Engine Control System - 5.3L - Troubleshooting: Diagnosis GMC Envoy II

Important Preliminary Inspections Before Starting

Perform Diagnostic System Check - Vehicle in Vehicle DTC Information before using the symptom tables, and verify that all of the following are true

1. The engine control module (ECM) and malfunction indicator lamp (MIL) are operating correctly.
2. There are no DTCs stored.
3. The scan tool data is within the normal operating range, refer to «Scan Tool Data List»(ref-200443-S18855418062005102000000) .
4. Verify the customer concern and locate the correct symptom in the table of contents. Inspect the items indicated under that symptom.

Visual/Physical Inspection

Several of the symptom procedures ask for a careful visual and physical inspection. This step is extremely important. The visual and physical inspection can lead to correcting a problem without further inspections, and can save valuable time. Ensure that

1. The ECM grounds are clean, tight, and in the proper location.
2. The vacuum hoses are not split or kinked, and properly connected, as shown on the Vehicle Emission Control Information label. Inspect thoroughly for any type of leak or restriction.
3. The mass air flow (MAF) sensor is properly installed. The arrows on the plastic portion of the sensor must point toward the engine.
4. The air intake ducts are not collapsed or damaged.
5. There are no leaks at the throttle body mounting area, the MAF sensor, or the intake manifold sealing surfaces.
6. The ignition wires are not cracked, brittle, or carbon tracked.
7. The engine harness wiring and terminals are properly connected and are not pinched or cut.

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 Testing for Intermittent Conditions and Poor Connections .

The powertrain relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the powertrain relay coil and the armature contact at all times. The engine control module (ECM) supplies the ground path to the relay coil control circuit via an internal integrated circuit called an output driver module (ODM). When the ECM commands the relay ON, the relay coil creates an electromagnetic field. This electromagnetic field overcomes the spring tension and pulls the armature contact into the stationary contact of the relay load circuit. The closing of the relay contacts allows current to flow from the battery to the following fuses

1. The INJ A Fuse
2. The INJ B Fuse
3. The TAC fuse
4. The ENG 1 Fuse
5. The 02 A Fuse
6. The 02 B Fuse

When the ignition switch is turned to the OFF position, power is interrupted to the ODM in the ECM and the powertrain relay electromagnetic field collapses. This action allows the spring tension pulling on the armature to separate from the relay load circuit contact, which interrupts current flow to the fuses. If the powertrain relay fails to close, the engine will crank but will not run. The GMLAN and class II data communications will be available with the use of a CAN module and scan tool. The powertrain relay will remain powered up for 5 seconds after the ignition switch is turned OFF. The powertrain relay system diagnosis table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test (Non-HP2) in Engine Electrical.

Powertrain Relay Diagnosis

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.

Test Procedure

1. Test the fuel composition using J 44175 Fuel Composition Tester and J 44175-3 Instruction Manual.
2. If water appears in the fuel sample, perform the following steps: Clean the fuel system. Refer to «Fuel System Cleaning»(ref-200373-S28692640482005102000000) . 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-200373-S28692640482005102000000) .

Fuel Composition Test Examples

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 .

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 .

To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the Displacement On Demand (DOD) system ON to deactivate engine cylinders 1 and 7 on the left bank, and cylinders 4 and 6 on the right bank, switching to a V4 mode. The DOD systems use an electro-hydraulic actuator device called the valve lifter oil manifold (VLOM) assembly. The VLOM consists of 4 electrically operated normally closed solenoids that directs engine oil pressure to the deactivating DOD valve lifters. All 4 VLOM solenoids are connected in parallel to a fused ignition 1 voltage circuit supplied by the powertrain relay. The ground or control circuit for each solenoid is connected to an individual low side driver internal to the ECM. When all enabling conditions for V4 mode are met, the ECM will command the low side driver to turn ON, grounding each VLOM solenoid control circuit, in engine firing order sequence.

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, secondary air injection (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 (BARO) 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

1. At least 17 hours have elapsed since the last drive cycle met the Conditions for Running.
2. The difference between the start-up engine coolant temperature (ECT) and the start-up intake air temperature (IAT) is less than 8°C (14.4°F).
3. The barometric pressure (BARO) is more than 74 kPa.
4. The start-up ECT is between 4-30°C (39-86°F).
5. The start-up IAT is between 4-30°C (39-86°F).
6. The fuel level is between 15-85 percent.
7. The battery voltage is between 10-18 volts.
8. The fuel level does not increase more than 9 percent during this drive cycle.
9. The engine run time is at least 10 minutes.
10. The vehicle has been driven at least 5 km (3.15 miles) this drive cycle.
11. The estimated ambient temperature at the end of this drive cycle is between 2-32°C (36-89°F).
12. The shutdown ECT is at least 70°C (158°F).
13. The ignition is turned OFF for at least 1 hour after this drive cycle.

Extreme high or low ambient temperatures may prevent the EVAP System Tests from initiating. A loose fuel cap may cause a test to abort or fail and prevent the I/M System Status from updating. A failed or aborted diagnostic will require the vehicle to cool down in order to meet the enable criteria for another drive cycle.

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 diagnostic does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information. This will give an indication of why the test does not complete. Some diagnostics 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 an A/C compressor clutch turning ON, may cause the diagnostic to abort.

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 engine control temperature (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