Engine Controls - 4.3L - Troubleshooting & Diagnosis: Diagnosis Chevrolet Silverado 1500

Important Preliminary Inspections Before Beginning

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 control module 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-238295-S35183712762006072400000) .
4. Verify the customer concern and locate the correct symptom. Inspect the items indicated under that symptom.
5. 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.
6. Inspect for improper installation of electrical components if an intermittent condition exists. Inspect for aftermarket theft deterrent devices, lights, and cellular phones. If you can not locate an intermittent condition, a cellular phone communication signal may cause the condition.
7. If the intermittent condition exists as a start and then stall, test for DTCs relating to the vehicle theft deterrent system.

Use the following tables when diagnosing a symptom complaint

1. «Hard Start»(ref-238229-S28716473962006072400000)
2. «Surges/Chuggles»(ref-238229-S28702158232006072400000)
3. «Lack of Power, Sluggishness, or Sponginess»(ref-238229-S33409065422006072400000)
4. «Detonation/Spark Knock»(ref-238229-S31268082562006072400000)
5. «Hesitation, Sag, Stumble»(ref-238229-S24551883402006072400000)
6. «Cuts Out, Misses»(ref-238229-S07652793642006072400000)
7. «Poor Fuel Economy»(ref-238229-S20241064732006072400000)
8. «Poor Fuel Fill Quality»(ref-238229-S05535446062006072400000)
9. «Rough, Unstable, or Incorrect Idle and Stalling»(ref-238229-S08489885372006072400000)
10. «Dieseling, Run-On»(ref-238229-S19826926732006072400000)
11. «Backfire»(ref-238229-S39389266792006072400000)

Circuit Description

Ignition voltage is supplied to the malfunction indicator lamp (MIL). The powertrain control module (PCM) 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 powertrain control module (PCM) 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 ignition relay is a normally open relay. The relay armature is held in the open position by spring tension. When the ignition switch is turned to the run or start position, current will flow through the relay coil. A wire connected to the other end of the relay coil completes the path to ground. The electomagnetic field created by the relay coil, overcomes the spring tension and moves the armature allowing the relay contacts to close. The closed relay contacts allow current to flow from the battery to the following fuses

1. The PCM 1 fuse
2. The ETC/ECM fuse
3. The INJ 1 fuse
4. The INJ 2 fuse
5. The SBA fuse, if equipped

When the ignition switch is turned to the OFF position, the electromagnetic field collapses. This action allows the spring tension to move the armature away from the relay contacts, which interrupts current flow to the fuses.

If the ignition relay fails to close, the engine will crank, but will not run. The class 2 communications will be available with the use of a scan tool.

The ignition relay table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test (Non-HP2) or Battery Inspection/Test (HP2) in Engine Electrical.

Ignition 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 2 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 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

Fuel Pump Electrical Circuit Diagnosis

The control module enables the appropriate fuel injector pulse 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 to 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 customer's 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 (3.38 oz) specified cylinder with 1 ml (0.034 oz) graduation marks, fill the cylinder with fuel to the 90 ml (3.04 oz) mark.
2. Add 10 ml (0.34 oz) of water in order to bring the total fluid volume to 100 ml (3.38 oz) 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 (0.34 oz). For example, if the volume of the lower layer is increased to 15 ml (0.51 oz), 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 (0.53 qt) of fuel.
2. Place the container 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.
3. Observe the fuel sample. If any physical contaminants or water are present, clean the fuel system. Refer to «Fuel System Cleaning»(ref-238194-S38858636392006072400000) .

Test Procedure

1. Test the fuel composition using J 44175 Fuel Composition Tester and J44175-3 Instruction Manual. See «Special Tools»(ref-238194-S31387655202006072400000) .
2. If water appears in the fuel sample, clean the fuel system. Refer to «Fuel System Cleaning»(ref-238194-S38858636392006072400000) .
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-238194-S38858636392006072400000) .

Fuel Composition Test Examples

The engine idle speed is controlled by the idle air control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is supplied current by 2 circuits from the powertrain control module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed diagnostic trouble code (DTC) sets.

Inspect for the following conditions

1. High resistance in an IAC valve control circuit
2. The correct positive crankcase ventilation (PCV) valve, properly installed, and proper operation of the PCV valve
3. Proper operation and installation of all air intake components
4. Proper installation and operation of the mass air flow (MAF) sensor, if equipped
5. A tampered with or damaged throttle stop screw
6. A tampered with or damaged throttle plate, throttle shaft, throttle linkage, or cruise control linkage, if equipped
7. A skewed high throttle position (TP) sensor
8. Excessive deposits in the IAC passage or on the IAC pintle
9. Excessive deposits in the throttle bore or on the throttle plate
10. Vacuum leaks
11. A high or unstable idle condition could be caused by a non-IAC system condition that can not be overcome by the IAC valve. Refer to «Symptoms - Engine Controls»(ref-238229-S20319341182006072400000) .
12. If the condition is determined to be intermittent, refer to «Testing for Intermittent Conditions and Poor Connections»(ref-238178-S33329058682006072400000) .

Engine mechanical conditions may prevent the distributor from rotating. Inspect the following conditions if the distributor rotor does not rotate

1. A broken distributor drive shaft
2. A worn or broken distributor drive gear
3. A worn or broken camshaft timing chain and gears

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Refer to Testing for Intermittent Conditions and Poor Connections . If a repair is necessary, refer to Wiring Repairs .

Diagnostic Fault Information

Inspection/Maintenance (I/M) System Set Procedure

1. Ensure that the vehicle meets the conditions for a cold start listed above. If the evaporative emission (EVAP) I/M System Status indicator displays NO, perform the EVAP Service bay test if available. If the EVAP Service bay test is NOT available, it may take up to 6 drive cycles, with up to 17 hours between drive cycles, for the EVAP I/M System Status indicator to transition to YES. If the O2S Heater System Status indicator displays NO, ensure that the ignition has been turned OFF for at least 10 hours.
2. Set the vehicle parking brake and ensure the vehicle is in park for automatic transmission or neutral for manual transmission.
3. Turn OFF all accessories; HVAC system, other electrical loads, including aftermarket/add-on equipment, etc.
4. Start and idle the engine for at least 2 minutes and until 65°C (149°F) is achieved.
5. Run the engine for 6.5 minutes within the following conditions: MAF parameter between 4-30 g/s Engine speed steady between 1000-3000 RPM
6. Return the engine to idle for 1 minute.
7. Apply and hold brake pedal, and shift to Drive for automatic, or apply clutch pedal for manual and operate the vehicle within the following conditions for 2 minutes: Depress the accelerator pedal until throttle position (TP) sensor angle is more than 2 percent. Mass air flow (MAF) signal between 15-30 g/s RPM steady between 1200-2000 RPM
8. Tip: Do NOT touch the accelerator pedal during the idle period. A change in TP Sensor angle or an increase in engine speed may invalidate this portion of the test. Release the accelerator pedal and shift the vehicle to Park for automatic, or Neutral and release clutch pedal for manual, and allow the engine to idle for 2 minutes.
9. Quickly depress the accelerator pedal until TP Sensor Angle is more than 8 percent and return to idle, repeat 3 times.
10. Allow engine to idle for at least 2 minutes.
11. Release the parking brake and drive vehicle at 24 km/h (15 mph) or slower for 2 minutes.
12. Continue to drive the vehicle for at least 5.5 miles between 45-112 km/h (28-70 mph) with the vehicle reaching at least 80 km/h (50 mph).
13. Release the accelerator pedal for at least 2 seconds. This will allow the vehicle to enter decel fuel cut-off.
14. Depress the accelerator pedal until the TP Sensor angle is increased 3-20 percent and maintain a safe speed for 1 minute.
15. Safely stop the vehicle, with the engine in drive for automatic or in neutral with the clutch pedal depressed and parking brake applied for manual, idle for 2 minutes.
16. Shift to Park for automatic and apply the parking brake, or neutral and release clutch pedal for manual.
17. Turn OFF the ignition and exit the vehicle. Do NOT disturb the vehicle for 60 minutes.
18. Observe the Inspection/Maintenance (I/M) System Status with a scan tool. All of the I/M System Status indicators should display YES. If the EVAP I/M System Status indicator displays NO, turn OFF the ignition for 17 hours, ensure that the vehicle meets the conditions for a cold start, and repeat steps 12-18 six more times, or until the EVAP I/M System Status indicator transitions to YES. If the indicator continues to display NO, refer to the «Inspection/Maintenance (I/M) System DTC Table»(ref-238229-S12873167012006072400000) to identify the DTCs that did not run. Follow the Conditions for Running the DTC in order to set the EVAP I/M System Status indicator

1. If any of the I/M System Status indicators display NO, refer to the «Inspection/Maintenance (I/M) System DTC Table»(ref-238229-S12873167012006072400000) for the indicator which did not display YES. The I/M System DTC Table identifies the DTCs associated with each I/M System Status Indicator. Follow the Conditions for Running the DTC in order to set the associated status indicator.

Inspection/Maintenance (I/M) System DTC Table

Inspection/Maintenance (I/M) System DTC Table