Engine Controls - Basic Diagnostic Procedures: Overview Chevrolet TrailBlazer I

Test Description

The numbers below refer to step numbers in diagnostic procedure.

1. 8 - The Crankshaft Position (CKP) sensor can fail in such a way that will cause engine to crank but will not run. The engine will be able to run by using cam sensor when CKP sensor is disconnected.

1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK -- ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM in SELF DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After performing diagnostic system check, go to next step.
2. Using scan tool, check for DTCs. If DTCs P0107, P0601, P0602, P0604, P0606, P0607, P1220, P1221, P1271, P1514, P1621, P1631, P1635, P1639, P1680, P1681 or P1683 are set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If DTCs are not set, go to next step.
3. Monitor Ignition 1 Signal Voltage parameter with a scan tool. Is ignition 1 signal voltage parameter at battery voltage? If yes, go to next step. If no, go to step 10.
4. Command fuel pump on with a scan tool. Does fuel pump turn on? If yes, go to next step. If no, go to «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(ref-153168-S23811791912003041400000) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
5. Turn ignition off. Remove an ignition coil. Install Spark Tester (J-26792) to coil boot. Attempt to start engine. Does spark tester spark? If yes, go to next step. If no, diagnose electronic ignition system. Go to «ELECTRONIC IGNITION SYSTEM»(ref-152692-S20375326552003021900000).
6. Turn ignition off. Disconnect fuel injector harness multi-way connector. Probe fuel injector control circuit, PCM side, with a test light connected to battery voltage. Crank engine. Does test light flash when cranking engine? If yes, go to next step. If no, diagnose fuel injector circuit. See «FUEL INJECTOR CIRCUIT DIAGNOSIS»(ref-153168-S25175604842003032100000) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
7. Turn ignition off. Install Fuel Pressure Gauge (J-34730-1A). Turn ignition on, with engine off. Command fuel pump on with a scan tool. Is fuel pressure within 48-52 psi (334-375 kPa) while fuel pump is operating? If yes, go to next step. If no, go to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000).
8. Disconnect Crankshaft Position (CKP) sensor. CKP sensor is located on left rear of engine block. (Схема №1) Attempt to start engine. Does engine start and continue to run? If yes, go to step 11. If no, go to next step.
9. Inspect for collapsed air intake duct, restricted air filter element, fouled spark plugs, engine mechanical problem or restricted exhaust system. Check if ECT sensor is NOT close to actual engine temperature. Compare MAP/BARO parameters to another vehicle. The parameters should be close in value. Check for TP sensor being stuck in range. Repair as necessary. After repairs, go to step 12.
10. Repair ignition 1 signal voltage circuit for an open or a short to ground. Replace fuse, if necessary. After repairs, go to next step.
11. Replace CKP sensor. After replacing sensor, go to next step. If no, go to step 2.
12. Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Attempt to start engine. Does engine start and continue to run? If yes, go to next step. If no, go to step 2.
13. Allow engine to reach operating temperature. Observe DTC information 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-155898-S19906497452003062800000) in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no DTCs are set, system is okay.

System Description

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.

The fuel tank stores fuel supply. The fuel pump supplies fuel through an in line fuel filter to fuel injection system. The pump provides fuel at a higher rate of flow than is needed by fuel injection system. The fuel pressure regulator maintains correct fuel pressure to fuel injection system. A separate pipe returns unused fuel to fuel tank.

1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK -- ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF DIAGNOSTIC SYSTEM in SELF DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT 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-153168-S23811791912003041400000) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT 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 48-54 psi (334-375 kPa)? If yes, go to next step. If no, go to step 10 .
4. Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to step 7 . If no, go to next step.
5. Relieve 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 21 . If no, go to next step.
6. 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 15 . If no, see «INTERMITTENTS»(ref-152936-S40530116252003030500000) in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
7. Turn ignition off. Remove vent hose from fuel pressure regulator. Turn ignition on, with engine off. Command fuel pump relay on with a scan tool. Inspect for a fuel leak from fuel pressure regulator atmospheric vent. Is fuel pressure regulator leaking fuel? If yes, go to step 20 . If no, go to next step.
8. Turn ignition off. Relieve fuel pressure. Disconnect fuel feed hose and fuel return hose from fuel rail pipes. 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 relay on with a scan tool. Bleed air from fuel pressure gauge. Command fuel pump relay on and then 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 17 . If no, go to next step.
9. Turn ignition off. Open fuel feed pipe shut-off valve. Turn ignition on, with engine off. Command fuel pump relay on and then off with a scan tool. Close fuel return pipe shut-off valve. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step 20 . If no, go to step 18 .
10. Is fuel pressure more than 54 psi (375 kPa)? If yes, go to step 12 . If no, go to next step.
11. Is fuel pressure more than zero psi? If yes, go to step 14 . If no, go to step 15 .
12. Turn ignition off. Relieve 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 48-54 psi (334-375 kPa)? If yes, go to step 19 . If no, go to next step.
13. Inspect fuel rail outlet passage and fuel rail return pipe for a restriction. Did you find and correct condition? If yes, go to step 22 . If no, go to step 20 .
14. Turn ignition off. Relieve 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 75 psi (517 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 54 psi (375 kPa)? If yes, go to step 20 . If no, go to next step.
15. Inspect for restricted fuel filter or fuel feed pipe. Did you find and correct condition? If yes, go to step 22 . If no, go to next step.
16. Inspect harness connectors and ground circuits of fuel pump for poor connections. Did you find and correct condition? If yes, go to step 22 . If no, go to next step.
17. 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 22 . If no, go to step 21 .
18. Turn ignition off. Raise fuel rail with fuel pipes connected. Turn ignition on, with engine off. Command fuel pump relay on with a scan tool. Locate and replace leaking fuel injector. After repairs, go to step 22 .
19. Repair restricted fuel return pipe. After repairs, go to step 22 .
20. Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step 22 .
21. Replace fuel sender. After replacing fuel sender, go to next step.
22. 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 - A few sparks, then nothing is considered no spark.

1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK -- ENGINE CONTROLS»(ref-155898-S30062612662003062800000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After performing diagnostic system check, go to next step.
2. Are DTCs P0335 or P0336 set? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no DTC(s) are set, go to next step.
3. Attempt to start engine. Does engine start and run? If yes, go to next step. If no, go to step 15.
4. Observe Misfire Current Counters parameter with a scan tool. Does scan tool display any Misfire Current Counters incrementing? If yes, go to next step. If no, see «DIAGNOSTIC AIDS»(ref-152692-S16434393152003021900000).
5. Remove ignition coil for affected cylinder. Install Spark Tester (J-26792) to spark plug boot. Attach tester to a good engine ground. Observe spark tester. Crank engine. Does spark jump tester gap? If yes, go to step 11. If no, go to next step.
6. Turn ignition off. Disconnect ignition coil for misfiring cylinder. Turn ignition on, with engine off. Probe ignition 1 voltage circuit of affected ignition coil with a test light connected to good ground. (Схема №3) Does test light illuminate? If yes, go to next step. If no, go to step 15.
7. Probe ignition 1 voltage circuit of affected ignition coil with a test light connected to ignition coil ground circuit. Does test light illuminate? If yes, go to next step. If no, go to step 16.
8. Start engine. Measure frequency from IC control circuit of respective ignition coil to a good ground. Does frequency measure within 2-20 Hz? If yes, go to step 14. If no, go to next step.
9. Turn on ignition, with engine off. Measure voltage from IC control circuit of respective ignition coil to a good ground with a DVOM. Does voltage measure more than one volt? If yes, go to step 17. If no, go to next step.
10. Test IC control circuit for an open, short to ground or high resistance. Did you find and correct condition? If yes, go to step 21. If no, go to step 13.
11. Exchange spark plug with a spark plug from a non misfiring cylinder. Install ignition coil. Start engine. Does scan tool display that misfire followed that spark plug? If yes, go to step 20. If no, go to next step.
12. Inspect insulating spark plug boot and conducting spring for any contamination, deterioration or arching. Did you find and correct condition? If yes, go to step 21. If no, diagnose for an engine mechanical problem.
13. Test for an intermittent and for a poor connection at PCM. Did you find and correct condition? If yes, go to step 21. If no, go to step 19.
14. Test for an intermittent and for a poor connection at ignition coil. Did you find and correct condition? If yes, go to step 21. If no, go to step 18.
15. Repair open or short to ground in ignition 1 voltage circuit. (Схема №3) After repairs, go to step 21.
16. Repair open in ignition coil ground circuit. After repairs, go to step 21.
17. Repair short to voltage in IC control circuit. After repairs, go to step 21.
18. Replace ignition coil. After replacing ignition coil, go to step 21.
19. Replace PCM. Refer to «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article. After replacing PCM, go to step 21.
20. Replace spark plug. After replacing spark plug, go to next step.
21. Start engine. Does engine start and run? If yes, go to next step. If no, go to step 2.
22. 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-155898-S19906497452003062800000) in SELF DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no DTC(s) are set, system is okay.