Intermittent
| IMPORTANT | Inspect for improper installation of electrical components if an intermittent condition exists. Inspect for aftermarket theft deterrent devices, lights, and cellular phones. Verify that no aftermarket equipment is connected to the class 2 circuit. If you can not locate an intermittent condition, a cellular phone communication signal may cause the condition. |
| IMPORTANT | The condition may or may not turn ON the MIL or store a DTC. |
Faulty electrical connections or wiring cause most intermittent conditions. Perform a careful visual and physical inspection of the suspect connectors for the following conditions
- Improperly mated connector halves
- Terminals that are not seated
- Terminals that are damaged or improperly formed
Reform or replace connector terminals in the affected circuit to ensure proper contact tension. Refer to Connector Repairs . Remove the terminal from the connector body in order to inspect for poor terminal wire connection. Refer to Testing for Intermittent Conditions and Poor Connections .
Road test the vehicle with the DMM connected to the suspected circuit. An abnormal reading that is observed when the symptom occurs is a good indication that there is a malfunction in the circuit being monitored.
Use a scan tool to help detect intermittent conditions. Useful features of the GM Techline scan tool include the following
- Trigger the Snapshot feature in order to capture and store engine parameters when the malfunction occurs. Review this stored information in order to see the specific running conditions that caused the malfunction.
- Freeze Frame/Failure Records can also aid in locating an intermittent condition. Review and capture the information in the Freeze Frame/Failure Record associated with the intermittent DTC being diagnosed. Drive the vehicle within the conditions that were present when the DTC originally set.
- Use the Plot Function on the scan tool to plot selected data parameters. Review this stored information to aid in locating an intermittent condition. Refer to the scan tool Users Guide for more information.
| IMPORTANT | If the intermittent condition exists as a start and then stall, test for DTCs relating to the vehicle theft deterrent system. Test for improper installation of electrical options such as lights, cellular phones, etc. |
Any of the following may cause an intermittent MIL with no stored DTC
- The ignition coils are shorted to a ground or arcing at the ignition wires or the spark plugs.
- The PCM grounds are loose or dirty. Refer to «Engine Controls Schematics»(ref-238195-S26838414512006072400000) .
- The ignition control (IC) wires are 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.
- There is an open diode across the A/C compressor clutch or any other open diodes.
Use the following tables when diagnosing a symptom complaint
- «Testing for Intermittent Conditions and Poor Connections»(ref-238178-S33329058682006072400000)
- «Hard Start»(ref-238263-S36863568832006072400000)
- «Surges/Chuggles»(ref-238263-S37537583732006072400000)
- «Lack of Power, Sluggishness, or Sponginess»(ref-238263-S39664776932006072400000)
- «Detonation/Spark Knock»(ref-238263-S19395766382006072400000)
- «Hesitation, Sag, Stumble»(ref-238263-S20683994892006072400000)
- «Cuts Out, Misses»(ref-238263-S23549467592006072400000)
- «Poor Fuel Economy»(ref-238263-S03933229242006072400000)
- «Poor Fuel Fill Quality»(ref-238263-S08048623182006072400000)
- «Rough, Unstable, or Incorrect Idle and Stalling»(ref-238263-S18690228612006072400000)
- «Dieseling, Run-On»(ref-238263-S27090738982006072400000)
- «Backfire»(ref-238263-S37335816542006072400000)
Hard Start
| Inspection/Test | Action |
|---|
| DEFINITION: Engine cranks OK, but does not start for a long time. Does eventually run, or may start but immediately dies. |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems, and Engine Controls Schematics . Search for bulletins. |
| Sensor/System | Verify that the engine coolant temperature (ECT) sensor is not shifted in value. Connect a scan tool. Compare the engine coolant temperature to 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, measure the resistance of the ECT sensor. Refer to Temperature vs Resistance for resistance specifications. Inspect the mass air flow (MAF) sensor installation. A MAF sensor that is incorrectly installed may cause a hard start. Important: The embossed arrows on the MAF sensor indicate the direction of the intake air flow. The arrows must point toward the engine. Install the MAF in the proper direction. Refer to Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor Replacement . Inspect the camshaft position (CMP) sensor for proper mounting and/or a bad connection. An extended crank occurs if the PCM does not receive a CMP signal. |
| Fuel System | Inspect the fuel pump relay operation. The fuel pump should turn ON for 2 seconds when you turn ON the ignition. Refer to Fuel Pump Electrical Circuit Diagnosis . A faulty in-tank fuel pump check valve allows the fuel in the lines to drain back to the tank after the engine stops. Refer to Fuel System Diagnosis . Verify that both fuel injector fuses are not open. An open fuel injector fuse causes four injectors and four ignition coils not to operate. Inspect the injector circuits and the ignition coil circuits for an intermittent short to ground. Replace the fuse. Refer to Circuit Testing in Wiring Systems. Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . |
| Ignition System | Verify that both fuel injector fuses are not open. An open fuel injector fuse causes four ignition coils and four fuel injectors not to operate. Inspect the ignition coil circuits and the fuel injector circuits for an intermittent short to ground. Refer to Circuit Testing in Wiring Systems. Replace the fuse. Inspect for proper ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . Determine the cause of the conditions before replacing the spark plugs. Inspect for bare or shorted ignition wires. Refer to Spark Plug Wire Inspection . Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis . |
| Engine Mechanical | Inspect for the following conditions: Excessive oil in combustion chamber or leaking valve seals - Refer to Oil Consumption Diagnosis in Engine Mechanical. Low cylinder compression - Refer to Engine Compression Test in Engine Mechanical. Combustion chambers for excessive carbon buildup-Clean the chambers using top engine cleaner. Follow the instructions on the can. Incorrect basic or worn engine parts-Inspect the following: Cylinder heads Camshaft Pistons, etc. Refer to Engine Mechanical. |
Surges/Chuggles
| Inspection/Tests | Action |
|---|
| DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position. |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Verify the driver understands the operation of the transmission torque converter clutch (TCC) and A/C compressor operation as explained in the owners manual. Inform the customer how the TCC and the A/C clutch operates. |
| Sensor/System | NOTE: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in Cautions and Notices. Inspect the heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions. If they do not, inspect 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 delivered to the engine causing a severe driveability problem. Inspect the mass air flow (MAF) sensor connections. Repair or replace damaged terminals. Refer to Connector Repairs in Wiring Systems. |
| Fuel System | Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Verify that each injector harness is connected to the correct injector or cylinder. Relocate injector harnesses as necessary. Inspect for the following that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector Engine oil contaminated by fuel An EVAP canister purge condition Incorrect fuel pressure - Refer to Fuel System Diagnosis . Leaking fuel injectors - Refer to Fuel System Diagnosis . An inaccurate mass air flow (MAF) sensor Blockage on the inlet screen of the MAF sensor - Refer to Manifold Absolute Pressure (MAP) Sensor Replacement . Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted - Refer Intake Air Resonator Replacement . An air filter that is dirty or restricted - Refer to Air Cleaner Element Replacement . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine - Refer to Exhaust Leakage in Engine Exhaust. Vacuum leaks Incorrect fuel pressure - Refer to Fuel System Diagnosis . Restricted fuel injectors - Refer to Fuel System Diagnosis . An inaccurate MAF sensor Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Vacuum hoses that are split, kinked, or improperly connected |
| Ignition System | Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water. Test for proper ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap will cause a driveability problem. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Monitor the Misfire Current Counters while driving the vehicle within the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 . Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis . |
| Engine Mechanical | Verify that the engine coolant temperature (ECT) 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 Engine Overheating in Engine Cooling for diagnosis. |
| Additional Inspections | Visually and physically inspect vacuum hoses for splits, kinks, and proper connections and routing as shown on the Vehicle Emission Control Information label. Inspect the transmission torque converter clutch (TCC) operation. A TCC applying too soon can cause the engine to spark knock. Refer to Diagnostic Starting Point - Automatic Transmission in Automatic Transmission 4L60-E/4L65-E. |
| NOTE |
|---|
| Refer to Silicon Contamination of Heated Oxygen Sensors Notice in Cautions and Notices. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
Lack of Power, Sluggishness, or Sponginess
| Inspection/Tests | Action |
|---|
| DEFINITION: Engine delivers less than expected power. Little or no increase in speed when the accelerator pedal is pushed down part way. |
| Preliminary Inspections | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Remove the air filter element and inspect for dirt or for restrictions. Refer to Air Cleaner Element Replacement and replace as necessary. |
| Fuel System | Inspect both injector fuses for being open. An open injector fuse causes four ignition coils and four injectors not to operate. Replace the fuse. Inspect the ignition coil circuits and the injector circuits for an intermittent short to ground. Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Inspect the fuel injectors. Refer to Fuel Injector Coil Test . Inspect for the following that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector Engine oil contaminated by fuel An EVAP canister purge condition Incorrect fuel pressure - Refer to Fuel System Diagnosis . Leaking fuel injectors - Refer to Fuel System Diagnosis . An inaccurate mass air flow (MAF) sensor Blockage on the inlet screen of the MAF sensor - Refer to Manifold Absolute Pressure (MAP) Sensor Replacement . Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted - Refer Intake Air Resonator Replacement . An air filter that is dirty or restricted - Refer to Air Cleaner Element Replacement . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine - Refer to Exhaust Leakage in Engine Exhaust. Vacuum leaks Incorrect fuel pressure - Refer to Fuel System Diagnosis . Restricted fuel injectors - Refer to Fuel System Diagnosis . An inaccurate MAF sensor Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Vacuum hoses that are split, kinked, or improperly connected |
| Sensor/System | Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Knock Sensor (KS) System Description . |
| Ignition System | Verify that both fuel injector fuses are not open. An open fuel injector fuse causes four ignition coils and four fuel injectors not to operate. Inspect the ignition coil circuit and the injector circuits for an intermittent short to ground. Refer to Circuit Testing in Wiring Systems. Replace the fuse. Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as water is applied. Inspect for proper ignition voltage output with the J 26792 Spark Tester. Remove the spark plugs and inspect for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap will cause a driveability problem. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Monitor the Misfire Current Counters while driving the vehicle within the conditions that the misfire occurred. If a misfiring cylinder can be located with a misfire, use the DTC P0300 table for diagnosis. Refer to DTC P0300 . Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis . |
| Engine Mechanical | Verify that the engine coolant temperature (ECT) 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 will disable the fuel injectors to four cylinders at a time to keep engine temperatures from reaching damaging levels. The system perceives the 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 Engine Overheating in Engine Cooling for diagnosis. Inspect for excessive oil in the combustion chambers and leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical. Test for low cylinder compression. Refer to Engine Compression Test in Engine Mechanical. Inspect for incorrect basic engine parts, including the following: The camshaft - Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical. Refer to Engine Mechanical. |
| Additional Inspections | Inspect the exhaust system for possible restrictions. Perform the following: Inspect the exhaust system for damaged or collapsed pipes. Inspect the mufflers for heat distress or internal failure. Inspect for plugged three-way catalytic converters by comparing the exhaust system back pressure on each side of the engine. Test back pressure by removing the secondary air injection (AIR) check valves near the exhaust manifolds. Refer to Restricted Exhaust in Engine Exhaust. Inspect the transmission torque converter clutch (TCC) for proper operation. Refer to Diagnostic Starting Point - Automatic Transmission in Automatic Transmission-4L60-E/4L65-E. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
Lack of Power, Sluggish or Spongy
Detonation/Spark Knock
| Inspection/Tests | Action |
|---|
| DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening. |
| Preliminary Inspections | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views and Engine Controls Schematics . If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Road test the vehicle and re-evaluate the vehicles performance. |
| Fuel System | Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice . Water intrusion in the heated oxygen sensor (HO2S) connector An exhaust leak between the HO2S and the engine - Refer to Exhaust Leakage . Vacuum leaks Incorrect fuel pressure - Refer to Fuel System Diagnosis . Restricted fuel injectors - Refer to Fuel System Diagnosis . An inaccurate mass air flow (MAF) sensor - Refer to Scan Tool Data List . Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Vacuum hoses that are split, kinked, or improperly connected |
| Ignition System | Verify that the spark plugs are of the proper heat range. Refer to Spark Plug Inspection . |
| Engine Cooling System | Inspect for obvious overheating conditions: Low engine coolant - Refer to Loss of Coolant for the type and amount of engine coolant to be used. Restricted air flow to the radiator or restricted coolant flow through the radiator Inoperative cooling fan - Refer to Cooling Fan Inoperative . |
| Engine Mechanical | Inspect for the following engine mechanical conditions: Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis . Low cylinder compression - Refer to Engine Compression Test . Combustion chambers for excessive carbon buildup-Clean the combustion chamber by using top engine cleaner. Follow the instructions on the can. Inspect for incorrect basic engine parts. Inspect the following: The camshaft - Refer to Camshaft and Bearings Cleaning and Inspection . The cylinder heads - Refer to Cylinder Head Cleaning and Inspection . The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection . Refer to Symptoms - Engine Mechanical . |
| Additional Inspections | Inspect the park/neutral position (PNP) switch operation. Refer to Range Selector Displays Incorrect Range for the 4L60-E/4L65-E transmission or Range Selector Displays Incorrect Range for the 4L80-E/4L85-E engine. Inspect the transmission torque converter clutch (TCC) operation. The TCC applying too soon can cause the engine to spark knock. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice . |
Hesitation, Sag, Stumble
| Inspection/Tests | Action |
|---|
| DEFINITION: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually more pronounced when first trying to make the vehicle move, as from a stop. May cause the engine to stall if severe enough. |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Ground Distribution Schematics in Wiring Systems. |
| Sensor/System | Inspect the manifold absolute pressure (MAP) sensor operation. |
| Fuel System | Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Verify that both fuel injector fuses are not open. An open fuel injector fuse causes 4 ignition coils and 4 fuel injectors not to operate. Inspect the ignition coil circuits and the fuel injector circuits for an intermittent short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Replace the fuse. Inspect the fuel injectors. Refer to Fuel Injector Coil Test . Inspect for the following that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the heated oxygen sensor (HO2S) connector Engine oil contaminated by fuel An evaporative emission (EVAP) canister purge condition Incorrect fuel pressure - Refer to Fuel System Diagnosis . Leaking fuel injectors - Refer to Fuel System Diagnosis . An inaccurate mass air flow (MAF) sensor - Refer to Scan Tool Data List . Blockage on the inlet screen of the MAF sensor - Refer to Manifold Absolute Pressure (MAP) Sensor Replacement . Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted - Refer Intake Air Resonator Replacement . An air filter that is dirty or restricted - Refer to Air Cleaner Element Replacement . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine - Refer to Exhaust Leakage in Engine Exhaust. Vacuum leaks Incorrect fuel pressure - Refer to Fuel System Diagnosis . Restricted fuel injectors - Refer to Fuel System Diagnosis . An inaccurate MAF sensor - Refer to Scan Tool Data List . Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Vacuum hoses that are split, kinked, or improperly connected |
| Ignition System | Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. Test for proper ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis for the procedure. Remove the spark plugs and inspect for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool. Refer to Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 . Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis . |
| Engine Cooling System | Inspect the engine thermostat for proper operation and for proper heat range. Refer to Thermostat Diagnosis in Engine Cooling. |
| Additional Inspections | Inspect the generator output voltage. Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
Cuts Out, Misses
| Inspections | Action |
|---|
| DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. This condition is not normally felt above 1,500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or low speed. |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Remove the air filter element and inspect for dirt and for restrictions. Refer to Air Cleaner Element Replacement . Replace as necessary. |
| Fuel System | Test the fuel injectors. Refer to Fuel Injector Coil Test . Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Inspect for the following that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the heated oxygen sensor (HO2S) connector Engine oil contaminated by fuel An evaporative emission (EVAP) canister purge condition Incorrect fuel pressure - Refer to Fuel System Diagnosis . Leaking fuel injectors - Refer to Fuel System Diagnosis . An inaccurate mass air flow (MAF) sensor - Refer to Scan Tool Data List . Blockage on the inlet screen of the MAF sensor Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted - Refer Intake Air Resonator Replacement . An air filter that is dirty or restricted - Refer to Air Cleaner Element Replacement . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine - Refer to Exhaust Leakage in Engine Exhaust. Vacuum leaks Incorrect fuel pressure - Refer to Fuel System Diagnosis . Restricted fuel injectors - Refer to Fuel System Diagnosis . An inaccurate MAF sensor - Refer to Scan Tool Data List . Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Vacuum hoses that are split, kinked, or improperly connected |
| Sensor/System | Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. |
| Ignition System | Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. Test for proper ignition voltage output with the J 26792 Spark Tester. Remove the spark plugs and inspect for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap may cause a driveability problem. Refer to Spark Plug Inspection . Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Visually and physically inspect the secondary ignition for the following conditions: The ignition wires arcing to ground The ignition wires for proper engagement to spark plug The ignition coils for cracks or carbon tracking Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 . |
| Engine Mechanical | Inspect engine mechanical for the following conditions: Inspect compression - Refer to Engine Compression Test in Engine Mechanical. Sticking or leaking valves Worn camshaft lobes Valve timing Bent push rods Worn rocker arms Broken valve springs Excessive oil in combustion chamber - Refer to Oil Consumption Diagnosis in Engine Mechanical. For incorrect basic engine parts inspect the following: The camshaft - Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical. Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnostic procedures. |
| Additional Inspections | Inspect the exhaust system for possible restrictions. Inspect for the following: Inspect the exhaust system for damaged or collapsed pipes. Inspect the mufflers for heat distress or possible internal failure. Inspect for possible plugged catalytic converters by comparing the exhaust system back pressure on each side of engine. Refer to Restricted Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the reference circuit can cause an engine misfire condition. A sudden increase in indicated RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components near ignition control circuits if a condition exists. Inspect the intake manifold and the exhaust manifold passages for casting flash. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
Poor Fuel Economy
| Inspections | Action |
|---|
| DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, fuel economy is noticeably lower than the economy was on this vehicle at one time, as previously shown by an actual road test. |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Inspect the owners driving habits for the following conditions: The A/C ON or the Defroster mode ON full time The tires at the correct pressure Excessively heavy loads being carried The acceleration rate is too much, too often Remove the air filter element and inspect for dirt or for restrictions. Refer to Air Cleaner Element Replacement . Replace as necessary. |
| Fuel System | Inspect the type, quality, and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Test the fuel injectors. Refer to Fuel Injector Coil Test . Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Inspect that each fuel injector harness is connected to the correct injector and cylinder. Relocate the injector harnesses as necessary. Inspect for foreign material accumulation in the throttle bore, coking on the throttle valve, or on the throttle shaft. Inspect for the following that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the heated oxygen sensor (HO2S) connector Engine oil contaminated by fuel An evaporative emission (EVAP) canister purge condition Incorrect fuel pressure - Refer to Fuel System Diagnosis . Leaking fuel injectors - Refer to Fuel System Diagnosis . An inaccurate mass air flow (MAF) sensor - Refer to Scan Tool Data List . Blockage on the inlet screen of the MAF sensor - Refer to Manifold Absolute Pressure (MAP) Sensor Replacement . Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted - Refer Intake Air Resonator Replacement . An air filter that is dirty or restricted - Refer to Air Cleaner Element Replacement . |
| Sensor/System | Inspect the air intake system and crankcase for air leaks. Inspect the crankcase ventilation system. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical. Inspect for an inaccurate speedometer. Refer to Instrument Panel Cluster (IPC) Gages Inoperative in Instrument Panel, Gages, and Console. Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Knock Sensor (KS) System Description . |
| Ignition System | Inspect for proper ignition voltage output with the J 26792 Spark Tester. Remove the spark plugs and inspect for the following conditions: Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap will cause a driveability condition. Refer to Spark Plug Inspection . Gap the spark plugs using a wire gage gap tool Refer to Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Refer to Spark Plug Inspection . Visually and physically inspect the secondary ignition for the following conditions: Ignition wires arcing to ground Ignition wires for proper routing Soaking 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. Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis . |
| Engine Cooling System | Inspect the engine coolant level for being low. Refer to Loss of Coolant in Engine Cooling. Inspect the engine thermostat for proper operation and for the correct heat range. Refer to Thermostat Diagnosis in Engine Cooling. |
| Engine Mechanical | Inspect engine mechanical for the following conditions: Compression - Refer to Engine Compression Test in Engine Mechanical. 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. Refer to Oil Consumption Diagnosis in Engine Mechanical. For incorrect basic engine parts inspect for the following: The camshaft - Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical. Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnostic procedures. |
| Additional Inspections | Visually and physically inspect the vacuum hoses for splits, kinks, and proper connections and routing as shown on Vehicle Emission Control Information label. Inspect the transmission torque converter clutch (TCC) operation. The scan tool should indicate a RPM drop, when the system commands the TCC ON. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission - 4L60-E/4L65-E. Inspect the exhaust system for a possible restriction. Inspect for the following: The exhaust system for damaged or collapsed pipes The mufflers for heat distress or possible internal failure For possible plugged three-way catalytic converters by comparing the exhaust system back pressure on each side of the engine-Inspect the back pressure by removing the secondary air injection (AIR) check valves near the exhaust manifolds. Refer to Restricted Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components, near ignition control circuits, if a condition exists. Inspect the park neutral position (PNP) switch circuit. Refer to Range Selector Displays Incorrect Range in Automatic Transmission - 4L60-E/4L65-E or Range Selector Displays Incorrect Range in Automatic Transmission - 4L80-E/4L85-E. Inspect the brake system for dragging or improper operation. Refer to Brake Caliper Inspection in Disc Brakes. Verify that the vehicle operator does not drive with a foot on the brake pedal. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
Poor Fuel Fill Quality
| Problem | Causes |
|---|
| DEFINITION: Difficulty when refueling the vehicle. |
| Difficult to fill | If the vehicle is equipped with dual fuel tanks and a single filler neck the flow of the fuel into the tanks may exceed the ability of the system to compensate, the fill nozzle will automatically shut off. The system will require 10-20 seconds to equalize pressure before filling can resume. Refer to Fuel System Description . The check valve is stuck closed. The fill limiter vent valve is stuck closed. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The evaporative emission (EVAP) canister is restricted. Refer to Evaporative Emission (EVAP) Canister Replacement (Pickup) or Evaporative Emission (EVAP) Canister Replacement (Cab/Chassis) . The EVAP canister vent solenoid is stuck closed. Refer to Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement (Pickup) Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement (Cab/Chassis) . Restricted EVAP pipes - Refer to Evaporative Emission (EVAP) Hoses/Pipes Replacement - Canister/Fuel Tank . High reid vapor pressure High fuel temperature The fuel filler hose/pipe is pinched, kinked or blocked. Refer to Filler Tube Replacement (Pickup) , Filler Tube Replacement (Cab/Chassis - Front) or Filler Tube Replacement (Cab/Chassis - Rear) . The fuel feed hose, or crossover hose, is pinched, kinked or blocked. Refer to Fuel Rail Assembly Replacement . The ignition switch is ON. |
| Over fill | The pressure relief valve in the fill limiter vent valve is stuck open. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The pressure relief valve in the fill limiter vent is valve leaking. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The fill limiter vent valve is stuck open. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The fill limiter vent valve is leaking. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . |
| Premature shut-off of the fuel dispensing nozzle | The fill limiter vent valve is stuck closed. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The EVAP canister is restricted. Refer to Evaporative Emission (EVAP) Canister Replacement (Pickup) or Evaporative Emission (EVAP) Canister Replacement (Cab/Chassis) . The EVAP canister vent solenoid is stuck closed. Refer to Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement (Pickup) Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement (Cab/Chassis) . Restricted EVAP pipes - Refer to Evaporative Emission (EVAP) Hoses/Pipes Replacement - Canister/Fuel Tank . High Reid vapor pressure High fuel temperature The fuel filler hose/pipe is pinched, kinked or blocked. Refer to Filler Tube Replacement (Pickup) or Filler Tube Replacement (Cab/Chassis - Front) or Filler Tube Replacement (Cab/Chassis - Rear) . The fuel feed hose, or crossover hose, is pinched, kinked or blocked. Refer to Fuel Rail Assembly Replacement . The ignition switch is ON. |
| Fuel spit back | The check valve is stuck open. The check valve is stuck closed. The check valve is leaking. High Reid vapor pressure High fuel temperature |
| Liquid fuel in the EVAP canister | The fill limiter vent valve is stuck open. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The fill limiter vent valve is leaking. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . |
| Liquid fuel leak | The pressure relief valve in the fill limiter vent valve is stuck open. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The pressure relief valve in the fill limiter vent valve is leaking. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The fuel filler hose is loose or torn. Refer to Filler Tube Replacement (Pickup) , Filler Tube Replacement (Cab/Chassis - Front) or Filler Tube Replacement (Cab/Chassis - Rear) . The fuel feed hose, or crossover hose, is loose or torn. Refer to Fuel Rail Assembly Replacement . The fill limiter vent valve is stuck open. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . |
| Fuel odor | The pressure relief valve in the fill limiter vent valve is stuck open. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The pressure relief valve in the fill limiter vent valve is leaking. Refer to Fuel Tank Replacement (Pickup) , Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) . The EVAP canister is saturated. Refer to Evaporative Emission (EVAP) Canister Replacement (Pickup) or Evaporative Emission (EVAP) Canister Replacement (Cab/Chassis) . |
Rough, Unstable, or Incorrect Idle and Stalling
| Inspections | Action |
|---|
| 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 Inspections | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Remove and inspect the air filter element for dirt or for restrictions. Refer to Air Cleaner Element Replacement . Replace as necessary. |
| Fuel System | Inspect the fuel injectors. Refer to Fuel Injector Coil Test . Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Inspect that each fuel injector harness is connected to the correct injector/cylinder. Relocate fuel injector harnesses as necessary. Inspect for the following that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the heated oxygen sensor (HO2S) connector Engine oil contaminated by fuel An evaporative emission (EVAP) canister purge condition Incorrect fuel pressure - Refer to Fuel System Diagnosis . Leaking fuel injectors - Refer to Fuel System Diagnosis . An inaccurate mass air flow (MAF) sensor Blockage on the inlet screen of the MAF sensor - Refer to Manifold Absolute Pressure (MAP) Sensor Replacement . Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted - Refer Intake Air Resonator Replacement . An air filter that is dirty or restricted - Refer to Air Cleaner Element Replacement . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine - Refer to Exhaust Leakage in Engine Exhaust. Vacuum leaks Incorrect fuel pressure - Refer to Fuel System Diagnosis . Restricted fuel injectors - Refer to Fuel System Diagnosis . An inaccurate MAF sensor Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Vacuum hoses that are split, kinked, or improperly connected |
| Sensor/System | Inspect the crankcase ventilation valve for proper operation. Place a finger over the inlet hole of the valve end several times. The valve should snap back. If not, replace the valve. Refer to Crankcase Ventilation System Description in Engine Mechanical. Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. |
| Ignition System | Inspect for proper ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis for procedure. Remove spark plugs and check for the following conditions: Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap will cause a driveability problem. Refer to Spark Plug Inspection . Gap the spark plugs using a wire gage gap tool. Refer to Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Visually and physically inspect secondary ignition for the following conditions: Ignition wires arcing to ground Ignition wires for proper routing Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 . Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis . |
| Engine Mechanical | Inspect engine mechanical for the following conditions: Compression - Refer to Engine Compression Test in Engine Mechanical. Sticking or leaking valves Worn camshaft lobes Valve timing Bent push rods Worn rocker arms Broken valve springs Excessive oil in combustion chamber or leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical. For incorrect basic engine parts. Inspect the following: The camshaft - Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical. Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnosis procedures. |
| Additional Inspections | Inspect the exhaust system for possible restrictions. Inspect for the following: Inspect the exhaust system for damaged or collapsed pipes. Inspect the mufflers for heat distress or possible internal failure. Inspect for possible plugged three-way catalytic converters by comparing exhaust system back pressure on each side of engine. Inspect the back pressure by removing secondary air injection (AIR) check valves near exhaust manifolds. Refer to Restricted Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change indicates that EMI is present. If a problem exists, inspect routing of secondary ignition wires or high voltage components near the ignition control circuits. Inspect the park neutral position (PNP) switch circuit. Refer to Park/Neutral Position Switch Adjustment in Automatic Transmission 4L60-E/4L65-E. Inspect for faulty motor mounts. Refer to Engine Mount Inspection in Engine Mechanical. Inspect the intake manifold and the exhaust manifold passages for casting flash. Inspect for an exhaust gas recirculation (EGR) valve stuck open or EGR pintle not seating properly. Inspect EGR valve gasket for leaks. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
| NOTE |
|---|
| Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. |
Rough, Unstable, or Incorrect Idle and Stalling
Dieseling, Run-On
| Inspections | Action |
|---|
| DEFINITION: Engine continues to run after key is turned OFF, but runs very rough. If the engine runs smooth, inspect the ignition switch and the ignition switch adjustment. |
| Preliminary Inspections | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . |
| Fuel System | Inspect the fuel injectors for a leaking condition. Refer to Fuel System Diagnosis for the proper procedure. |
Backfire
| Inspections | Actions |
|---|
| DEFINITION: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise. |
| Preliminary Inspections | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls. Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . |
| Fuel System | Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Inspect the fuel injectors. Refer to Fuel Injector Coil Test . Verify that each injector harness is connected to the correct injector or cylinder. Relocate injector harnesses as necessary. |
| Sensor/System | Inspect the secondary air injection (AIR) system. Inspect the air intake system and crankcase for air leaks. Inspect the crankcase ventilation valve for proper operation. Place a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace the valve. Refer to Crankcase Ventilation System Description in Engine Mechanical. Inspect for an inaccurate speedometer. Refer to Instrument Panel Cluster (IPC) Gages Inoperative in Instrument Panel, Gages, and Console. Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Knock Sensor (KS) System Description . |
| Ignition System | Inspect for proper ignition voltage output with the J 26792 Spark Tester. Remove spark plugs and inspect for the following conditions: Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap will cause a driveability condition. Refer to Spark Plug Inspection . Gap the spark plugs using a wire gage gap tool. Refer to Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Refer to Spark Plug Inspection for diagnosis. Visually and physically inspect secondary ignition for the following conditions: Ignition wires arcing to ground Ignition coils arcing to ground Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 . Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis . |
| Engine Cooling System | Inspect the engine coolant level for being low. Refer to Loss of Coolant in Engine Cooling. Inspect the engine thermostat for proper operation and for the correct heat range. Refer to Thermostat Diagnosis in Engine Cooling. |
| Engine Mechanical | Inspect engine mechanical for the following conditions: Compression - Refer to Engine Compression Test in Engine Mechanical. Sticking or leaking valves Worn camshaft lobes Valve timing Bent push rods Worn rocker arms Broken valve springs Excessive oil in combustion chamber or leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical. For incorrect basic engine parts. Inspect the following: The camshaft - Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical. Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnosis procedures. |
| Additional Inspections | Visually and physically inspect the vacuum hoses for splits, kinks, and proper connections and routing as shown on the Vehicle Emission Control Information label. Inspect the intake manifold and the exhaust manifold passages for casting flash. Inspect the transmission torque converter clutch (TCC) operation. The scan tool should indicate an RPM drop when the TCC is commanded ON. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission - 4L60-E/4L65-E or Torque Converter Diagnosis Procedure in Automatic Transmission - 4L80-E/4L85-E. Inspect the exhaust system for possible restrictions. Inspect the following: The exhaust system for damaged or collapsed pipes The mufflers for heat distress or possible internal failure Possible plugged 3-way catalytic converters by comparing exhaust system back pressure on each side of engine-Inspect back pressure by removing AIR check valves near exhaust manifolds. Refer to Restricted Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change may indicate that EMI is present. If a condition exists, inspect for high voltage components near the ignition control circuits. Inspect the park/neutral position (PNP) switch operation. Refer to Park/Neutral Position Switch Adjustment in Automatic Transmission - 4L60-E/4L65-E. Inspect for faulty motor mounts. Refer to Engine Mount Inspection in Engine Mechanical. Inspect the intake manifold and the exhaust manifold passages for casting flash. |
Conditions for Updating the I/M System Status
Each system monitor requires at least one, and sometimes several diagnostic tests. The result of each test is reported by a diagnostic trouble code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have Run and Passed, or when any one of the DTCs comprising the monitor has illuminated the malfunction indicator lamp (MIL). Once the system monitor is complete, the I/M System Status display will indicate YES in the Completed column.
For example, when the HO2S Heater Status indicates YES, either all of the oxygen sensor heater tests have passed or one of the tests has illuminated the MIL. If the vehicle has four heated oxygen sensors, either all four heater circuit tests have passed or one of the heater circuit tests has illuminated the MIL. The I/M System Status will indicate NO under the Completed column when any of the required tests for that system have not run. The following is a list of conditions that would set the I/M System Status indicator to NO
- The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
- The battery has been disconnected or discharged below operating voltage.
- The control module power or ground has been interrupted.
- The control module has been reprogrammed.
- The control module DTCs have been cleared.
Monitored Emission Control Systems
The OBD II System monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with secondary air injection (AIR) or exhaust gas recirculation (EGR). The OBD II regulations require monitoring of the following
- The air conditioning system
- The catalytic converter efficiency
- Comprehensive component monitoring-Emission related inputs and outputs
- The evaporative emissions (EVAP) system
- The EGR System
- The fuel delivery system
- Heated catalyst monitoring
- Misfire monitoring
- The oxygen sensor system (O2S or HO2S)
- The oxygen sensor heater system (HO2S heater)
- The AIR system
For the specific DTCs required for each system, refer to Inspection/Maintenance (I/M) System DTC Table . Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list. These tests run continuously and do not require an I/M System Status indicator.
| Step | Action | Value(s) | Yes | No |
|---|
| 1 | Perform the Diagnostic System Check - Vehicle in Vehicle DTC Information. IMPORTANT: Many DTC related repairs will instruct the technician to clear the DTC information. This procedure will reset ALL of the I/M System Status indicators to NO, and require performing the I/M Complete System Set Procedure. Repair any DTCs or driveability concerns that would prevent the I/M System Status tests from completing. Did you find and repair a DTC or driveability concern? | | Go to Step 3 | Go to Step 2 |
| 2 | Review any service bulletins for software updates that may prevent inspection/maintenance (I/M) readiness. Perform any reprogramming or repairs indicated by the service bulletins. Was a reprogramming or repair service required? | | Go to Inspection/Maintenance (I/M) Complete System Set Procedure | Go to Step 3 |
| 3 | Observe the I/M System Status display with a scan tool. Is more than one test indicating a NO status? | | Go to Inspection/Maintenance (I/M) Complete System Set Procedure | Go to the I/M System Set Procedure for the indicated systems that have not updated |
| IMPORTANT |
|---|
| Many DTC related repairs will instruct the technician to clear the DTC information. This procedure will reset ALL of the I/M System Status indicators to NO, and require performing the I/M Complete System Set Procedure. |
Inspection/Maintenance (I/M) System Check
I/M Data List
To determine if the I/M readiness diagnostic tests can be run this ignition cycle, use a scan tool to observe the I/M monitor enabled parameters in the I/M Data List.
Conditions for Meeting a Cold Start
- The ignition voltage between 11.0 and 18.0 volts.
- The barometric pressure (BARO) is more than 75 kPa.
- The start-up engine coolant temperature (ECT) is between 4-30°C (39-86°F).
- The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).
- The difference between the IAT and the ECT is 6°C (10.8°F)
- The ambient air temperature is between 4-30°C (39-86°F).
- Fuel level is between 15 and 85 percent
Circuit/System Verification
Review the I/M System Status indicators with a scan tool. All I/M System Status indicators should report YES.
