing to ground
– Ignition wires for proper routing
• W et down the secondary ignition system with water from a spray bottle. W etting
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 loose ignition coil grounds.
Engine Cooling
Sy stem • Check the engine coolant level f or being low. Refer to 6B3 ENG INE COOLING –
GEN III V8 ENGINE.
• Check the engine therm ostat f or proper operation and for the correct heat range.
Refer to 6B3 ENGINE COOLING – GEN III V8 ENGINE.
Engine Mechanical • Check engine mechanical for the following:
– Check compression
– Sticking or leaking valves
– Worn camshaft lobes
– Valve timing
– Bent push rods
– Worn rocker 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 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE
Checks Actions
Additional Checks • Check the vacuum hoses for splits, kinks, and proper connections.
• Check the TCC operation. Tech 2 should indicate an RPM drop, when the
system commands the TCC ON. Refer to 6C3-2A DIAGNOSTIC TABLES.
• 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.
• Electrom agnetic Interf erence (EMI) on the r eference c ircuit can caus e 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 P/N switch circuit. Refer to 6C3-2A DIAGNOSTIC TABLES.
• Check for faulty engine mounts. Ref er to 6A3 ENGINE MECHANICAL – GEN III
V8 ENGINE for inspection of mounts.
• Check the intake and the exhaust manifold passages for casting flash. Refer to
6A3 ENGINE MECHANICAL.
ROUGH, UNSTABLE, OR INCORRECT IDLE , S TALLING
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..
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant information.
• Remove and check the air filter elem ent for dirt, or for being restricted. Refer to
Air Cleaner Element Replace in 6C3-3 SERVICE OPERATIONS. Replace as
necessary.
Sensor/System • Check the PCV System f or cor rec t oper ation. Plac e a f inger over inlet hole of the
valve end several times. valve should snap back. If not, replace the valve.
• Use Tech 2 to monitor knock sensor system for excessive spark retard activity.
Refer to 6C3-2A DIAGNOSTIC TABLES.
Fuel System • Perfor m the injector balance test. Ref er to Fuel Injector Balanc e Test in 6C3-2C
FUNCTIONAL CHECKS for this procedure.
• Check for a low fuel pressur e condition. Refer to F uel System Diagnosis in 6C3-
2A DIAGNOSTIC TABLES.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in 6C3-2A
DIAGNOSTIC TABLES.
• 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 c ause an engine to r un ric h (long ter m fuel tr im near -13%) .
For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1
Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.
• Check the items that can cause an engine to run lean (long term fuel trim near
23%). For a lean c ondition, refer to DTC P0131 HO 2S Circuit High Voltage Bank
1 Sensor 1 and DTC P0151 HO2S Circuit High Voltage Bank 2 Sensor 1.
Ignition System • Check for proper ignition voltage output with spark tester J 26792 or equivalent.
Refer to Electronic Ignition System Diagnosis in 6C3-2C FUNCTIONAL
CHECKS.
• 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. Refer to 6C3-3 SERVICE OPERATIONS.
• 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 6C3-2A DIAGNOSTIC TABLES, for
diagnosis of the rich condition.
• For oil fouling refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE for
diagnosis of the oil fouling condition.
• Inspect the Secondary ignition for the following:
– Ignition wires arcing to ground
– Ignition wires for proper routing
• W et down the secondary ignition system with water from a spray bottle. W etting
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 loose ignition coil grounds.
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 rocker 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 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE
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.
• Electrom agnetic Interf erence (EMI) on the r eference c ircuit can caus e 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 P/N switch circuit. Refer 6C3-2A DIAGNOSTIC TABLES
• Check for faulty engine mounts. Ref er to 6A3 ENGINE MECHANICAL – GEN III
V8 ENGINE ofor inspection of the mounts.
• Check the intake and the exhaust manifold passages for casting flash. Refer to
6A3 ENGINE MECHANICAL – GEN III V8 ENGINE.
DIESELING, RUN-ON
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.
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant 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
6C3-2A DIAGNOSTIC TABLES for this procedure.
BACKFIRE
DEFINITION: FUEL IGNITES IN THE INTAKE MANIFOLD OR IN THE EXHAUST SYSTEM, MAKING A LOUD POPPING
NOISE.
Checks Actions
Preliminary • Refer to SYMPTOMS, Important Preliminary Checks Before Starting in this
Section.
• Check the PCM/PIM grounds f or being clean, tight and in their proper locations.
Refer to 12P WIRING DIAGRAMS.
• Refer to Service Techlines for relevant information.
Sensor/System • Check the air intake system and crankcase for air leaks.
• Check the PCV System f or corr ect operation. Plac e 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, command vehicle
speed output, speedometer should read same as Tech 2 output. If not, refer to
12C INSTRUMENTS.
• Use Tech 2 to monitor the knock sensor system for excessive spark retard
activity. Refer to 6C3-2A DIAGNOSTIC TABLES.
Fuel System • Check for a low fuel pressur e condition. Refer to F uel System Diagnosis in 6C3-
2A DIAGNOSTIC TABLES.
• Check for a restricted fuel filter. Refer to Fuel System Diagnosis in 6C3-2A
DIAGNOSTIC TABLES.
• 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.
Ignition System • Check for proper ignition voltage output with spark tester J 26792 or equivalent.
Refer to Electronic Ignition System Diagnosis in 6C3-2C FUNCTIONAL
CHECKS.
• Check for an intermittent ignition system malfunction in the following circuits:
– Intermittent ignition control circuit.
– Use the Tech 2 Snapshot feature 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. Refer to 6C3-3 SERVICE OPERATIONS.
• 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 6C3-2A DIAGNOSTIC TABLES, for
diagnosis of the rich condition.
• For oil fouling refer to 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE for
diagnosis of the oil fouling condition.
• Inspect the Secondary ignition for the following:
– Ignition wires for cross firing
– Ignition wires arcing to ground
– Ignition wires for proper routing
• W et down the secondary ignition system with water from a spray bottle. W etting
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 loose ignition coil grounds.
Checks Actions
Engine Cooling
Sy stem • Check the engine coolant level f or being low. Refer to 6B3 ENG INE COOLING –
GEN III V8 ENGINE.
• Check the engine therm ostat f or proper operation and for the correct heat range.
Refer to 6B3 ENGINE COOLING – GEN III V8 ENGINE.
Engine Mechanical • Check engine mechanical for the following:
– Check compression
– Sticking or leaking valves
– Worn camshaft lobes
– Valve timing
– Bent push rods
– Worn rocker 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 6A3 ENGINE MECHANICAL – GEN III V8 ENGINE
Additional Checks • Check the vacuum hoses for splits, kinks, and proper connections.
• Check the TCC operation. Tech 2 should indicate an RPM drop, when the
system commands the TCC ON. Refer to 6C3-2A DIAGNOSTIC TABLES.
• 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.
• Electrom agnetic Interf erence (EMI) on the r eference c ircuit can caus e 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 P/N switch circuit. Refer 6C3-2A DIAGNOSTIC TABLES
• Check for faulty engine mounts. Ref er to 6A3 ENGINE MECHANICAL – GEN III
V8 ENGINE ofor inspection of the mounts.
• Check the intake and the exhaust manifold passages for casting flash. Refer to
6A3 ENGINE MECHANICAL – GEN III V8 ENGINE.
RESTRICTED EXHAUST SYSTEM CHECK
STEP ACTION VALUE YES NO
1. Was the "On-Board Diagnostic" (OBD) System Check
performed? Go to Step 2 Go to
OBD System
Check
in this Section.
2. 1. Carefully remove the HO2S for Bank 1
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 Go to Step 5 Go to Step 3
3. 1. The Exhaust Back Pressure tester 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 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.
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 Go to Step 6 Go to Step 5
5. 1. The Exhaust Back Pressure tester 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 Go to Step 6 No Exhaust
Restrictions
found. If a
driveability
symptom exists,
refer to 6C3-2C
SYMPTOMS
6. 1. 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 GROUNDS
Unusual displays in the instrument, lamps that are dim or flash unexpectedly, stop lamps that come on when the
indicators are used, are all classic symptoms of ground problems.
This section discusses the importance of good ground circuits and starts by explaining some basic theory. Then, the
diagnosis of a solid-state circuit ground condition is detailed, to help show how to correct a problem, should it occur.
BASICS
For a circuit to operate properly, three things are
needed:
a. A good power supply to components;
b. Good components and,
c. Sound ground circuits.
Circuits are complete systems; current must flow
from beginning to end as des igned, not hinder ed by
unexpected resistance anywhere in the circuit.
While some Technicians realise that the power
supply to a circuit must be free of unwanted
resistance, they can have difficulty in visualising
why a ground cir cuit mus t also be fr ee of unwanted
resistance.
For current to flow, the circuit must be complete; it
must pass through and out of a component like
water flowing thr ough a bathtub. With a free f lowing
tub (no plug inserted), the water can flow out as
freely as it flows in. In electrical term s , current m ust
also enter and leave components freely, if they are
to perform as they are designed.
Figure 6C2-2B-2
Sensitive, solid-s tate systems have their own ground points; high c urrent devic es (e.g. m otor s) do not ground 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, two different types of different ground
location systems are used. An exam ple is the use of a dedicated wire to connec t an isolated ground junction bloc k
to the battery negative terminal. This wire reduces the effect of spikes on sensitive circuits at the ground junction
block.
Solid-state circuits are particularly sensitive to poor circuit continuity because, in most cases, they use low current
flow. T his Sec tion on ground c irc uits , c oncer ns itself with one solid-state devic e; the PCM. However, the inf or mation
included here can also be applied to all solid-state ground circuits.
Severe restrictions (i.e. resistance) in the ground circuit can cause resets and intermittent codes to set, in solid-state
systems. The PCM operates devic es such as fuel injec tors, idle air control (IAC), etc., and receives inputs from low
voltage sensors, such as the manifold absolute pressure sensor (MAP), crankshaft speed/position (CKP). These
input and output devices need good circuitry for correct operation.
Remember that, when maladjusted or imperfect sensors cause values to shift, they are usually accompanied by
driveability problems. If there is excessive resistance in the ground circuit, then 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 vehicle efficiency and performance and may be noticed by the
customer.
SENSOR CIRCUIT GROUND SENSITIVITY – AN EXAMPLE.
Looking at the Throttle Position (TP) sensor circuit will provide an example of how a little resistance in the ground
circuit can cause problems. Figure 6C2-2B-3 shows a throttle position sensor (1) first with a good ground circuit (‘A’)
and then with a poor c onnection (‘B’) in the ground cir cuit. Refer to this illustration, as you proceed through the text
that follows:
First, the throttle position sensor consists of a resistor and a wiper and, one terminal of the resistor is connected to a
supply voltage (5 V) , while the other is connected to ground. As the wiper moves ac ross the r esistor, the voltage of
the wiper terminal progressively changes, with a change in the throttle position. If the wiper is near the supply
voltage end of the resistor, the wiper output will approach the supply voltage (over 4.5 volts at wide open throttle).
As the wiper m oves toward the grounded 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). Note though, that the actual closed and wide open throttle
voltage specifications may vary for different engines. Also, the sensor output should never be greater than reference
supply voltage or less than 0.20 volts. (The PCM would set a DTC, should this situation occur.)
Figure 6C2-2B-3
In the f ir st example with a good ground circ uit (‘A’), the TP sens or (1) is shown with the wiper in the closed throttle
position. T he total voltage acros s the r esistor in the TP sens or is 5 volts. T he voltage drop fr om the res istor sourc e
voltage terminal to the wiper is 4.5 volts. The voltage drop from the wiper to the resistor ground 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 sensor with the bad signal caused by resistance in the ground circuit. The throttle position stays the
sam e but the sens or output voltage changes . In this exam ple the increased resis tance causes an additional voltage
drop of 0.5 volts. The voltage drop from the wiper to ground 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 f rom the TP sensor . T his is not a good value (in this ex ample) of a
closed throttle.
Now you can see why good earths are needed and how sensitive some circuits can be.
GROUND CIRCUITS
How do you know which wires are ground wires, which connectors they go through, and whether they are connected
to a ground junction or the body?
Section Section 12P, WIRING DIAGRAMS should be used whenever you are diagnosing any electrical condition,
including earths. The individual circuits show the power and ground circuits for components in specific systems.
If you suspec t s everal c ircuits are being af f ected by a poor or a bac k -feed to gr ound, look at the circuits to see how
the systems might interact. If they have any common ground wires, that is where you should start diagnosis.
Back -feeding is when current, s eeking ground, f eeds back through inac tive circuits (the revers e direc tion of normal
current flow) to find a path to ground. This can only happen when the active circuit (needing a ground) shares a
disconnected or poor ground with an inactive circuit and the voltage supply side of the inactive circuit feeds other
components with good earths.
PARALLEL GROUNDS
Some solid-state com ponents use redundant ground circuits. That is, they have more than one wire connecting to
ground. The PCM has more than one ground 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 m anaged 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. The simple example shown,
proves this to be true and holds for even the small
resistance's in wires.
It follows that parallel wires provide the lowest
resistance. Because of them, in many solid-state
systems a problem with one of the ground wires
would not affect the circuit; the redundant wires
could handle the current load. For other solid-state
systems the loss of even one redundant ground
may affect operation, but the remaining ground
wire(s) may allow the vehicle to be driven.
Figure 6C2-2B-4
An example that can be difficult to locate, follows:
Symptom: A vehicle has driveability problems. However, whenever Tech 2 is hooked up and the vehicle tested,
none of the complaint symptoms are displayed.
Cause: T he PCM earths ar e not providing a good gr ound, henc e the res ulting dr iveability condition. When Tec h 2 is
connected to the vehicle, a good gr ound path is provided for the PCM through the Data Link Connector (DLC). T he
DLC uses a dif ferent ground than the PCM. Always test for dr iveability symptom s befor e hooking up Tec h 2. If they
disappear when Tech 2 is hooked up, check the ground circuit for continuity.
The severity of the sym ptom (s) is propor tional to the severity of the problem in the ground circ uit. 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
open in the ground circuit.
CHECKING GROUNDS
Once you determine that the cause of the vehicle sym ptom(s) m ay be caused by a bad ground, it is tim e to check
for poor ground with one more tool: a high-impedance multimeter set to DC Volts.
The best way to check for poor ground connections in low-current solid-state circuits is to check the voltage drop.
To do this you need a high-im pedance digital m ultimeter (DMM) rated at a minim um of 10 m egaohm s (10,000,000
ohms) per volt. Any DMM with less impedance than this can affect the circuit being tested and also give an incorrect
reading.
Start by checking the entire suspect ground circuit. With the DMM set on the 2 Volt DC scale, connect the black
negative lead to the battery negative (ground) term inal. (If you are using an auto-ranging m eter, simply set it to the
DC volts setting.)
Connect the red positive lead of the DMM to the ground terminal of the component to be tested. With the circuit
activated, check the voltage drop in the circuit. If the voltage reading is within specific ations, look f or a caus e other
than a poor ground at this component.
If the voltage drop reading is too high, proceed by isolating the cause of the high voltage drop. Move the positive
lead to the next connection in the ground circuit, working closer to the source voltage. (Keep the negative lead
connected to the battery negative terminal.) Be sure to check both sides of each in-line connector and both the
eyelet and the stud or screw at ground points. Repeat this process through the ground path until the voltmeter
reading is within specifications. The high resistance causing the ground problem is located between where you
obtained a good reading and the last high reading.
When a circuit uses redundant grounds be sure to check all the ground 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-state component before going to ground (such as the IAT sensor circuit
between the IAT 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 ground circuit anywhere in the ground path at or after the
solid-state component (such as the PCM ground circuits to the engine block ground points), the maximum allowable
measured voltage is 0.020 volts (20 millivolts). If you measure a voltage above specifications, repair the ground
circuit.
ACCEPTABLE VOLTAGE DROP READINGS
BETWEEN SENSOR AND PCM 0.060 V (60 mV)
BETWE E N P CM AND BATTERY NEGA TI V E TERMINAL 0. 020 V (20 mV)
Checking the Voltage Drop in a Solid-State Sensor
Circuit – An Example.
Look again at a IAT sensor circuit. With the voltm eter negative lead c onnected to the negative battery terminal and
the ignition switched ON, check the voltages at various points between the IAT sensor pin "A" and pin "X1-80" of the
PCM. A voltage reading of 0.060 volts or less with the meter positive lead at the IAT sensor B64, terminal X1-A,
indicates that the entire ground circuit from the IAT sensor to the battery is continuous and sufficiently low in
resistanc e. A voltage r eading of 0.060 volts at "the splic e" or the PCM connec tor A84-X 2, ter minal X2- 57 would also
be within specifications.
When voltage measurements are made in the ground 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 ground points.
Figure 6C3-2B-5 Testing Voltage Drop Before and After the PCM
Legend
A. Voltage Drop Testing Before the PCM
1. Voltage Reading to be 0.060 Volt, Maximum B. Voltage Drop Testing After the PCM
2. Voltage Reading to be 0.020 Volt, Maximum
GROUND CREDIBILITY CHECK
Figure 6C3-2B-6 – Engine Coolant Temperatire Sensor Circuit
CIRCUIT DESCRIPTION:
The ground c r edibility check can be either us ed at the beginning of all diagnos tic pr oc edures or it can be used when
no diagnostic trouble codes are set, but a sy mptom still exists.
TEST DESCRIPTION:
NOTE: The number(s) below refer to the step number(s) on the diagnostic table.
1. To properly test the voltage drop of the powertrain control module system ground,a load must be present on the
circuit. Using Tech 2, select ‘Canister Purge’. By turning "ON" the Purge solenoid, this will cause a sufficient
current draw on the system for testing.
2. Check connectors in ground 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 (PCM) operates on such a small current, even a minor corrosion problem
will cause problems with the system.
Make sure the grounds are clean and tight. Remember a good ground is about 25% of the total system circuit.
Normally you will check the wiring for; power, continuity, the load, but rarely check the ground. PCM system grounds
are very important to proper operation.
A84–X1 (BLUE) B39
Figure 6C3-2A-7
GROUND CREDIBILITY CHECK
STEP ACTION VALUE YES NO
1. Was the "On-Board Diagnostic" (OBD) System Check
performed? Go to Step 2 Go to
OBD System
Check
in this Section.
2. 1. Ignition OFF.
2. Disconnect ECT sensor connector, B39.
3. Using a DMM set to DC voltage scale, connect
negative lead to ground cable at battery and connect
positive lead to the GY/BK wire at the IAT sensor
connector, B39, terminal X1-A.
4. Ignition ON.
5. Using Tech 2, select ‘Canister Purge’.
6. Turn ‘ON’ Canister Purge with ‘Soft’ 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 ground
terminals and connection.
2. Reassemble the PCM ground terminals.
Is action complete?
Verify Repair –
CORRECTING PROBLEMS IN GROUND CIRCUITS
Once a high resistance condition in a ground 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 assem bling gr ound wire’s eyelet on ground 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 scr ew
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 ground wire eyelet or star washer to the
mounting surface and stops. Repair any stripped ground fasteners.
IMPORTANT: Do not over-tighten sheet-metal screws. Over-tightening can enlarge the hole and create a bad
ground. If the sheet-metal is enlarged, the screw will continue to turn. Either close the hole using a dolly and
hammer or drill a new correctly sized hole for the screw.