Engine Controls - System & Component Testing - 4.3: Diagnosis Chevrolet Silverado 1500 HD

Circuit Description

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 electromagnetic 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: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA, if equipped.

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

Diagnostic Procedures

1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158208-S20709970632003091700000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article. After performing diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Remove underhood fuse/relay block cover. Probe the following fuses with a test light connected to a good ground: PCM 1, ETC/ECM, INJ 1, INJ 2, and SBA fuses, if equipped. (Scheme 20) Does test light illuminate on at least one test point of each fuse? If yes, go to next step. If no, go to step 10.
3. Turn ignition off. Probe both test points of the PCM 1 fuse with a test light connected to a good ground. Does the test light illuminate on either test point of the fuse? If yes, go to next step. If no, go to step 30.
4. Turn ignition off. Remove ignition relay from the underhood fuse/relay block. Probe ignition 1 voltage circuit of the ignition relay at the underhood fuse/relay block with a test light connected to a good ground. Does test light illuminate? If yes, go to step 7. If no, go to next step.
5. Test the relay load bus bar of the underhood fuse/relay block between ignition relay and fuses to the circuit components for a short to battery positive voltage. Did you find a condition? If yes, go to step 29. If no, go to next step.
6. Turn ignition off. Remove the following fuses from the underhood fuse/relay block: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA, if equipped. Probe the fuse terminals in the underhood fuse/relay block with a test light that is connected to a good ground. Does the test light illuminate at any of the fuse terminals? If yes, diagnose engine electrical system. If no, go to step 27.
7. Turn ignition off. Disconnect negative battery cable. Disconnect underhood fuse/relay block electrical connector that contains the ignition 1 voltage circuit for the ignition relay. Disconnect ignition switch electrical connector that contains the ignition 1 voltage circuit for ignition relay. Reconnect negative battery cable. Test the ignition 1 voltage circuit for a short to battery positive voltage. Did you find and correct the condition? If yes, go to step 30. If no, go to next step.
8. Turn ignition off. Probe ignition 1 voltage terminal on ignition switch side of the ignition switch electrical connector with a test light connected to a good ground. Does the test light illuminate? If yes, go to step 28. If no, go to next step.
9. Test the ignition 1 voltage bus bar circuit in the underhood fuse/relay block for a short to battery positive voltage. Did you find a condition? If yes, go to step 29. If no, go to step 27.
10. Turn ignition off. Inspect the 40-amp IGN "B" fuse in the underhood fuse/relay block. Is fuse open? If yes, go to next step. If no, go to step 18.
11. Remove the 40-amp IGN "B" fuse from the underhood fuse/relay block. Probe both fuse terminals in the underhood fuse/relay block with a test light that is connected to a good ground. Does the test light illuminate on at least one fuse terminal? If yes, go to next step. If no, go to step 17.
12. Test the ignition 1 voltage circuit between the ignition switch and the underhood fuse/relay block for a short to ground. Did you find and correct the condition? If yes, go to step 30. If no, go to next step.
13. Test the ignition switch assembly for a short to ground. Did you find a condition? If yes, go to step 28. If no, go to next step.
14. Test the battery positive voltage circuit between the underhood fuse/relay block and ignition switch for a short to ground. Did you find and correct the condition? If yes, go to step 30. If no, go to next step.
15. Test the battery positive voltage bus bar circuit of the underhood fuse/relay block between the 40-amp IGN "B" fuse and ignition switch for a short to ground. Did you find a condition? If yes, go to step 29. If no, go to next step.
16. Test the ignition 1 voltage bus bar circuit of the underhood fuse/relay block that contains the ignition relay for a short to ground. Did you find a condition? If yes, go to step 29. If no, go to step 27.
17. Turn ignition off. Probe the mounting stud for the battery positive cable at the underhood fuse/relay block with a test light connected to a good ground. Does the test light illuminate? If yes, go to step 29. If no, diagnose engine electrical system.
18. Turn ignition off. Remove ignition relay from underhood fuse/relay block. Probe the battery positive voltage circuit of the ignition relay at the underhood fuse/relay block with a test light connected to a good ground. Does test light illuminate? If yes, go to next step. If no, go to step 29.
19. Turn ignition on, with engine off. Probe the ignition 1 voltage circuit of the ignition relay at the underhood fuse/relay block with a test light connected to a good ground. Does the test light illuminate? If yes, go to step 23. If no, go to next step.
20. Turn ignition off. Test the ignition 1 voltage circuit between the ignition switch and the underhood fuse/relay block for a high resistance or for an open. Did you find and correct the condition? If yes, go to step 30. If no, go to next step.
21. Test the ignition switch assembly for a high resistance or for an open. Did you find a condition? If yes, go to step 28. If no, go to next step.
22. Test the battery positive voltage circuit between the ignition switch and the underhood fuse/relay block for a high resistance or for an open. Did you find and correct the condition? If yes, go to step 30. If no, go to step 29.
23. Turn ignition on, with engine off. Probe the coil ground circuit of the ignition relay at the underhood fuse/relay block with a test light connected to battery voltage. Does test light illuminate? If yes, go to step 25. If no, go to next step.
24. Turn ignition off. Disconnect negative battery cable at battery. Disconnect the underhood fuse/relay block electrical connectors. Test the coil ground circuit of the ignition relay at the underhood fuse/relay block electrical connector for a high resistance or for an open. Did you find and correct the condition? If yes, go to step 30. If no, go to step 29.
25. Turn ignition off. Jumper the ignition relay battery positive voltage circuit and ignition relay load circuit together at the underhood fuse/relay block with a 20-amp fused jumper wire. Probe the following fuses with a test light that is connected to a good ground: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA, if equipped. Does the test light illuminate on at least one test point of each fuse? If yes, go to next step. If no, go to step 29.
26. Test for an intermittent and for a poor connection at the underhood fuse/relay block, ignition relay connector location. Did you find a condition? If yes, go to step 29. If no, go to next step.
27. Replace ignition relay. After replacing relay, go to step 30.
28. Replace ignition switch. After replacing ignition switch, go to step 30.
29. Replace underhood fuse/relay block. After replacing fuse/relay block, go to next step.
30. Replace any open fuses. Turn ignition off for 30 seconds. Attempt to start the engine. Does the engine start and run? If yes, go to next step. If no, go to «NO-START - ENGINE CRANKS OKAY»(ref-152743-S24308457622003022400000) under NO-START in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO article.
31. Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Let engine reach operating temperature. Are re any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-158208-S06912544392003091700000) in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article. If no DTC(s) are set, system is okay.

ALCOHOL/CONTAMINANTS IN FUEL DIAGNOSIS WITH SPECIAL TOOL

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

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-153194-S21557135382003032400000) .
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 .

Note. 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-153194-S21557135382003032400000) .

FUEL INJECTOR BALANCE TEST WITHOUT SPECIAL TOOL

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

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158208-S20709970632003091700000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Perform «FUEL INJECTOR COIL TEST»(ref-153194-S21564381642003032400000). 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 PRESSURE TEST»(ref-152743-S07134794452003022400000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO 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 PRESSURE TEST»(ref-152743-S07134794452003022400000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO 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 17 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-152982-S33481225962003030700000) in TROUBLE SHOOTING - NO CODES - 4.3L SIERRA & SILVERADO 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-152982-S33481225962003030700000) in TROUBLE SHOOTING - NO CODES - 4.3L SIERRA & SILVERADO article.

FUEL INJECTOR BALANCE TEST WITH TECH 2

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

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158208-S20709970632003091700000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Perform «FUEL INJECTOR COIL TEST»(ref-153194-S21564381642003032400000) . 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 PRESSURE TEST»(ref-152743-S07134794452003022400000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO 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 PRESSURE TEST»(ref-152743-S07134794452003022400000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO 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-152982-S33481225962003030700000) in TROUBLE SHOOTING - NO CODES - 4.3L SIERRA & SILVERADO 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-152982-S33481225962003030700000) in TROUBLE SHOOTING - NO CODES - 4.3L SIERRA & SILVERADO 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 SIERRA & SILVERADO article.

FUEL INJECTOR COIL TEST

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

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-158208-S20709970632003091700000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO 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-153194-S19773483622003032400000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(ref-153194-S24097502032003032400000) . 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-153194-S19773483622003032400000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(ref-153194-S24097502032003032400000) . 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 20

Scheme 21

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-158208-S20709970632003091700000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO 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 20) 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 21) 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 21) 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 «REMOVAL & INSTALLATION - SIERRA & SILVERADO - FLEX-FUEL & GASOLINE»(ref-157348) 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 TEST under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO 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-158208-S20709970632003091700000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO 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-153194-S25415670202003032400000) .
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 component locations, see COMPONENT LOCATIONS . For circuit reference, see WIRING DIAGRAMS .

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-152982-S26766645902003030700000) in TROUBLE SHOOTING - NO CODES - 4.3L SIERRA & SILVERADO article.

1. Perform Diagnostic System Check - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158208-S20709970632003091700000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO 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-153194-S05322076372003032400000). If no, go to next step.
3. Turn ignition off. Disconnect 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 22) 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 «REMOVAL & INSTALLATION - SIERRA & SILVERADO - FLEX-FUEL & GASOLINE»(ref-157348) 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-158208-S06912544392003091700000) in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article. If no, system is okay.

Scheme 22

ELECTRONIC IGNITION SYSTEM DIAGNOSIS

See DISTRIBUTOR IGNITION SYSTEM under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO article.

EVAP Control System Diagnosis

For EVAP control system diagnosis, see INSPECTION/MAINTENANCE EVAPORATIVE EMISSION SET PROCEDURE under DRIVE CYCLES in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article.