Engine Controls - 6.0L - Troubleshooting: Diagnosis Pontiac GTO IV

Important Preliminary Inspections Before Beginning

Before using this section, perform the Diagnostic System Check - Vehicle in Vehicle DTC Information and verify all of the following conditions

1. The engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly. Refer to «Malfunction Indicator Lamp (MIL) Inoperative»(ref-201043-S41742549312005102400000) .
2. Diagnostic trouble codes (DTCs) are not stored.
3. The scan tool data is within the normal operating range. Refer to «Scan Tool Data List»(ref-201057-S31794014152005102400000) .
4. Verify the customer concern and locate the correct symptom table. Inspect the items indicated in that symptom table.
5. Several of the symptom procedures ask for a careful visual/physical inspection. This step is extremely important, and can lead to correcting a condition without further inspections and can save valuable time.
6. If the intermittent condition exists as a start and then stall, inspect for any DTCs related to the theft deterrent system. Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(ref-201037-S01449858442005102400000) in Vehicle DTC Information.
7. Verify the proper installation of any of the following aftermarket accessories: Lights Cellular phone Remote starter system Aftermarket installed alarm
8. Use the following tables when diagnosing a symptom concern: «Poor Fuel Fill Quality»(ref-201043-S17024726072005102400000) «Hard Start»(ref-201043-S08044693202005102400000) «Surges/Chuggles»(ref-201043-S30480258842005102400000) «Lack of Power, Sluggishness, or Sponginess»(ref-201043-S25700340892005102400000) «Detonation/Spark Knock»(ref-201043-S29772218442005102400000) «Hesitation, Sag, Stumble»(ref-201043-S24902615052005102400000) «Cuts Out, Misses»(ref-201043-S09026006442005102400000) «Poor Fuel Economy»(ref-201043-S41821181132005102400000) «Rough, Unstable, or Incorrect Idle and Stalling»(ref-201043-S33548850732005102400000) «Dieseling, Run-On»(ref-201043-S06874981522005102400000) «Backfire»(ref-201043-S14843035692005102400000)
9. If the condition cannot be isolated using the appropriate table, refer to «Testing for Intermittent Conditions and Poor Connections»(ref-201038-S37853796532005102400000) for further diagnosis.

Circuit Description

Ignition voltage is supplied to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

Battery positive voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit.

Diagnostic Aids

If the problem is intermittent, refer to Intermittent Conditions .

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within two seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within two seconds if ignition reference pulses cease to be detected and the ignition remains ON.

The control module enables the appropriate fuel injector on the intake stroke for each cylinder. Ignition voltage is supplied directly to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low will affect engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

1. Monitoring the misfire current counters, or misfire graph, may help isolate the fuel injector that is causing the condition.
2. Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.
3. Perform the fuel injector coil test within the conditions of the customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.

Fuel Injector Coil Test

1. Operate the vehicle under the condition of the customers concern. Under high temperature conditions fuel vapors may increase to the point of EVAP canister vapor saturation. Fuel vapors would then be released into the atmosphere. Once the engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
2. Movement of the EVAP pipes or fuel pipes may help find an intermittent condition.
3. If the fuel level is low, a leak may not be evident.

Alcohol in Fuel Testing Procedure

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. The sample should be bright and clear. If alcohol contamination is suspected then use the following procedure to test the fuel quality.

1. Using a 100 ml specified cylinder with 1 ml graduation marks, fill the cylinder with fuel to the 90 ml mark.
2. Add 10 ml of water in order to bring the total fluid volume to 100 ml and install a stopper.
3. Shake the cylinder vigorously for 10-15 seconds.
4. Carefully loosen the stopper in order to release the pressure.
5. Re-install the stopper and shake the cylinder vigorously again for 10-15 seconds.
6. Put the cylinder on a level surface for approximately 5 minutes in order to allow adequate liquid separation.

If alcohol is present in the fuel, the volume of the lower layer, which would now contain both alcohol and water, will be more than 10 mL. For example, if the volume of the lower layer is increased to 15 ml, this indicates at least 5 percent alcohol in the fuel. The actual amount of alcohol may be somewhat more because this procedure does not extract all of the alcohol from the fuel.

Particulate Contaminants in Fuel Testing Procedure

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. The sample should be bright and clear. If the sample appears cloudy, or contaminated with water, as indicated by a water layer at the bottom of the sample, use the following procedure to diagnose the fuel.

1. Using an approved fuel container, draw approximately 0.5 liter of fuel.
2. Place the cylinder on a level surface for approximately 5 minutes in order to allow settling of the particulate contamination.

Particulate contamination will show up in various shapes and colors. Sand will typically be identified by a white or light brown crystals. Rubber will appear as black and irregular particles. If particles are found clean the entire fuel system thoroughly. Refer to Fuel System Cleaning .

Test Procedure

1. Test the fuel composition using J 44175 Fuel Composition Tester and J 44175-3 Instruction Manual. See «Special Tools»(ref-201043-S19962986522005102400000) .
2. If water appears in the fuel sample, perform the following steps: Clean the fuel system. Refer to «Fuel System Cleaning»(ref-201043-S15427851942005102400000) . Replace the fuel filter if the vehicle is equipped with a serviceable fuel filter.
3. Subtract 50 from the reading on the DMM in order to obtain the percentage of alcohol in the fuel sample. Refer to the examples in the Fuel Composition Test Examples table.
4. If the fuel sample contains more than 15 percent ethanol, add fresh, regular gasoline to the vehicle's fuel tank.
5. Test the fuel composition.
6. If testing shows the ethanol percentage is still more than 15 percent, replace the fuel in the vehicle. Refer to «Fuel System Cleaning»(ref-201043-S15427851942005102400000) .

Fuel Composition Test Examples

The electronic ignition system uses an individual ignition coil for each cylinder. The engine control module (ECM) controls the ignition operation through eight individual ignition control (IC) circuits. Each bank of four ignition coils is connected to the ECM, power, or ground by the following circuits

1. A low reference circuit
2. A chassis ground circuit
3. An ignition 1 voltage circuit
4. The appropriate IC circuit

The ECM triggers an ignition coil by grounding the appropriate IC circuit using information from the crankshaft position (CKP) and camshaft position (CMP) sensors.

For an intermittent condition, refer to Intermittent Conditions .

Conditions for Running

Cold Start

1. The barometric pressure (BARO) is more than 75 kPa.
2. The engine coolant temperature (ECT) is between 4-30°C (39-86°F).
3. The intake air temperature (IAT) is between 4-30°C (39-86°F).
4. The difference between the IAT and the ECT is 8°C (14°F) or less.
5. The battery voltage is between 10-18 volts.
6. The fuel level is between 15-85 percent.

Rough road conditions may prevent some of the tests from running. Extreme high or low ambient temperatures may prevent tests such as for the heated oxygen sensor (HO2S) heater and the evaporative emission (EVAP) system from initiating. If a step is interrupted before completion, perform the remaining portion of the set procedures. Any portion of the set procedure that requires the engine at operating temperature may be repeated. This allows most of the diagnostics to run and the remaining tests can be performed using the individual System Set Procedures.

The scan tool can be used in order to monitor each of the I/M System Status indicators during the I/M Complete System Set Procedure. When all of the indicators for a test step have updated to YES, testing can move on to the next step even if the remaining portion of the test is not complete. For example, step 3 is designed to run the EVAP, AIR, and HO2S tests. The procedure instructs the technician to operate the vehicle in the enable conditions for 6 minutes. If all 3 tests have updated to YES within 4 minutes, you do not need to continue with the enable conditions and testing can advance to the next step.

Inspection/Maintenance (I/M) System DTC Table

Inspection/Maintenance (I/M) System DTC Table

1. The barometric pressure is more than 70 kPa.
2. The engine coolant temperature (ECT) is between 70-125.5°C (158-258°F).
3. The battery voltage is more than 11 volts.
4. The fuel alcohol content is less than 87 percent.

The control module runs a maximum of 6 catalyst tests per trip until the Catalyst System Status updates to YES. If the status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Catalyst System Set Procedure

Scan Tool Service Bay Test Equipped Vehicles

1. Stored engine controller DTCs have been cleared.
2. The battery voltage is between 10-18 volts.
3. The engine coolant temperature (ECT) is less than 70°C (158°F) at start-up.
4. The fuel level is 15-85 percent.
5. The vehicle must be in Park or Neutral during the test.
6. The test can take up to 17 minutes to complete and set the I/M system status, depending on the fuel level and the fuel volatility.

Non Scan Tool Service Bay Test Equipped Vehicles

1. DTCs P0442, P0446, P0455, P0496 are not set.
2. The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).
3. The ECT is less than 30°C (86°F).
4. The start-up IAT and ECT are within 8°C (15°F).
5. The barometric pressure (BARO) is more than 74 kPa.
6. The ambient air temperature is between 2-32°C (36-90°F).
7. The engine run time minimum is 10 minutes.
8. The trip drive length is more than 5 kilometers (3.1 miles).
9. The ECT is more than 70°C (158°F).
10. The fuel level is between 15-85 percent.
11. The above conditions must be met a minimum of three times for DTC P0442 System Small Leak Detected to report a pass.

Extreme high or low ambient temperatures may prevent the EVAP system tests from initiating. Performing an inspection prior to running the EVAP Service Bay Test may prevent having to repeat the test. A loose fuel cap may cause a Service Bay Test to abort or fail and prevent the I/M system status from updating. A failed or aborted test will require the vehicle to cool down in order to meet the enable criteria to run another test.

The I/M system status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the I/M system status will update to YES. If a test for a specific system has failed, the I/M system status will update to YES, indicating a determination was made, even if all of the required tests have not run. When a failure occurs, the emission related DTC portion of the I/M system status display will indicate the malfunction indicator lamp (MIL) is requested. The I/M system status also registers the number of DTCs.

Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure

1. The fuel level is more than 10 percent.
2. The engine coolant temperature (ECT) is more than 55°C (131°F).
3. The battery voltage is between 10-18 volts.
4. The fuel alcohol content is less than 90 percent.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Heated Oxygen Sensor/Oxygen Sensor (HO2S/O2S) System Set Procedure

1. The intake air temperature (IAT) is between 30-45°C (22-113°F).
2. The difference between the IAT and the ECT is less than 8°C (14°F).
3. The battery voltage is between 11-18 volts.

The HO2S Heater Tests will normally run within the 2 minutes allotted in the procedure. If there is an indeterminate condition, the test may take up to 8 minutes on some vehicles before a decision of pass or fail is made. If the test does not update to YES, it may have failed or aborted due to the loss of enabling conditions. Extremely high ambient temperatures may prevent the HO2S Heater Test from initiating.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Heated Oxygen Sensor (HO2S) Heater System Set Procedure

Conditions for Running the Test

The following conditions must be met in order to enable the Service Bay Test

1. The battery voltage is between 11-18 volts.
2. The start-up engine coolant temperature (ECT) is less than 70°C (158°F).
3. The fuel level is 15-85 percent.
4. Stored engine controller DTCs have been cleared.
5. The vehicle must be in Park or Neutral during the test.
6. The test can take up to 17 minutes to complete and set the I/M system status, depending on fuel level and fuel volatility.

1. Install a scan tool.
2. With the scan tool, select the Service Bay Test.
3. Follow the instructions on the scan tool.
4. Verify that the EVAP I/M System Status is set to YES.
5. Check DTCs with the scan tool.
6. Continue with the published service manual diagnostic DTC procedure.

Spark Plug Wire Inspection

Spark plug wire integrity is vital for proper engine operation. A thorough inspection will be necessary to accurately identify conditions that may affect engine operation. Inspect for the following conditions

1. Correct routing of the spark plug wires-Incorrect routing may cause cross-firing.
2. Any signs of cracks or splits in the wires.
3. Inspect each boot for the following conditions: Tearing Piercing Arcing Carbon tracking Corroded terminal

If corrosion, carbon tracking or arcing are indicated on a spark plug wire boot or on a terminal, replace the wire and the component connected to the wire.

Spark Plug Inspection

1. Inspect the terminal post (1) for damage. Inspect for a bent or broken terminal post (1). Test for a loose terminal post (1) by twisting and pulling the post. The terminal post (1) should NOT move.
2. Inspect the insulator (2) for flashover or for carbon tracking soot. This condition is caused by the electrical charge traveling across the insulator (2) between the terminal post (1) and ground. Inspect for the following conditions: Inspect the spark plug boot for damage. Inspect the spark plug recess area of the cylinder head for moisture from such oil, from coolant, or from water. A saturated spark plug boot causes arcing to ground.
3. Inspect the insulator (2) for cracks. All or part of the electrical charge may arc through the crack instead of through the electrodes (3, 4).
4. Inspect for evidence of improper arcing. Measure the gap between the center electrode (4) and the side electrode (3) terminals. Refer to «Ignition System Specifications»(ref-201087-S28844541212005102400000) . An excessively wide electrode gap can prevent correct spark plug operation. Inspect for the correct spark plug torque. Refer to «Ignition System Specifications»(ref-201087-S28844541212005102400000) . Insufficient torque can prevent correct spark plug operation. An over-torqued spark plug causes the insulator (2) to crack. Inspect for signs of tracking that occurred near the insulator tip instead of at the center electrode (4). Inspect for a side electrode (3) that is broken or worn. Inspect for a broken, worn, or loose center electrode (4) by shaking the spark plug. A rattling sound indicates internal damage. A loose center electrode (4) reduces the spark intensity. Inspect for bridged electrodes (3, 4). Deposits on the electrodes reduce or eliminate the gap. Inspect for worn or missing platinum pads on the electrodes (3, 4), if equipped. Inspect for excessive fouling.
5. Inspect the spark plug recess area of the cylinder head for debris. Dirty or damaged threads can cause the spark plug not to seat correctly during installation.

Spark Plug Visual Inspection

1. Normal operation-Brown to grayish-tan spark plugs, with small amounts of white powdery deposits are normal combustion by-products from fuels with additives.
2. Carbon-fouled plugs-Dry, fluffy black carbon or soot caused by the following conditions: Rich fuel mixtures Leaking fuel injectors Excessive fuel pressure Restricted air filter element Incorrect combustion Reduced ignition system voltage output Weak coils Worn ignition wires Incorrect spark plug gap Excessive idling or slow speeds during light loads can keep the spark plug temperatures so low that the normal combustion deposits may not burn off.
3. Deposit fouling-Oil, coolant, or additives that include substances such as silicone, evidenced by a very white coating, reduces the spark intensity. Most powdery deposits will not affect spark intensity unless they form into a glazing over the electrode.

Large Leak Test

This tests for large leaks and blockages in the evaporative emission (EVAP) system. The control module will command the EVAP vent solenoid ON, closed, and command the EVAP purge solenoid ON, open, with the engine running, allowing engine vacuum into the EVAP system. The control module monitors the Fuel Tank Pressure (FTP) sensor voltage to verify that the system is able to reach a predetermined level of vacuum within a set amount of time. The control module then commands the EVAP purge solenoid OFF, closed, sealing the system and monitors the vacuum level for decay. If the control module does not detect that the predetermined vacuum level was achieved, or the vacuum decay rate is more than a calibrated level on 2 consecutive tests, a DTC P0455 will set.

Small Leak Test

If the large leak test passes, the control module will test for small leaks by continuing to monitor the Fuel Tank Pressure (FTP) sensor for a change in voltage over a period of time. If the decay rate is more than a calibrated value, the control module will rerun the test. If the test fails again, a DTC P0442 will set.

Canister Vent Restriction Test

If the evaporative emission (EVAP) vent system is restricted, fuel vapors will not be properly purged from the EVAP canister. The control module tests this by commanding the EVAP purge solenoid ON, open; and commanding the EVAP vent solenoid OFF, open; and monitoring the FTP sensor for an increase in vacuum. If vacuum increases more than a calibrated value, DTC P0446 will set.

Purge Solenoid Leak Test

If the evaporative emission (EVAP) purge solenoid does not seal properly, fuel vapors could enter the engine at an undesired time, causing driveability concerns. The control module tests for this by commanding the EVAP purge solenoid OFF, closed; and vent solenoid ON, closed; sealing the system, and monitoring the Fuel Tank Pressure (FTP) for an increase in vacuum. If the control module detects that EVAP system vacuum increases above a calibrated value, DTC P0496 will set.