Engine Control System & Component Tests - 4.3L: Diagnosis GMC Savana H2500

ALCOHOL/CONTAMINANTS IN FUEL DIAGNOSIS WITH SPECIAL TOOL

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS .

Diagnostic Procedures

1. Turn on the Fuel Composition Tester (J-44175).
2. Verify the fuel composition tester is operational by measuring the AC frequency output with a DVOM. A frequency without a fuel sample in the test cell indicates that the tester is working correctly.
3. Install fuel pressure gauge.
4. Close bleed valve on fuel pressure gauge.
5. Place the bleed hose of the fuel pressure gauge into the 100 ml beaker.
6. Using scan tool, command fuel pump relay on.
7. Slowly open the bleed valve on the fuel pressure gauge, until an adequate fuel sample is obtained.
8. If water appears in the fuel sample, clean the fuel system and replace the fuel in the vehicle.
9. Pour fuel sample from the beaker into the tester until the level of the fuel is at the top of each fuel test port.
10. Observe the diagnostic LEDs on the fuel composition tester. If the Red fuel diagnostic LED is illuminated, a fuel contamination condition exists. Refer to «FUEL SYSTEM CLEANING»(ref-153186-S26515672532003032400000) .
11. Measure the output frequency of the fuel composition tester.
12. Subtract 50 from the reading on the DVOM to obtain the percentage of alcohol in the fuel sample.
13. If fuel sample contains more than 10 percent ethanol, add gasoline to the fuel tank or replace the fuel in the vehicle.

ALCOHOL/CONTAMINANTS IN FUEL DIAGNOSIS WITHOUT SPECIAL TOOL

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS .

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 procedures to test the fuel quality.

1. Using a 3.38 oz. (100 ml) graduated cylinder with 0.034 oz. (1 ml) graduation marks, fill the cylinder with fuel to the 3.04 oz. (90 ml) mark.
2. Add 0.34 oz. (10 ml) of water in order to bring the total fluid volume to 3.38 oz. (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 0.34 oz. (10 ml). For example, if the volume of the lower layer is increased to 0.51 oz. (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 0.53 qt. (0.5 liter) of fuel.
2. Place 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 fuel sample. If any physical contaminants or water are present, clean fuel system. Refer to «FUEL SYSTEM CLEANING»(ref-153186-S26515672532003032400000) .

FUEL INJECTOR BALANCE TEST WITHOUT SPECIAL TOOL

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS .

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158087-S34600730772003091100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Perform «FUEL INJECTOR COIL TEST»(ref-153186-S20453890052003032400000). After performing Fuel Injector Coil Test, go to next step.
3. Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
4. Turn ignition off. Turn OFF all accessories. Install fuel pressure gauge. Turn ignition on, with engine off. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 48-54 psi (334-375 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS»(ref-152740-S01575235222003022400000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
5. Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM DIAGNOSIS»(ref-152740-S01575235222003022400000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article. If no, go to next step.
6. Disconnect multi-way harness connector of fuel injectors. Connect Fuel Injector Tester (J-39021) to ignition 1 voltage circuit terminal and appropriate fuel injector control circuit terminal using Connector Test Adapter Kit (J-35616-A). Set amperage supply selector switch on fuel injector tester to Balance Test.5-2.5-amp position. Command fuel pump ON and then OFF with scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. see scheme 11 Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS»(ref-152942-S02035049812003030500000) in TROUBLE SHOOTING - NO CODES - 4.3L CHEVY EXPRESS & SAVANA article.
7. Replace affected fuel injectors. After repairs, go to next step.
8. Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS»(ref-152942-S02035049812003030500000) in TROUBLE SHOOTING - NO CODES - 4.3L CHEVY EXPRESS & SAVANA article.

FUEL INJECTOR BALANCE TEST WITH TECH 2

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS .

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158087-S34600730772003091100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Perform «FUEL INJECTOR COIL TEST»(ref-153186-S20453890052003032400000) . After performing Fuel Injector Coil Test, go to next step.
3. Observe ECT parameter with scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
4. Turn ignition off. Turn OFF all accessories. Install fuel pressure gauge. Turn ignition on, with engine off. Command fuel pump ON with scan tool. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 48-54 psi (334-375 kPa)? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS»(ref-152740-S01575235222003022400000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
5. Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to «FUEL SYSTEM DIAGNOSIS»(ref-152740-S01575235222003022400000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article. If no, go to next step.
6. With scan tool, select Fuel Injector Balance Test function, within Special Functions menu. Select an injector to be tested. Press ENTER. This will prime fuel system. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing PULSE INJECTOR button on scan tool. This will energize injector and decrease fuel pressure. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Press ENTER again to bring you back to Select Injector screen. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value that is more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to «SYMPTOMS»(ref-152942-S02035049812003030500000) in TROUBLE SHOOTING - NO CODES - 4.3L CHEVY EXPRESS & SAVANA article.
7. Replace affected fuel injectors. After repairs, go to next step.
8. Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS»(ref-152942-S02035049812003030500000) in TROUBLE SHOOTING - NO CODES - 4.3L CHEVY EXPRESS & SAVANA article.

FUEL INJECTOR CIRCUIT DIAGNOSIS

A malfunction in the fuel injection circuit can set a DTC. For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.

FUEL INJECTOR COIL TEST

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS .

Circuit Description

Control module enables appropriate fuel injector on intake stroke for each cylinder. A voltage is supplied directly to fuel injectors. Control module controls each fuel injector by grounding 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. Fuel injector coil windings are affected by temperature. Resistance of fuel injector coil windings will increase as temperature of fuel injector increases.

Diagnostic Aids

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

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158087-S34600730772003091100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
3. Disconnect the multi-way harness connector of the fuel injectors. Using a DVOM, measure resistance of each fuel injector between the ignition 1 circuit and the fuel injector control circuit, at the multi-way connector. Is resistance within the 11-14 ohms for each injector? If yes, go to «FUEL INJECTOR BALANCE TEST WITHOUT SPECIAL TOOL»(ref-153186-S41808286432003032400000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(ref-153186-S26802195532003032400000) . If no, go to step 6 .
4. Disconnect the multi-way harness connector of the fuel injectors. Using DVOM, measure the resistance of each fuel injector between the ignition 1 voltage circuit and the fuel injector control circuit, at the multi-way connector. Record each fuel injector resistance value. Subtract the lowest resistance value from the highest resistance value. Is difference equal to or less than 3 ohms? If yes, go to «FUEL INJECTOR BALANCE TEST WITHOUT SPECIAL TOOL»(ref-153186-S41808286432003032400000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(ref-153186-S26802195532003032400000) . If no, go to next step.
5. Add all fuel injector resistance values to obtain a total resistance value. Divide total resistance value by number of fuel injectors to obtain an average resistance value. Subtract lowest and highest individual fuel injector resistance values from average resistance value. Replace fuel injector that displays greatest resistance difference, more or less than average. After repairs, go to step 7 .
6. Replace fuel injector(s) that are outside of 11-14 ohms range. After repairs, go to next step.
7. Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

Scheme 10

Scheme 11

The control module enables fuel pump relay when ignition switch is turned on. The control module will disable fuel pump relay within 2 seconds unless control module detects ignition reference pulses. The control module continues to enable fuel pump relay as long as ignition reference pulses are detected. The control module disables fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and ignition remains on.

1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158087-S34600730772003091100000) under SELF DIAGNOSTIC SYSTEM in SELF DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. After performing diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Using scan tool, command fuel pump relay on and off. Repeat commands as necessary. Does fuel pump turn on and off? If yes, problem is intermittent. If no, go to next step.
3. Using scan tool, command fuel pump relay on and off. Fuel pump relay is located in underhood fuse/relay block. (Scheme 10) Do you hear a click when you command fuel pump relay on and off? If yes, go to step 9. If no, go to next step.
4. Turn ignition off. Remove fuel pump relay. Turn ignition on, with engine off. Probe control circuit of fuel pump relay with a test light that is connected to a good ground. (Scheme 11) Command fuel pump relay ON and OFF with a scan tool. Does test light turn ON and OFF? If yes, go to next step. If no, go to step 6.
5. Connect a test light between control circuit of fuel pump relay and ground circuit of fuel pump relay. Command fuel pump relay on and off with a scan tool. Does test light turn on and off? If yes, go to step 19. If no, go to step 22.
6. Does test light remain illuminated with each command? If yes, go to next step. If no, go to step 8.
7. Test control circuit of fuel pump relay for a short to voltage. (Scheme 11) Did you find and correct condition? If yes, go to step 27. If no, go to step 26.
8. Test control circuit of fuel pump relay for a short to ground or an open. Did you find and correct condition? If yes, go to step 27. If no, go to step 20.
9. Turn ignition on, with engine off. Does fuel pump operate continuously? If yes, go to next step. If no, go to step 11.
10. Turn ignition off. Remove fuel pump relay. Turn ignition on, with engine off. Does fuel pump operate continuously? If yes, go to step 21. If no, go to step 25.
11. Inspect fuel pump fuse. Is fuse open? If yes, go to next step. If no, go to step 14.
12. Test supply voltage circuit of fuel pump for a short to ground between fuel pump fuse and fuel pump. Replace fuel pump fuse, if necessary. Did you find and correct condition? If yes, go to step 27. If no, go to next step.
13. Connect all disconnected electrical components. Install a new fuel pump fuse. Command fuel pump relay on with a scan tool. Inspect fuel pump fuse. Is fuse open? If yes, go to step 24. If no, problem is intermittent.
14. Turn ignition off. Remove fuel pump relay. Turn ignition on, with engine off. Probe ignition 1 voltage circuit of fuel pump relay, switch side, with a test light connected to a good ground. Does test light illuminate? If yes, go to next step. If no, go to step 23.
15. Connect a 20-amp fused jumper wire between ignition 1 voltage circuit of fuel pump relay and supply voltage circuit of fuel pump. Does fuel pump operate? If yes, go to step 19. If no, go to next step.
16. Test supply voltage circuit of fuel pump for an open or high resistance between fuel pump relay and fuel pump. Did you find and correct condition? If yes, go to step 27. If no, go to next step.
17. Test ground circuit of fuel pump for an open or high resistance. Did you find and correct condition? If yes, go to step 27. If no, go to next step.
18. Test for an intermittent and for a poor connection at fuel sender cover. Did you find and correct condition? If yes, go to step 27. If no, go to step 24.
19. Test for an intermittent and for a poor connection at fuel pump relay. Did you find and correct condition? If yes, go to step 27. If no, go to step 25.
20. Test for an intermittent and for a poor connection at PCM. Did you find and correct condition? If yes, go to step 27. If no, go to step 26.
21. Repair short to voltage in supply voltage circuit of fuel pump. After repairs, go to step 27.
22. Repair open or high resistance in ground circuit of fuel pump relay. After repairs, go to step 27.
23. Repair open in ignition 1 voltage circuit of fuel pump relay. After repairs, go to step 27.
24. Inspect for poor connections at fuel pump, within fuel tank, before replacing fuel pump. Replace fuel sender. Replace fuel pump fuse, if necessary. After repairs, go to step 27.
25. Replace fuel pump. After replacing fuel pump, go to step 27.
26. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM programing. After replacing PCM, go to next step.
27. Operate system in order to verify repair. Did you correct condition? If yes, system is okay. If no, go to step 2.

FUEL SYSTEM PRESSURE TEST

Note. For fuel system pressure testing, see FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.

1. Operate vehicle under condition of customer's concern. Under high temperature conditions fuel vapors may increase to point of EVAP canister vapor saturation. Fuel vapors would then be released into atmosphere. Once engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
2. Movement of EVAP pipes or fuel pipes may help find an intermittent condition.

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158087-S34600730772003091100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
2. Raise vehicle. Inspect fuel tank and fuel pipes for damage or external leaks. Did you find fuel leaking from fuel tank? If yes, go to step 6 . If no, go to next step.
3. Turn ignition on, with engine off. Using scan tool, command fuel pump ON. Inspect for fuel leaking from fuel pipes. Did fuel leak from fuel pipes? If yes, go to step 7 . If no, go to next step.
4. Turn ignition off. Install Fuel Tank Cap Adapter (J-41415-40). Connect Evaporative Emissions System Tester (J-41413-200) to fuel tank cap adapter. Turn ignition on, with engine off. Using scan tool, seal EVAP system. DO NOT exceed 15 in. H2O. With EVAP pressure/purge diagnostic station, pressurize fuel tank. Did fuel leak from fuel tank? If yes, go to step 6 . If no, go to next step.
5. With EVAP pressure/purge diagnostic station, maintain pressure in fuel tank. With Ultrasonic Leak Detector (J-41416), test for leaks above fuel level in following locations: Fuel tank, fill limiter vent valve, pressure relief valve and rollover valves. Fuel sender housing and fuel sender seal. Fuel Tank Pressure (FTP) sensor seal. EVAP vapor pipes. Fuel fill pipe and hose. Did you locate a fuel leak? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-153186-S13922405232003032400000) .
6. Replace fuel tank. After repairs, system is okay.
7. Replace leaking fuel pipe. After repairs, system is okay.
8. Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

IDLE AIR CONTROL SYSTEM DIAGNOSIS

Note. For circuit reference, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS .

Inspect for the following conditions

1. High resistance in an IAC valve control circuit.
2. The correct 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 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 TP sensor.
8. Excessive deposits in the IAC passage or on 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 problem that cannot be overcome by the IAC valve.
12. For intermittent conditions, see «INTERMITTENTS»(ref-152942-S41769628812003030500000) in TROUBLE SHOOTING - NO CODES - 4.3L CHEVY EXPRESS & SAVANA article.

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158087-S34600730772003091100000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Set parking brake and block drive wheels. Start engine. Turn OFF all accessories. Using scan tool in RPM Control function, slowly increment engine speed to 1700 RPM, then to 600 RPM, then to 1700 RPM. Exit the RPM Control function. Did the engine speed parameter stabilize within 100 RPM less than the commanded engine speed or within 200 RPM above the commanded RPM? If yes, go to «DIAGNOSTIC AIDS»(ref-153186-S21294130312003032400000). If no, go to next step.
3. Turn ignition off. Disconnect the IAC valve. Connect an IAC Motor Driver (J-37027-1A) to the IAC valve. Start engine. Using IAC motor driver, command the IAC valve in until 600 RPM is reached. Command the IAC valve out until 1700 RPM is reached. Return engine speed to the desired idle speed parameter. Did engine speed parameter steadily decrease to 600 RPM and steadily increase to 1700 RPM when IAC valve was commanded in and out? If yes, go to step 5. If no, go to next step.
4. Did you observe an excessively high idle condition that could not be controlled with the IAC motor driver? If yes, go to step 11. If no, go to step 12.
5. Connect a test light between one of the IAC valve control circuits and a good ground. Start engine. Observe the IAC Counts parameter with scan tool. Using IAC Motor Driver (J-37027-1), command high RPM until the IAC Counts parameter starts to increment. Command low RPM until the IAC Counts parameter starts to increment. Return engine speed to the desired idle speed parameter. Repeat procedure for the other 3 IAC valve control circuits. Did the test light remain on, never flashing, while the IAC counts were incrementing for any of the IAC valve control circuits? If yes, go to step 10. If no, go to next step.
6. Did the test light remain off, never flashing, while the IAC counts were incrementing for any of the IAC valve control circuits? If yes, go to step 9. If no, go to next step.
7. Connect a test light between the IAC coil "A" low control circuit and IAC coil "A" high control circuit. (Scheme 12) Observe the IAC Counts parameter with a scan tool and test light. Using IAC motor driver, command high RPM until the IAC counts parameter starts to increment. Command low RPM until the IAC counts parameter starts to increment. Return the engine speed parameter to the desired idle speed parameter. Repeat procedure with test light connected between the IAC coil "B" low control circuit and IAC coil "B" high control circuit. Did the test light stay illuminated, never flashing, while the IAC counts were incrementing? If yes, go to next step. If no, go to step 17.
8. Test for an intermittent and for a poor connection at the IAC valve. Did you find and correct the condition? If yes, go to step 18. If no, go to step 13.
9. Turn ignition off. Disconnect PCM. Test the circuit where the test light remained OFF for an open circuit, short to ground, or short to another IAC valve control circuit. Did you find and correct the condition? If yes, go to step 18. If no, go to step 13.
10. Turn ignition on. Test the IAC valve control circuit where the test light remained illuminated for a short to voltage, or short to another IAC valve control circuit. Did you find and correct the condition? If yes, go to step 18. If no, go to step 13.
11. Inspect throttle body for damage and tampering, a skewed TP sensor signal, throttle lever screw for tampering (if equipped) or vacuum leaks. Inspect for faulty or incorrectly installed PCV valve and hose, if equipped. Inspect throttle shaft for binding, throttle linkage or cruise control linkage for binding, if equipped. Remove IAC valve. Inspect for debris in IAC passage, excessive deposits on throttle plate, excessive deposits in throttle bore, or excessive deposits on IAC valve pintle. Did you find and correct the condition? If yes, go to step 18. If no, go to step 15.
12. Inspect throttle body for damage and tampering, throttle lever screw for tampering (if equipped), excessive deposits on throttle plate, or restricted air intake system. Inspect for collapsed or clogged air intake duct, before and after the air filter element, a restricted air filter element, restriction at throttle body intake screen, if equipped. Remove IAC valve. Inspect for excessive deposits on the IAC valve pintle and in IAC valve passage. Did you find and correct the condition? If yes, go to step 18. If no, go to step 15.
13. Test for an intermittent and for a poor connection at PCM. Did you find and correct the condition? If yes, go to step 18. If no, go to next step.
14. Disconnect PCM. Test all IAC valve control circuits for high resistance. Did you find and correct the condition? If yes, go to step 18. If no, go to step 17.
15. Test for an intermittent and for a poor connection at the IAC valve. Did you find and correct the condition? If yes, go to step 18. If no, go to next step.
16. Replace IAC valve. After replacing IAC valve, go to step 18.
17. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Program replacement PCM. After repairs, go to next step.
18. Reconnect any disconnected components. Clear DTCs with scan tool. Turn ignition off for 30 seconds. Attempt to reproduce the original symptoms to verify the repair. Did you verify the repair? If yes, go to next step. If no, go to step 2.
19. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-158087-S41901059152003091100000) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. If no, system is okay.

Scheme 12

ELECTRONIC IGNITION SYSTEM DIAGNOSIS

See DISTRIBUTOR IGNITION SYSTEM under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.

EVAP Control System Diagnosis

For EVAP control system diagnosis, see appropriate INSPECTION/MAINTENANCE PROCEDURES in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.