Engine Controls - Basic Diagnostic Procedures - 8.1L: Overview Chevrolet Silverado 1500 HD

System Description

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

The in-tank fuel pump is an electric pump attached to the fuel sender assembly. The fuel pump is designed to provide fuel at a pressure above the pressure needed by the fuel injectors. A fuel pressure regulator, attached to the fuel rail, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate fuel return pipe.

Test Description

The numbers below refer to step numbers on diagnostic procedure.

1. 2 - This step verifies that the fuel pump is operating.
2. 4 - This step tests for an internal fuel leak. If the fuel pressure drops during this test, then an internal loss of pressure is indicated.
3. 6 - This step tests the fuel pressure regulator. The fuel pressure regulator is controlled by engine vacuum. With engine vacuum applied, the pressure should drop the specified value.
4. 9 - This step inspects the fuel pressure regulator for a fuel leak from the vacuum port. If fuel leaks from the fuel pressure regulator while the fuel pump is commanded ON, replace the fuel pressure regulator.
5. 10 - This step tests for a loss of fuel pressure between the fuel feed pipe shut-off adapter and the fuel pump.
6. 11 - This step tests for a leaking fuel injector, or fuel pressure regulator. If the fuel pressure remains constant during this test, the fuel injectors are not leaking fuel.
7. 14 - This step tests for a restricted fuel return pipe. If the fuel pressure is within the specified values, a restriction in the fuel return pipe is indicated.
8. 16 - This step determines if the fuel pressure regulator or the fuel pump is the cause of the low fuel pressure. If pressure rises above the specified value, the fuel pump is okay.
9. 18 - This step verifies that a circuit condition is not the cause of a fuel pressure concern. Inspect all fuel pump electrical circuits thoroughly.

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. Command fuel pump relay on with a scan tool. Does fuel pump operate? If yes, go to next step. If no, go to «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(ref-153339-S42480524892003041600000) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
3. Verify that adequate fuel is in fuel tank before proceeding with this diagnostic. Turn ignition off. Turn off all accessories. Install fuel pressure gauge. Turn ignition on, with engine off. Fuel pump relay may need to be commanded on a few times in order to obtain highest possible fuel pressure. Do not start engine. Command fuel pump relay on with a scan tool. Observe fuel pressure gauge with fuel pump commanded on. Is fuel pressure within 55-62 psi (379-427 kPa)? If yes, go to next step. If no, go to step 12 .
4. Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to step 8 . If no, go to next step.
5. Release fuel pressure to 10 psi (69 kPa). Monitor fuel pressure gauge for 5 minutes. Does fuel pressure decrease by more than 2 psi (14 kPa)? If yes, go to step 22 . If no, go to next step.
6. Turn ignition on, with engine off. Monitor fuel pressure gauge. Start engine. Does fuel pressure decrease by 3-10 psi (21-69 kPa) when engine is started? If yes, go to next step. If no, go to step 8 .
7. Operate vehicle within conditions to reproduce original symptoms. Monitor O2 and fuel trim parameters with a scan tool. Do any of scan tool parameters indicate a lean condition? If yes, go to step 17 . If no, problem is intermittent. See «INTERMITTENTS»(ref-153006-S08852526352003031000000) in TROUBLE SHOOTING - NO CODES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
8. Disconnect vacuum hose from fuel pressure regulator. Monitor fuel pressure gauge. Idle engine. Apply 12-14 inches of vacuum to fuel pressure regulator with a hand-held vacuum pump. Does fuel pressure drop 3-10 psi (21-69 kPa) when vacuum is applied? If yes, go to step 21 . If no, go to step 23 .
9. Turn ignition off. Disconnect vacuum hose from fuel pressure regulator. Turn ignition on, with engine off. Command fuel pump ON with a scan tool. Inspect for a fuel leak from vacuum port of fuel pressure regulator . Is fuel pressure regulator leaking fuel? If yes, go to step 23 . If no, go to next step.
10. Turn ignition off. Release fuel pressure. Disconnect fuel feed hose and fuel return hose from fuel rail. Install Fuel Line Shut-Off Adapters (J-37287) between fuel hoses and fuel rail pipes. Open valves on fuel pipe shut-off adapters. Turn ignition on, with engine off. Command fuel pump ON with a scan tool. Bleed air from fuel pressure gauge. Command fuel pump ON and OFF with a scan tool. Close fuel feed pipe shut-off valve. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step 19 . If no, go to next step.
11. Turn ignition off. Open shut-off valve for fuel feed pipe. Turn ignition on, with engine off. Command fuel pump ON and OFF with a scan tool. Close shut-off valve for fuel return pipe. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step 23 . If no, go to step 20 .
12. Is fuel pressure more than 62 psi (427 kPa)? If yes, go to step 14 . If no, go to next step.
13. Is fuel pressure more than zero psi? If yes, go to step 16 . If no, go to step 17 .
14. Turn ignition off. Release fuel pressure. Disconnect fuel return hose from fuel rail return pipe. Attach a length of flexible hose to fuel rail return pipe. Place open end of flexible fuel hose into an approved gasoline container. Turn ignition on, with engine off. Monitor fuel pressure gauge while fuel pump is operating. Is fuel pressure within 55-62 psi (379-427 kPa)? If yes, go to step 22 . If no, go to next step.
15. Inspect fuel rail outlet passage and fuel rail return pipe for a restriction. Did you find and correct condition? If yes, go to step 25 . If no, go to step 23 .
16. Turn ignition off. Release fuel pressure. Disconnect fuel return hose from fuel rail return pipe. Install Fuel Line Shut-Off Adapter (J-37287) between fuel return pipe and fuel rail. Open valve in fuel pipe shut-off adapter. Turn ignition on, with engine off. Bleed air from fuel pressure gauge. Monitor fuel pressure gauge. DO NOT allow fuel pressure to exceed 62 psi (427 kPa). Excessive pressure may damage fuel system. Command fuel pump relay on with a scan tool. Slowly close valve in fuel return pipe shut-off adapter, while fuel pump is operating. Does fuel pressure increase to more than 62 psi (427 kPa)? If yes, go to step 23 . If no, go to next step.
17. Inspect for restricted fuel filter or fuel feed pipe. Did you find and correct condition? If yes, go to step 25 . If no, go to next step.
18. Inspect harness connectors and ground circuits of fuel pump for poor connections. Did you find and correct condition? If yes, go to step 25 . If no, go to next step.
19. Remove fuel sender assembly. Inspect fuel pump flex hose for damage, in-tank fuel pump harness connectors for poor connections, fuel strainer for a restriction and fuel tank for contaminants. Did you find and correct condition? If yes, go to step 25 . If no, go to step 24 .
20. Turn ignition off. Raise fuel rail with fuel lines connected. Turn ignition on, with engine off. Command fuel pump relay ON with scan tool. Locate and replace leaking fuel injector. After repairs, go to step 25 .
21. Repair vacuum source to fuel pressure regulator. After repairs, go to step 25 .
22. Repair restricted fuel return pipe. After repairs, go to step 25 .
23. Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step 25 .
24. Replace fuel pump. After replacing fuel pump, go to next step.
25. Operate system in order to verify repair. Did you correct condition? If yes, system is okay. If no, go to step 3 .

The number below refers to step number on diagnostic procedure.

1. 5 - Monitoring misfire current counters determines if a fault is present.
2. 12 - A good indication that fuse is open is all off misfire current counters are incrementing on one side of engine. Inspect ignition positive voltage circuit for a grounded circuit. If fuse is open and ignition coil circuits are okay, inspect injector circuits for being grounded.

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. Crank engine. Observe engine speed parameter with a scan tool. Does scan tool display engine RPM? If yes, go to next step. If no, go to step 16.
3. Is DTC P0335, P0336 or P0351-P0358 also set? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-158433-S36149293242003092600000) in SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article. If DTC P0335, P0336 or P0351-P0358 are not set, go to next step.
4. Attempt to start engine. Does engine start and run? If yes, go to next step. If no, go to step 9.
5. Idle engine. Observe misfire current counters on scan tool. Does scan tool display any misfire current counters incrementing? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(ref-152876-S25549233482003030100000).
6. Do misfire current counters increment for most cylinders on one bank of engine? If yes, go to step 12. If no, go to next step.
7. Inspect spark plug wire for open circuits, cracks, or improper seating of terminals at spark plug or coil before proceeding with test. Inspect for spark at spark plug using Spark Tester (J-26792) while cranking. A few sparks, then nothing is considered no spark. Is adequate spark present? If yes, go to step 33. If no, go to next step.
8. Measure spark plug wire resistance. Is resistance more than 1000 ohms per foot? If yes, go to step 32. If no, go to next step.
9. Turn ignition off. Disconnect ignition coil that corresponds to Misfire Current counter that was incrementing. Turn ignition on, with engine off. Probe ignition 1 voltage circuit of ignition coil with a test light connected to a good ground. (Схема №3)or (Схема №4). Does test light illuminate? If yes, go to next step. If no, go to step 13.
10. Probe ignition 1 voltage circuit at ignition coil with a test light connected to ground circuit of ignition coil. Does test light illuminate? If yes, go to next step. If no, go to step 14.
11. Probe ignition 1 voltage circuit at ignition coil with a test light connected to low reference circuit of ignition coil. Does test light illuminate? If yes, go to step 20. If no, go to step 15.
12. Inspect for an open INJ "A" or INJ "B" fuse. Is fuse open? If yes, go to step 29. If no, go to step 23.
13. Disconnect main ignition coil 8-way connector. Probe ignition 1 voltage circuit at ignition coil main 8-way connector using test light connected to battery ground. Does test light illuminate? If yes, go to step 24. If no, go to step 23.
14. Disconnect main ignition coil 8-way connector. Probe ignition 1 voltage circuit on harness side with a test light connected to ground circuit of ignition coil. Does test light illuminate? If yes, go to step 18. If no, go to step 26.
15. Disconnect main ignition coil 8-way connector. Probe ignition 1 voltage circuit on harness side with a test light connected to low reference circuit of ignition coil. Does test light illuminate? If yes, go to step 19. If no, go to step 28.
16. Turn ignition on, with engine off. Disconnect CKP sensor. (Схема №2) Measure voltage from CKP sensor 12-volt reference circuit and a good ground with DVOM. (Схема №5) Compare measured voltage with system voltage. Is difference in voltage more than 0.5 volt? If yes, go to next step. If no, go to step 30.
17. Test for a short to ground in CKP 12-volt reference circuit or CMP sensor 12-volt reference circuit. (Схема №1), (Схема №2) or (Схема №5). Did you find and correct condition? If yes, go to step 35. If no, go to step 22.
18. Test for an intermittent and for a poor connection at ignition coil 8-way connector. Did you find and correct condition? If yes, go to step 35. If no, go to step 25.
19. Test for an intermittent and for a poor connection at ignition coil 8-way connector. Did you find and correct condition? If yes, go to step 35. If no, go to step 27.
20. Test for an intermittent and for a poor connection at ignition coil. Did you find and correct condition? If yes, go to step 35. If no, go to step 31.
21. Test for an intermittent and for a poor connection at CKP sensor. Did you find and correct condition? If yes, go to step 35. If no, go to step 30.
22. Test for an intermittent and for a poor connection at PCM. Did you find and correct condition? If yes, go to step 35. If no, go to step 34.
23. Repair open or high resistance in ignition 1 voltage circuit between fuse block and splice. After repairs, go to step 35.
24. Repair open or high resistance in ignition 1 voltage circuit between splice and ignition coil connector. After repairs, go to step 35.
25. Repair open in ground circuit between main 8-way connector and ignition coil. After repairs, go to step 35.
26. Repair open in ground circuit. After repairs, go to step 35.
27. Repair open in low reference circuit between main 8-way connector and ignition coil. After repairs, go to step 35.
28. Repair open in low reference circuit between PCM and splice. After repairs, go to step 35.
29. Repair ignition 1 voltage for a short to ground. Replace fuse. After repairs, go to step 35.
30. Replace CKP sensor. After replacing sensor, go to step 35.
31. Replace ignition coil. After replacing ignition coil, go to step 35.
32. Replace spark plug wire. After replacing spark plug wire, go to step 35.
33. Replace spark plug. After replacing spark plug, go to step 35.
34. Replace PCM. See appropriate REMOVAL & INSTALLATION article. After replacing PCM, go to next step.
35. Attempt to start engine. Does engine start and continue to run? If yes, go to next step. If no, go to step 2.
36. Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Let engine reach operating temperature. Are there 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.