Engine Controls - System & Component Testing - 8.1L: Diagnosis Chevrolet Silverado 1500 HD

ALCOHOL/CONTAMINANTS IN FUEL DIAGNOSIS WITH SPECIAL TOOL

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

Diagnostic Procedures

1. Test the fuel composition using the Fuel Composition Tester (J-44175) and Instruction Manual (J-44175-3).
2. If water appears in the fuel sample, clean the fuel system. See «FUEL SYSTEM CLEANING»(ref-153339-S25204608442003040200000) and replace fuel filter.
3. Subtract 50 from the reading on the DVOM in order to obtain the percentage of alcohol in the fuel sample.
4. If 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 fuel in the vehicle. See «FUEL SYSTEM CLEANING»(ref-153339-S25204608442003040200000) .

ALCOHOL/CONTAMINANTS IN FUEL DIAGNOSIS WITHOUT SPECIAL TOOL

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

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-153339-S25204608442003040200000) .

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-158433-S21464854222003092600000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Perform «FUEL INJECTOR COIL TEST»(ref-153339-S13092179522003040200000). 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-152876-S29682748142003030100000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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-152876-S29682748142003030100000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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-153006-S25129811232003031000000) in TROUBLE SHOOTING - NO CODES - 8.1L AVALANCHE, SILVERADO, SUBURBAN & YUKON XL 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-153006-S25129811232003031000000) in TROUBLE SHOOTING - NO CODES - 8.1L AVALANCHE, SILVERADO, SUBURBAN & YUKON XL 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-158433-S21464854222003092600000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. After performing Diagnostic System Check - Engine Controls, go to next step.
2. Perform «FUEL INJECTOR COIL TEST»(ref-153339-S13092179522003040200000) . After performing Fuel Injector Coil Test, go to next step.
3. Turn ignition and all accessories off. Install fuel pressure gauge. Turn ignition on, with engine off. Using scan tool, command fuel pump on. You may need to command the fuel pump ON a few times in order to obtain the highest possible fuel pressure. DO NOT start engine. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure 55-62 psi (385-425 kPa)? If yes, go to next step. If no, diagnose fuel system.
4. Observe fuel pressure gauge for one minute. Does the fuel pressure drop more than 5 psi (34 kPa)? If yes, diagnose fuel system. If no, go to next step.
5. Using 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-153006-S25129811232003031000000) in TROUBLE SHOOTING - NO CODES - 8.1L AVALANCHE, SILVERADO, SUBURBAN & YUKON XL article.
6. Replace affected fuel injectors. 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 «SYMPTOMS»(ref-153006-S25129811232003031000000) in TROUBLE SHOOTING - NO CODES - 8.1L AVALANCHE, SILVERADO, SUBURBAN & YUKON XL 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 - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.

FUEL INJECTOR COIL TEST

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

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-158433-S21464854222003092600000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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-153339-S35551757132003040200000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(ref-153339-S03980260292003040200000) . 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-153339-S35551757132003040200000) or «FUEL INJECTOR BALANCE TEST WITH TECH 2»(ref-153339-S03980260292003040200000) . 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 95

Scheme 96

When the ignition is turned on, the PCM will turn on the in-tank fuel pump. The in-tank fuel pump will remain on as long as the engine is cranking or running and PCM is receiving reference pulses. If there are no reference pulses, PCM will turn the in-tank fuel pump off 2 seconds after ignition is turned on or 2 seconds after engine stops running.

The following conditions may have caused fuel pump fuse to open: A faulty fuse, intermittent short in fuel pump power supply circuit or an intermittent internal component failure.

1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158433-S21464854222003092600000) under SELF DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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. See «DIAGNOSTIC AIDS»(ref-153339-S14543460032003041600000). 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 95) 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 96) 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 21.
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 96) 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 19.
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. Inspect for poor connections at the fuel pump. Did you find and correct the condition? If yes, go to step 27. If no, go to step 24.
19. Test for 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. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 27. If no, go to step 26.
21. Repair the supply voltage circuit of the fuel pump for a short to voltage. After repairs, go to step 27.
22. Repair open in fuel pump relay ground circuit. After repairs, go to step 27.
23. Repair the battery voltage circuit of the fuel pump relay switch. After repairs, go to step 27.
24. Replace fuel pump. After replacing fuel pump, go to step 27.
25. Replace fuel pump relay. After replacing relay, go to step 27.
26. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Reprogram ECM. 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 - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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-158433-S21464854222003092600000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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-153339-S11701853722003040200000) .
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 .

ELECTRONIC IGNITION SYSTEM DIAGNOSIS

See ELECTRONIC IGNITION SYSTEM under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.

The ignition relay is a normally open relay. The relay armature is held in open position by spring tension. When ignition switch is turned to run or start position, current will flow through relay coil. A wire connected to other end of relay coil completes path to ground. The electromagnetic field created by relay coil, overcomes spring tension and moves armature allowing relay contacts to close. The closed relay contacts allow current to flow from battery to following fuses: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA fuse, if equipped.

When ignition switch is turned off, electromagnetic field collapses. This action allows spring tension to move armature away from relay contacts, which interrupts current flow to fuses. If ignition relay fails to close, engine will crank, but will not run. The class 2 communications will be available with use of a scan tool.

1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-158433-S21464854222003092600000) under SELF DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. After performing diagnostic system check, go to next step.
2. Turn ignition on, with engine off. Remove underhood fuse/relay block cover. Probe following fuses with a test light connected to a good ground: PCM 1, ETC/ECM, INJ 1, INJ 2, and SBA fuse, if equipped. (Scheme 95) 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 PCM 1 fuse with a test light connected to a good ground. Does test light illuminate on either test point of fuse? If yes, go to next step. If no, go to step 30.
4. Turn ignition off. Remove ignition relay from underhood fuse/relay block. Probe ignition 1 voltage circuit of ignition relay at 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 relay load bus bar of underhood fuse/relay block between ignition relay and fuses to 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 following fuses from underhood fuse/relay block: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA fuse, if equipped. Probe fuse terminals in underhood fuse/relay block with a test light that is connected to a good ground. Does test light illuminate at any of 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 ignition 1 voltage circuit for ignition relay. Disconnect ignition switch electrical connector that contains ignition 1 voltage circuit for ignition relay. Reconnect negative battery cable. Test ignition 1 voltage circuit for a short to battery positive voltage. Did you find and correct 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 ignition switch electrical connector with a test light connected to a good ground. Does test light illuminate? If yes, go to step 28. If no, go to next step.
9. Test ignition 1 voltage bus bar circuit in 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 40-amp IGN "B" fuse in underhood fuse/relay block. Is fuse open? If yes, go to next step. If no, go to step 18.
11. Remove 40-amp IGN "B" fuse from underhood fuse/relay block. Probe both fuse terminals in underhood fuse/relay block with a test light that is connected to a good ground. Does test light illuminate on at least one fuse terminal? If yes, go to next step. If no, go to step 17.
12. Test ignition 1 voltage circuit between ignition switch and underhood fuse/relay block for a short to ground. Did you find and correct condition? If yes, go to step 30. If no, go to next step.
13. Test 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 battery positive voltage circuit between underhood fuse/relay block and ignition switch for a short to ground. Did you find and correct condition? If yes, go to step 30. If no, go to next step.
15. Test battery positive voltage bus bar circuit of underhood fuse/relay block between 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 ignition 1 voltage bus bar circuit of underhood fuse/relay block that contains 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 mounting stud for battery positive cable at underhood fuse/relay block with a test light connected to a good ground. Does 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 battery positive voltage circuit of ignition relay at 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 ignition 1 voltage circuit of ignition relay at underhood fuse/relay block with a test light connected to a good ground. Does test light illuminate? If yes, go to step 23. If no, go to next step.
20. Turn ignition off. Test ignition 1 voltage circuit between ignition switch and underhood fuse/relay block for a high resistance or for an open. Did you find and correct condition? If yes, go to step 30. If no, go to next step.
21. Test 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 battery positive voltage circuit between ignition switch and underhood fuse/relay block for a high resistance or for an open. Did you find and correct condition? If yes, go to step 30. If no, go to step 29.
23. Turn ignition on, with engine off. Probe coil ground circuit of ignition relay at 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 underhood fuse/relay block electrical connectors. Test coil ground circuit of ignition relay at underhood fuse/relay block electrical connector for a high resistance or for an open. Did you find and correct condition? If yes, go to step 30. If no, go to step 29.
25. Turn ignition off. Jumper ignition relay battery positive voltage circuit and ignition relay load circuit together at underhood fuse/relay block with a 20-amp fused jumper wire. Probe following fuses with a test light that is connected to a good ground: PCM 1, ETC/ECM, INJ 1, INJ 2 and SBA fuse, if equipped. Does 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 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 engine. Does engine start and run? If yes, go to next step. If no, go to «NO-START - ENGINE CRANKS OKAY»(ref-152876-S27765079352003030100000) under NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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-158433-S36149293242003092600000) in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. If no DTC(s) are set, system is okay.

EVAP Control System Diagnosis

For EVAP control system diagnosis, see appropriate INSPECTION/MAINTENANCE PROCEDURES under DRIVE CYCLES in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.