Engine Controls - Basic Diagnostic Procedures: Other Chevrolet Venture I

Compression

Check engine mechanical condition with compression gauge, vacuum gauge, or engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, see appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use vacuum gauge or low-pressure (0-5 psi) gauge to check exhaust system.

If vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Partially open throttle and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for restriction. If using low pressure gauge, connect gauge in the following manner

1. Check At Oxygen Sensor Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.

NO START - ENGINE CRANKS OKAY (2.2L)

Note. Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

Ignition System

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Using scan tool, check for DTCs. If DTC P0601, P0602, P1621, P1626, P1631 or P1632 is set, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If DTCs are not set, go to next step.
3. Using scan tool, monitor CKP activity counter while cranking engine. If counter increments, go to next step. If counter does not increment, go to step 8 .
4. Using scan tool, command fuel pump on. If fuel pump runs, go to next step. If fuel pump does not run, diagnose fuel pump electrical circuit. See «FUEL PUMP ELECTRICAL CIRCUIT»(ref-3909-S01037385962000052300000) .
5. Connect fuel pressure gauge. See «BASIC FUEL SYSTEM CHECKS (GASOLINE)»(ref-3909-S32232778352000052300000) . Using scan tool, command fuel pump on. If fuel pressure is 41-47 psi (2.9-3.3 kg/cm 2 ), go to next step. If fuel pressure is not as specified, diagnose fuel system. See «BASIC FUEL SYSTEM CHECKS (GASOLINE)»(ref-3909-S32232778352000052300000) .
6. Connect Spark Tester (J-26792) to No. 1 spark plug wire. Leave other wires connected. Crank engine and check for spark. Repeat for each cylinder. If spark was present at all cylinders, go to next step. If spark was not present at all cylinders, go to step 12 .
7. Turn ignition off. Check for faulty spark plugs. Repair as necessary. After repairs, go to step 24 . If spark plugs are okay, see «DIAGNOSTIC AIDS»(ref-3909-S14657651922000061500000) .
8. Turn ignition off. Disconnect 2-pin ignition control module harness connector. Turn ignition on. Measure voltage between 2-pin harness connector terminals. If battery voltage is present, go to next step. If battery voltage is not present, go to step 19 .
9. Disconnect 6-pin ignition control module harness connector. Measure resistance between CKP sensor signal circuit and CKP sensor ground circuit at 6-pin harness connector. If resistance is 700-1300 ohms, leave DVOM connected and go to next step. If resistance is not 700-1300 ohms, go to step 15 .
10. Set DVOM to AC scale. Crank engine while monitoring DVOM. If AC voltage is greater than 200 millivolts, go to next step. If AC voltage is not greater than 200 millivolts, go to step 21 .
11. Using test light connected to battery voltage, momentarily probe CKP 7X reference signal circuit, and then ignition control module reference low circuit at 6-pin ignition control module harness connector. Using scan tool, monitor CKP activity counter. If counter increments, go to step 14 . If counter does not increment, go to step 16 .
12. Measure resistance of each spark plug wire. If resistance is less than 30,000 ohms, go to next step. If resistance is not less than 30,000 ohms, go to step 20 .
13. Turn ignition off. Disconnect 6-pin ignition control module harness connector. Measure voltage between battery voltage and affected coil ignition control circuit at 6-pin harness connector. If battery voltage is present, go to step 17 . If battery voltage is not present, go to step 18 .
14. Check 6-pin ignition control module harness connector for poor connections. Repair as necessary. After repairs, go to step 24 . If connections are okay, go to step 22 .
15. Check CKP sensor ground circuit for poor connection, open, short to ground or short to voltage. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 21 .
16. Check CKP sensor signal circuit for poor connection, open, short to ground or short to voltage. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 23 .
17. Check coil ignition control circuit for open or poor connection at ignition control module. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 22 .
18. Check coil ignition control circuit for open or poor connection at PCM. Repair as necessary. After repairs, go to step 24 . If circuit is okay, go to step 22 .
19. Repair open in ignition control module ground circuit or ignition feed circuit. After repairs, go to step 24 .
20. Replace faulty spark plugs. After repairs, go to step 24 .
21. Replace CKP sensor. Perform crankshaft position system variation learn procedure. After repairs, go to step 24 .
22. Replace ignition control module. After repairs, go to step 24 .
23. Replace PCM. Perform PCM relearn procedures. After repairs, go to next step.
24. Attempt to start engine. If engine starts and continues to run, perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. If engine does not start, go to step 2 .

Fuel Pump Electrical Circuit

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Connect scan tool. Turn ignition on. Using scan tool, command fuel pump relay on and off. If fuel pump turns on and off, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If fuel pump does not turn on and off, go to next step.
3. Using scan tool, command fuel pump relay on and off. If fuel pump relay clicks, go to step 9 . If fuel pump relay does not click, go to next step.
4. Turn ignition off. Disconnect fuel pump relay located in underhood fuse block. Turn ignition on. Using test light connected to ground, probe fuel pump relay control circuit at relay cavity. Using scan tool, command fuel pump relay on and off. If test light turns on and off, go to next step. If test light does not turn on and off, go to step 6 .
5. Connect test light between fuel pump relay control circuit and fuel pump relay ground circuit at relay cavities. Using scan tool, command fuel pump relay on and off. If test light turns on and off, go to step 19 . If test light does not turn on and off, go to step 22 .
6. If test light remains illuminated, go to next step. If test light does not remain illuminated, go to step 8 .
7. Disconnect PCM. Check fuel pump relay control circuit for short to voltage. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to step 26 .
8. Disconnect PCM. Check fuel pump relay control circuit for open or short to ground. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to step 20 .
9. Turn ignition on. If fuel pump runs continuously, go to next step. If fuel pump does not run continuously, go to step 11 .
10. Turn ignition off. Disconnect fuel pump relay located in underhood fuse block. Turn ignition on. If fuel pump runs continuously, go to step 21 . If fuel pump does not run continuously, go to step 25 .
11. Check ECM B fuse (20-amp) located in underhood fuse block. If fuse is open, go to next step. If fuse is okay, go to step 14 .
12. Check for short to ground in fuel pump power feed circuit between fuel pump and fuse. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
13. Reconnect all components. Install NEW ECM B fuse (20-amp). Using scan tool, command fuel pump on. If fuse blows, go to step 24 . If fuse does not blow, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article.
14. Turn ignition off. Disconnect fuel pump relay located in underhood fuse block. Turn ignition on. Using test light connected to ground, probe fuel pump relay battery feed circuit at fuel pump relay cavity. If test light illuminates, go to next step. If test light does not illuminate, go to step 23 .
15. Connect fused jumper wire between fuel pump relay battery feed circuit and fuel pump power feed circuit at fuel pump relay cavities. If fuel pump runs, go to step 19 . If fuel pump does not run, go to next step.
16. Check fuel pump power feed circuit for open or high resistance between fuel pump and fuel pump relay. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
17. Check fuel pump ground circuit for open or high resistance. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
18. Check for poor connections at fuel pump. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 24 .
19. Check for poor connections at fuel pump relay. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 25 .
20. Check for poor connections at PCM. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 26 .
21. Repair short to voltage in fuel pump power supply circuit. After repairs, go to step 27 .
22. Repair open in fuel pump relay ground circuit. After repairs, go to step 27 .
23. Repair fuel pump relay battery feed circuit. After repairs, go to step 27 .
24. Replace fuel pump. Replace ECM B fuse (20-amp) if necessary. After repairs, go to step 27 .
25. Replace fuel pump relay. After repairs, go to step 27 .
26. Replace PCM. Perform PCM relearn procedures. After repairs, go to next step.
27. Operate system and verify repair. If system operation is okay, testing is complete. If system operation is not okay, go to step 2 .

NO START - ENGINE CRANKS OKAY (3.4L)

Note. Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank. Perform OBD system check following any repairs. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Disconnect 24X CKP sensor. Using scan tool, monitor 3X reference parameter while cranking engine. If scan tool indicates 3X reference, go to next step. If scan tool does not indicate 3X reference, go to step 10 .
3. Reconnect 24X CKP sensor. Using Spark Tester (J-26792), check for spark at each cylinder. If any cylinders did not have spark, go to next step. If all cylinders have spark, go to step 7 .
4. Check spark plugs, spark plug wires and ignition coils for short to ground or carbon tracking. Repair as necessary. If no problem is found, go to next step.
5. Measure resistance of spark plug wires in question. Resistance should be no more than 600 ohms per foot. Repair as necessary. If spark plug wires are okay, go to next step.
6. Switch ignition coil in question with a known-good ignition coil. If fault follows ignition coil in question, replace ignition coil. If fault does not follow ignition coil in question, go to step 14 .
7. Check spark plug wires for correct routing and firing order. Repair as necessary. If no problem is found, go to next step.
8. Using DVOM, check spark plugs for internal short to ground. Repair as necessary. If spark plugs are okay, go to next step.
9. Replace faulty spark plugs.
10. Reconnect 24X CKP sensor. Disconnect 2-pin ignition control module harness connector. Turn ignition on. Using test light connected to ground, probe ignition control module ignition feed circuit at 2-pin harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 16 .
11. Connect test light between ignition control module ignition feed circuit and ignition control module ground circuit at 2-pin harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 19 .
12. Disconnect 7X CKP sensor harness connector from ignition control module. Using test light connected to battery voltage, probe 7X CKP sensor reference high and reference low circuits at ignition control module harness connector. If test light illuminates for either circuit, go to step 17 . If test light does not illuminate for either circuit, go to next step.
13. Using test light connected to ground, probe 7X CKP sensor reference high and reference low circuits at ignition control module harness connector. If test light illuminates for either circuit, go to step 18 . If test light does not illuminate for either circuit, go to next step.
14. Ensure battery voltage is within specification. Turn ignition off. Using DVOM set to measure AC duty cycle percent, connect leads between 7X CKP sensor reference high and reference low circuits at ignition control module harness connector. Crank engine. If DVOM indicates AC duty cycle, go to step 20 . If DVOM does not indicate AC duty cycle percent, go to next step.
15. Check 7X CKP sensor reference high and reference low circuits for opens or short together. Repair as necessary. If circuits are okay, go to step 21 .
16. Repair open or short to ground in ignition control module ignition feed circuit.
17. Repair short to ground in 7X reference circuit which illuminated test light.
18. Repair short to voltage in 7X reference circuit which illuminated test light.
19. Repair open in ignition control module ground circuit.
20. Replace ignition control module.
21. Replace 7X CKP sensor.

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Connect scan tool. Turn ignition on. Using scan tool, command fuel pump on and off. If fuel pump turns on and off, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If fuel pump does not turn on and off, go to next step.
3. Using scan tool, command fuel pump on and off. If fuel pump relay clicks, go to step 9 . If fuel pump relay does not click, go to next step.
4. Turn ignition off. Disconnect fuel pump relay located in underhood junction block. Turn ignition on. Using test light connected to ground, probe fuel pump relay control circuit at relay cavity. Using scan tool, command fuel pump on and off. If test light turns on and off, go to next step. If test light does not turn on and off, go to step 6 .
5. Connect test light between fuel pump relay control circuit and fuel pump relay ground circuit at relay cavities. Using scan tool, command fuel pump on and off. If test light turns on and off, go to step 21 . If test light does not turn on and off, go to step 24 .
6. If test light remains illuminated with each scan tool command, go to next step. If test light does not remain illuminated with each scan tool command, go to step 8 .
7. Disconnect PCM. Check fuel pump relay control circuit for short to voltage. Repair as necessary. After repairs, go to step 29 . If circuit is okay, go to step 28 .
8. Disconnect PCM. Check fuel pump relay control circuit for open or short to ground. Repair as necessary. After repairs, go to step 29 . If circuit is okay, go to step 22 .
9. Turn ignition on. If fuel pump runs continuously, go to next step. If fuel pump does not run continuously, go to step 11 .
10. Turn ignition off. Disconnect fuel pump relay located in underhood junction block. Turn ignition on. If fuel pump runs continuously, go to step 23 . If fuel pump does not run continuously, go to step 27 .
11. Check FUEL PUMP fuse (15-amp) located in underhood junction block. If fuse is open, go to next step. If fuse is okay, go to step 14 .
12. Disconnect in-line fuel pump harness connector located near fuel tank. Check for short to ground in fuel pump power feed circuit between fuel pump fuse and in-line fuel pump harness connector. Repair as necessary. After repairs, go to step 29 . If circuit is okay, go to next step.
13. Lower fuel tank. Check fuel pump harness for damage or grounded circuits. Repair as necessary. After repairs, go to step 29 . If fuel pump harness is okay, go to step 20 .
14. Turn ignition off. Disconnect fuel pump relay located in underhood junction block. Turn ignition on. Using test light connected to ground, probe fuel pump relay battery feed circuit at relay cavity. If test light illuminates, go to next step. If test light does not illuminate, go to step 25 .
15. Connect fused jumper wire between fuel pump relay battery feed circuit and fuel pump power feed circuit at relay cavities. If fuel pump runs, go to step 21 . If fuel pump does not run, go to next step.
16. Disconnect in-line fuel pump harness connector located near fuel tank. Check fuel pump power feed circuit for open or high resistance between fuel pump relay and in-line fuel pump harness connector. Repair as necessary. After repairs, go to step 29 . If circuit is okay, go to next step.
17. Check fuel pump ground circuit for open or high resistance between body pass-through connector and chassis ground. Repair as necessary. After repairs, go to step 29 . If circuit is okay, go to next step.
18. Check for poor connections at fuel pump in-line connector to body pass-through connector. Repair as necessary. After repairs, go to step 29 . If connections are okay, go to next step.
19. Lower fuel tank. Check fuel pump harness for damage or open circuits. Repair as necessary. After repairs, go to step 29 . If fuel pump harness is okay, go to step 26 .
20. Reconnect all components. Install NEW FUEL PUMP fuse (15-amp). Using scan tool, command fuel pump on. If fuse blows, go to step 26 . If fuse does not blow, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article.
21. Check for poor connections at fuel pump relay. Repair as necessary. After repairs, go to step 29 . If connections are okay, go to step 27 .
22. Check for poor connections at PCM. Repair as necessary. After repairs, go to step 29 . If connections are okay, go to step 28 .
23. Repair short to voltage in fuel pump power feed circuit. After repairs, go to step 29 .
24. Repair open in fuel pump relay ground circuit. After repairs, go to step 29 .
25. Repair open in fuel pump relay battery feed circuit. After repairs, go to step 29 .
26. Replace fuel pump. After repairs, go to step 29 .
27. Replace fuel pump relay. After repairs, go to step 29 .
28. Replace PCM. Perform PCM relearn procedures. After repairs, go to next step.
29. Operate system to verify repairs. If system operation is okay, testing is complete. If system operation is not okay, go to step 2 .

NO START - ENGINE CRANKS OKAY (4.3L, 5.0L, 5.7L & 7.4L)

Note. Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Check condition of spark plug wires. Replace if necessary. Using Spark Tester (J-26792), check for spark at spark plug wires while cranking engine. If spark is present, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If no spark is present, go to next step.
3. Remove coil wire from distributor cap. Check for spark at coil wire while cranking engine. If spark is present, go to step 13 . If spark is not present, go to next step.
4. Measure resistance of coil wire. If resistance is no greater than 1000 ohms per inch, go to next step. If resistance is greater than 1000 ohms per inch, go to step 32 .
5. Disconnect ignition coil harness connector. Using test light connected to battery voltage, probe ignition coil driver circuit at ignition coil harness connector. Crank engine. If test light flashes, go to step 7 . If test light does not flash, go to next step.
6. Turn ignition off. Using test light connected to battery voltage, probe ignition coil driver circuit at ignition coil harness connector. If test light illuminates, go to step 28 . If test light does not illuminate, go to step 9 .
7. Using test light connected to battery voltage, probe tachometer circuit at ignition coil harness connector. If test light illuminates, go to step 29 . If test light does not illuminate, go to next step.
8. Turn ignition on. Measure voltage between ground and ignition feed circuit at ignition coil harness connector. If voltage is greater than 10 volts, go to step 21 . If voltage is not greater than 10 volts, go to step 18 .
9. Turn ignition off. Disconnect ignition control module harness connector. Check for open in coil driver circuit between ignition control module and ignition coil. If circuit is open, go to step 27 . If circuit is okay, go to next step.
10. Turn ignition on. Measure voltage between ground and ignition feed circuit at ignition control module harness connector. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, go to step 19 .
11. Using test light connected to battery voltage, probe ignition control module ground circuit at ignition control module harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 23 .
12. Using DVOM set to AC scale, measure voltage between ground and ignition control module control circuit at ignition control module harness connector while cranking engine. If AC voltage is 1-4 volts, go to step 20 . If voltage is not 1-4 volts, go to step 15 .
13. Remove distributor cap. Check for cracks, moisture or carbon tracking. If a problem is found, go to step 34 . If distributor cap is okay, go to next step.
14. Crank engine and observe distributor rotor. If distributor rotor turns, go to step 33 . If distributor rotor does not turn, repair distributor or engine mechanical problem.
15. Turn ignition off. Disconnect VCM harness connector C3 (Clear). Check for open in ignition timing signal circuit between ignition control module and VCM. If circuit is open, go to step 24 . If circuit is okay, go to next step.
16. Using test light connected to battery voltage, probe ignition control module control circuit at VCM harness connector. If test light illuminates, go to step 25 . If test light does not illuminate, go to next step.
17. Turn ignition on. Using test light connected to ground, probe ignition control module control circuit at VCM harness connector. If test light illuminates, go to step 26 . If test light does not illuminate, go to step 22 .
18. Repair open or short to ground in ignition feed circuit to ignition coil. After repairs, go to step 37 .
19. Repair open or short to ground in ignition feed circuit to ignition control module. After repairs, go to step 37 .
20. Check for poor connections at ignition control module. If connections are faulty, go to step 30 . If connections are okay, go to step 35 .
21. Check for poor connections at ignition coil. If connections are faulty, go to step 30 . If connections are okay, go to step 31 .
22. Check for poor connections at VCM. If connections are faulty, go to step 30 . If connections are okay, go to step 36 .
23. Repair open in ignition control module ground circuit. After repairs, go to step 37 .
24. Repair open in ignition control circuit between VCM and ignition control module. After repairs, go to step 37 .
25. Repair short to ground in ignition control circuit between VCM and ignition control module. After repairs, go to step 37 .
26. Repair short to voltage in ignition control circuit between VCM and ignition control module. After repairs, go to step 37 .
27. Repair open in ignition coil driver circuit between ignition coil and ignition control module. After repairs, go to step 37 .
28. Repair short to ground in coil driver circuit between ignition coil and ignition control module. After repairs, go to step 37 .
29. Repair short to ground in tachometer input circuit between ignition coil and instrument cluster. After repairs, go to step 37 .
30. Repair faulty circuit as necessary. After repairs, go to step 37 .
31. Replace ignition coil. After repairs, go to step 37 .
32. Replace coil wire. After repairs, go to step 37 .
33. Replace distributor rotor. After repairs, go to step 37 .
34. Replace distributor cap. After repairs, go to step 37 .
35. Replace ignition control module. After repairs, go to step 37 .
36. Replace VCM. Perform VCM relearn procedures. After repairs, go to next step.
37. Operate system to verify repairs. If system operation is okay, testing is complete. If system operation is not okay, go to step 1 .

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Connect scan tool. Turn ignition on. Using scan tool, command fuel pump relay on and off. If fuel pump turns on and off, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If fuel pump does not turn on and off, go to next step.
3. Using scan tool, command fuel pump relay on and off. If fuel pump relay clicks, go to step 9 . If fuel pump relay does not click, go to next step.
4. Turn ignition off. Disconnect fuel pump relay located in underhood electrical center. Turn ignition on. Using test light connected to ground, probe fuel pump relay control circuit at relay cavity. Using scan tool, command fuel pump relay on and off. If test light turns on and off, go to next step. If test light does not turn on and off, go to step 6 .
5. Connect test light between fuel pump relay control circuit and fuel pump relay ground circuit at relay cavities. Using scan tool, command fuel pump relay on and off. If test light turns on and off, go to step 19 . If test light does not turn on and off, go to step 22 .
6. If test light remains illuminated with each command, go to next step. If test light does not illuminate at all, go to step 8 .
7. Disconnect VCM. Check for short to voltage in fuel pump relay control circuit. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to step 26 .
8. Disconnect VCM. Check for open or short to ground in fuel pump relay control circuit. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to step 20 .
9. Turn ignition on. If fuel pump runs continuously, go to next step. If fuel pump does not run continuously, go to step 11 .
10. Turn ignition off. Disconnect fuel pump relay located in underhood electrical center. Turn ignition on. If fuel pump runs continuously, go to step 21 . If fuel pump does not run continuously, go to step 25 .
11. Check ECM B fuse (20-amp) located in underhood fuse block. If fuse is open, go to next step. If fuse is okay, go to step 14 .
12. Check for short to ground in fuel pump power feed circuit between fuel pump and fuse. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
13. Reconnect all components. Install NEW ECM B fuse. Using scan tool, command fuel pump relay on. If fuse blows, go to step 24 . If fuse does not blow, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article.
14. Turn ignition off. Disconnect fuel pump relay located in underhood electrical center. Turn ignition on. Using test light connected to ground, probe fuel pump relay battery feed circuit at relay cavity. If test light illuminates, go to next step. If test light does not illuminate, go to step 23 .
15. Connect fused jumper wire between fuel pump relay battery feed circuit and fuel pump power feed circuit at relay cavities. If fuel pump runs, go to step 19 . If fuel pump does not run, go to next step.
16. Check for open or high resistance in fuel pump power feed circuit between fuel pump relay and fuel pump. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
17. Check for open or high resistance in fuel pump ground circuit. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
18. Check for poor connections at fuel pump. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 24 .
19. Check for poor connections at fuel pump relay. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 25 .
20. Check for poor VCM harness connections. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 26 .
21. Repair short to voltage in fuel pump power feed circuit. After repairs, go to step 27 .
22. Repair open in fuel pump relay ground circuit. After repairs, go to step 27 .
23. Repair open in fuel pump relay battery feed circuit. After repairs, go to step 27 .
24. Replace fuel pump. After repairs, go to step 27 .
25. Replace fuel pump relay. After repairs, go to step 27 .
26. Replace VCM. Perform VCM relearn procedures. After repairs, go to next step.
27. Operate system to verify repairs. If system operation is okay, testing is complete. If system operation is not okay, go to step 2 .

NO START-ENGINE CRANKS OKAY (4.8L, 5.3L & 6.0L)

Note. Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. If DTCs P0230, P0335, P0336, P0601, P0602, P0604, P1626, P1631 or any "U" codes are set, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If no DTCs are set, go to next step.
3. Using scan tool, check BCM for DTCs related to Vehicle Theft Deterrent (VTD) system. If any VTD DTCs are set, diagnose DTCs. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If no VTD DTCs are set, go to next step.
4. Using scan tool, monitor engine speed while cranking engine. If engine RPM is displayed, go to next step. If engine RPM is not displayed, go to step 6 .
5. Turn ignition on. Using test light connected to ground, probe both sides of the following fuses, located in underhood electrical center: INJR A (15-amp) INJR B (15-amp) ECM I (10-amp) If test light illuminates at both sides of all fuses, go to step 9 . If test light does not illuminate at both sides of all fuses, diagnose ignition relay. See «IGNITION RELAY DIAGNOSIS»(ref-3909-S09720614432000052300000) .
6. Disconnect CKP sensor harness connector. Measure voltage between ground and ignition feed circuit at CKP harness connector. If battery voltage is present, go to step 13 . If battery voltage is not present, go to next step.
7. Disconnect CMP sensor harness connector. Measure voltage between ground and ignition feed circuit at CMP harness connector. If battery voltage is present, go to step 14 . If battery voltage is not present, go to next step.
8. Check CKP sensor and CMP sensor ignition feed circuits for short to ground. Repair as necessary. After repairs, go to step 16 . If circuits are okay, go to step 15 .
9. Using scan tool, check engine coolant temperature. If displayed temperature is close to actual engine temperature, go to next step. If displayed temperature is not close to actual engine temperature, diagnose using diagnostic procedure for DTC P0118. See appropriate SELF-DIAGNOSTICS article.
10. Using scan tool, command fuel pump on. If fuel pump runs, go to next step. If fuel pump does not run, see «FUEL PUMP ELECTRICAL CIRCUIT»(ref-3909-S28857373132000052300000) .
11. Turn ignition off. Connect fuel pressure gauge. Turn ignition on. Observe fuel pressure while fuel pump is running. If fuel pressure is 55-62 psi (3.9-4.4 kg/cm 2 ), go to next step. If fuel pressure is not as specified, diagnose fuel system. See «BASIC FUEL SYSTEM CHECKS (GASOLINE)»(ref-3909-S32232778352000052300000) .
12. Perform the following checks: Check air duct between MAF sensor and throttle body for air leaks. Using scan tool, ensure throttle angle is at zero percent with throttle closed. If throttle angle is not as specified, diagnose using appropriate diagnostic procedure for TP sensor DTCs. See appropriate SELF-DIAGNOSTICS article. Replace MAF sensor if engine starts and continues to run with MAF sensor harness disconnected. Check for fouled spark plugs. If fouled, determine cause and repair as necessary. Check for possible engine mechanical failure causing a no start condition. Compare MAP sensor and barometric pressure (BARO) sensor values to that of another vehicle. Sensor values should be similar. Repair as necessary. After repairs, go to step 16 . If no problem is found, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article.
13. Replace CKP sensor. After repairs, go to step 16 .
14. Replace CMP sensor. After repairs, go to step 16 .
15. Replace PCM. Perform PCM relearn procedures. After repairs, go to next step.
16. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, go to step 2 .
17. Allow engine to reach normal operating temperature. Using scan tool, check for DTCs. If any DTCs are set, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If no DTCs are set, go to next step.
18. Using scan tool, select CAPTURE INFO and REVIEW INFO function. If any DTCs are set that have not been diagnosed, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If no DTCs are set, system is okay.

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Connect scan tool. Turn ignition on. Using scan tool, command fuel pump relay on and off. If fuel pump turns on and off, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If fuel pump does not turn on and off, go to next step.
3. Using scan tool, command fuel pump relay on and off. If fuel pump relay clicks, go to step 9 . If fuel pump relay does not click, go to next step.
4. Turn ignition off. Disconnect fuel pump relay located in underhood junction block. Turn ignition on. Using test light connected to ground, probe fuel pump relay control circuit at relay cavity. Using scan tool, command fuel pump relay on and off. If test light turns on and off, go to next step. If test light does not turn on and off, go to step 6 .
5. Connect test light between fuel pump relay control circuit and fuel pump relay ground circuit at relay cavities. Using scan tool, command fuel pump relay on and off. If test light turns on and off, go to step 19 . If test light does not turn on and off, go to step 22 .
6. If test light remains illuminated with each command, go to next step. If test light does not illuminate at all, go to step 8 .
7. Disconnect PCM. Check for short to voltage in fuel pump relay control circuit. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to step 26 .
8. Disconnect PCM. Check for open or short to ground in fuel pump relay control circuit. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to step 20 .
9. Turn ignition on. If fuel pump runs continuously, go to next step. If fuel pump does not run continuously, go to step 11 .
10. Turn ignition off. Disconnect fuel pump relay located in underhood junction block. Turn ignition on. If fuel pump runs continuously, go to step 21 . If fuel pump does not run continuously, go to step 25 .
11. Check ECM B fuse (20-amp) located in underhood junction block. If fuse is open, go to next step. If fuse is okay, go to step 14 .
12. Check for short to ground in fuel pump power feed circuit between fuel pump and fuse. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
13. Reconnect all components. Install NEW ECM B fuse. Using scan tool, command fuel pump relay on. If fuse blows, go to step 24 . If fuse does not blow, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article.
14. Turn ignition off. Disconnect fuel pump relay located in underhood junction block. Turn ignition on. Using test light connected to ground, probe fuel pump relay battery feed circuit at relay cavity. If test light illuminates, go to next step. If test light does not illuminate, go to step 23 .
15. Connect fused jumper wire between fuel pump relay battery feed circuit and fuel pump power feed circuit at relay cavities. If fuel pump runs, go to step 19 . If fuel pump does not run, go to next step.
16. Check for open or high resistance in fuel pump power feed circuit between fuel pump relay and fuel pump. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
17. Check for open or high resistance in fuel pump ground circuit. Repair as necessary. After repairs, go to step 27 . If circuit is okay, go to next step.
18. Check for poor connections at fuel pump. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 24 .
19. Check for poor connections at fuel pump relay. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 25 .
20. Check for poor PCM harness connections. Repair as necessary. After repairs, go to step 27 . If connections are okay, go to step 26 .
21. Repair short to voltage in fuel pump power feed circuit. After repairs, go to step 27 .
22. Repair open in fuel pump relay ground circuit. After repairs, go to step 27 .
23. Repair open in fuel pump relay battery feed circuit. After repairs, go to step 27 .
24. Replace fuel pump. After repairs, go to step 27 .
25. Replace fuel pump relay. After repairs, go to step 27 .
26. Replace PCM. Perform PCM relearn procedures. After repairs, go to next step.
27. Operate system to verify repairs. If system operation is okay, testing is complete. If system operation is not okay, go to step 2 .

NO START-ENGINE CRANKS OKAY (6.5L DIESEL)

Note. Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

Basic System Check

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Check battery condition. If batteries are okay, go to next step. If condition of batteries is not okay, go to step 23 .
3. Check fuel level in tank. If fuel level is okay, go to next step. If fuel level is not okay, go to step 23 .
4. Check quality of fuel. If fuel quality is okay, go to next step. If fuel quality is not okay, go to step 23 .
5. Check glow plug operation. If glow plug operation is okay, go to next step. If glow plug operation is not okay, go to step 23 .
6. Check for proper engine cranking speed. If engine cranking speed is okay, go to next step. If engine cranking speed is not okay, go to step 23 .
7. Check for restriction in fuel return system. If restriction is not present, go to next step. If return line is restricted, go to step 23 .
8. Check injection pump ground wire located on top of injection pump. If ground wire is okay, go to next step. If ground wire is not okay, go to step 23 .
9. Install scan tool. Using scan tool, check for any data. If data is displayed, go to next step. If data is not displayed, see DLC DIAGNOSIS OR NO SCAN TOOL DATA in appropriate SELF-DIAGNOSTICS article.
10. Using scan tool, monitor Vehicle Theft Deterrent (VTD) FUEL DISABLED parameter on ENGINE DATA 1 list. Crank engine. If scan tool displays ACTIVE while engine is cranked, diagnose VTD system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If scan tool does not display ACTIVE, go to next step.
11. Loosen injector line at injector. Crank engine and check for fuel. Repeat procedure for all injectors. If fuel flows from each fuel line, go to step 17 . If fuel does not flow from each fuel line, go to next step.
12. Disconnect optical/fuel temperature sensor. Attempt to start engine. If engine starts, go to step 16 . If engine does not start, go to next step.
13. Reconnect optical/fuel temperature sensor. Disconnect fuel solenoid driver at fuel injection pump. Measure voltage between ground and fuel injector control circuit at harness connector while cranking engine. If voltage is 1.2 volts or greater, go to next step. If voltage is less than 1.2 volts, go to step 18 .
14. With fuel solenoid driver still disconnected, probe solenoid ground circuit at harness connector with test light connected to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 19 .
15. Turn ignition on. Ensure fuel solenoid driver is still disconnected. Using test light connected to ground, probe ignition feed circuit at fuel solenoid harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 21 .
16. Replace fuel injection pump. After repairs, go to step 25 .
17. Injection system is okay. Check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article.
18. Check for open or short to ground in fuel injector control circuit between fuel solenoid driver and PCM. Repair as necessary. After repairs, go to step 22 . If circuit is okay, go to step 20 .
19. Check closure signal ground circuit for open between fuel solenoid driver and PCM. Repair as necessary. After repairs, go to step 22 . If circuit is okay, go to next step.
20. Check for poor connections at fuel solenoid driver and PCM harness connectors. Repair as necessary. After repairs, go to step 22 . If connections are okay, go to step 24 .
21. Repair open in ignition feed circuit. After repairs, go to step 25 .
22. Repair circuit as necessary. After repairs, go to step 25 .
23. Repair as necessary. After repairs, go to step 25 .
24. Replace PCM. Perform PCM relearn procedures. After repairs, go to next step.
25. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and stalls, go to step 2 .
26. Allow engine to reach normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any DTCs are set, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If no DTCs are set, go to next step.
27. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any other DTCs are set that have not been diagnosed, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If DTCs are not set, system is okay.

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Turn ignition off for 10 seconds. Turn ignition on. Fuel lift pump should run during glow plug cycle. If fuel lift pump runs, see «BASIC SYSTEM CHECK»(ref-3909-S38070470652000052300000) . If fuel lift pump does not run, go to next step.
3. Remove fuel pump relay located in underhood electrical center. Using fused jumper wire, jumper fuel pump relay battery feed circuit and fuel lift pump power feed circuit together at fuel pump relay cavities. If fuel lift pump runs, go to next step. If fuel lift pump does not run, leave jumper wire connected and go to step 8 .
4. Turn ignition on. Using test light connected to ground, probe fuel pump relay battery feed circuit at relay cavity. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
5. Connect test light between fuel pump relay battery feed circuit and fuel pump relay ground circuit at relay cavities. If test light illuminates, go to next step. If test light does not illuminate, go to step 11 .
6. Using test light connected to ground, probe fuel pump relay control circuit at relay cavity. Turn ignition off for 20 seconds. Turn ignition on. If test light illuminates during glow plug cycle, and then turns off, go to next step. If test light does not illuminate, and then turn off, go to step 12 .
7. Check for faulty connections at fuel pump relay. Repair as necessary. After repairs, go to step 18 . If connections are okay, go to step 13 .
8. Disconnect fuel lift pump harness connector at fuel lift pump. Using test light connected to ground, probe fuel lift pump power feed circuit at harness connector (vehicle side). If test light illuminates, go to next step. If test light does not illuminate, go to step 15 .
9. Using test light connected to battery voltage, probe fuel lift pump ground circuit at fuel lift pump harness connector (vehicle side). If test light illuminates, go to step 14 . If test light does not illuminate, go to step 16 .
10. Repair open in fuel pump relay battery feed circuit. After repairs, go to step 18 .
11. Repair open in fuel pump relay ground circuit. After repairs, go to step 18 .
12. Check for open or short to ground in fuel pump relay control circuit between PCM and fuel pump relay. Repair as necessary. After repairs, go to step 18 . If circuit is okay, go to step 17 .
13. Replace fuel pump relay. After repairs, go to step 18 .
14. Replace fuel lift pump. After repairs, go to step 18 .
15. Repair open or high resistance in fuel lift pump power feed circuit between fuel pump relay and fuel lift pump. After repairs, go to step 18 .
16. Repair open in fuel lift pump ground circuit. After repairs, go to step 18 .
17. Replace PCM. Perform PCM replacement procedures. After repairs, go to next step.
18. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and stalls, go to step 2 .
19. Allow engine to reach normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any DTCs are set, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If DTCs are not set, go to next step.
20. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any other DTCs are set that have not been diagnosed, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If DTCs are not set, system is okay.

FUEL SYSTEM PRESSURE RELIEF

Note. For fuel pump circuit testing, see appropriate diagnostic procedure under NO START DIAGNOSIS .

Fuel system is under pressure. Pressure must be relieved prior to servicing fuel system. Fuel pressure may be relieved by using the following method

1. Disconnect negative battery cable. Loosen fuel filler cap. Install Fuel Pressure Gauge (J-34730-1A) to fuel pressure connection. Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Place gauge bleed hose in container. Open bleed valve to relieve fuel pressure.

2.2L

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Turn ignition off. Turn A/C system off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Install Fuel Pressure Gauge (J-29658-D). This kit modifies fuel pressure gauge so it may be installed in fuel delivery line with quick-connect fittings. Place fuel pressure gauge bleed hose into container. Connect negative battery cable. Turn ignition on. Bleed air from fuel pressure gauge. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should run for about 2 seconds. Cycle ignition switch to obtain highest fuel pressure possible. Observe fuel pressure with fuel pump running. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, go to step 12 .
3. Fuel pressure may vary slightly when fuel pump stops. After fuel pump stops, fuel pressure should stabilize and remain constant. Note fuel pressure when fuel pump stops running. If fuel pressure decreases more than 5 psi (0.3 kg/cm 2 ) in 10 minutes, go to step 10 . If fuel pressure does not decrease more than 5 psi (0.3 kg/cm 2 ) in 10 minutes, go to next step.
4. Relieve fuel pressure until pressure is 10 psi (0.7 kg/cm 2 ). If fuel pressure decreases more than 2 psi (0.1 kg/cm 2 ) in 10 minutes, go to step 21 . If fuel pressure does not decrease more than 2 psi (0.1 kg/cm 2 ) in 10 minutes, go to next step.
5. If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering, go to next step. If fuel pressure is not suspected of decreasing during acceleration, cruise or hard corning, go to step 8 .
6. Inspect in-line fuel filter and fuel feed pipe for restriction. If restriction is found, go to step 24 . If restriction is not found, go to next step.
7. Remove fuel sending unit assembly. Inspect fuel pump strainer for restriction, proper positioning and installation on fuel sending unit assembly. Check fuel pump flex pipe for leaks and ensure fuel pump is correct for vehicle application. If problem is found, go to step 24 . If no problem is found, go to step 20 .
8. Start engine. Observe fuel pressure. If fuel pressure is 31-44 psi (2.2-3.1 kg/cm 2 ), system is okay at this time. Check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If fuel pressure is not as specified, go to next step.
9. Disconnect vacuum hose from fuel pressure regulator. With engine idling, apply vacuum (12-14 in. Hg) to fuel pressure regulator. If fuel pressure is 31-44 psi (2.2-3.1 kg/cm 2 ) and remains constant, go to step 19 . If fuel pressure is not as specified, go to step 20 .
10. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Place bleed hose into container. Turn ignition on. Bleed air from fuel pressure gauge. Using scan tool, pressurize fuel system. Wait for fuel pressure to build. Using scan tool, obtain highest fuel pressure possible. Gradually pinch off fuel feed hose. If fuel pressure remains constant, go to step 21 . If fuel pressure does not remain constant, go to next step.
11. Gradually unpinch fuel feed hose. Using scan tool, pressurize fuel system. Wait for fuel pressure to build. Gradually pinch off fuel return hose. If fuel pressure remains constant, go to step 20 . If fuel pressure does not remain constant, go to step 22 .
12. If fuel pressure is greater than 47 psi (3.3 kg/cm 2 ), go to next step. If fuel pressure is not greater than 47 psi (3.3 kg/cm 2 ), go to step 15 .
13. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Disconnect fuel return pipe from fuel rail. Attach flexible fuel hose to fuel rail return outlet passage. Place other end of flexible hose into container. Turn ignition off for about 10 seconds. Turn ignition on. Observe fuel pressure gauge with fuel pump running. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is within specification, go to step 23 . If fuel pressure is not within specification, go to next step.
14. Inspect fuel rail outlet passage for restriction. If restriction is found, go to step 24 . If no restriction is found, go to step 20 .
15. If fuel pressure is greater than zero psi, go to next step. If fuel pressure is zero psi, go to step 17 .
16. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Place bleed hose into container. Turn ignition on. Bleed air from fuel pressure gauge. Using scan tool, pressurize fuel system. DO NOT allow fuel pressure to exceed 60 psi (4.2 kg/cm 2 ). Excess pressure may damage fuel pressure regulator. Wait for fuel pressure to build. Using scan tool, obtain highest fuel pressure possible. Gradually pinch off fuel return hose. If fuel pressure increases to greater than 47 psi (3.3 kg/cm 2 ), go to step 20 . If fuel pressure does not increase to greater 47 psi (3.3 kg/cm 2 ), go to step 7 .
17. Check fuel pump electrical circuit. See appropriate diagnostic procedure under «NO START DIAGNOSIS»(ref-3909-S08784751642000052300000) . If problem is found in electrical circuit, go to step 24 . If electrical circuit is okay, go to next step.
18. Remove fuel sending unit assembly. Inspect in-line fuel filter, fuel feed pipe and fuel pump strainer for restrictions. Check fuel pump flex pipe for leaks. If problem is found, go to step 24 . If no problem is found, go to step 21 .
19. Locate and repair loss of vacuum to fuel pressure regulator.
20. Replace fuel pressure regulator.
21. Replace fuel sending unit assembly.
22. Locate and replace leaking fuel injector(s).
23. Locate and repair restriction in fuel return pipe.
24. Repair problem as necessary.

3.4L

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Turn ignition off. Turn A/C system off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure fitting on fuel rail. Place fuel pressure gauge bleed hose into container. Connect negative battery cable. Turn ignition on. Bleed air from fuel pressure gauge. Using scan tool, command fuel pump on. Observe fuel pressure with fuel pump running. Fuel pressure should be 52-59 psi (3.7-4.1 kg/cm 2 ). If fuel pressure is within specification, go to step 6 . If fuel pressure is not within specification, go to next step.
3. If indicated fuel pressure is greater than 59 psi (4.1 kg/cm 2 ), go to step 14 . If indicated fuel pressure is not greater than 59 psi (4.1 kg/cm 2 ), go to next step.
4. Check fuel system for leaks. Repair as necessary. After repairs, go to step 21 . If no leaks are present, go to next step.
5. If indicated fuel pressure is greater than zero psi, go to step 7 . If indicated fuel pressure is not greater than zero psi, go to step 16 .
6. Monitor fuel pressure. If fuel pressure decreases more than 5 psi (.4 kg/cm 2 ) in 10 minutes, go to next step. If pressure does not decrease more than 5 psi (.4 kg/cm 2 ) in 10 minutes, go to step 9 .
7. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Connect Fuel Pipe Shutoff Adapters (J-37287) between fuel feed pipe and fuel return pipe at fuel rail. Open fuel feed and close fuel return valves. Turn ignition on. Bleed air from fuel system. Using scan tool, command fuel pump on and wait for pressure to build. If fuel pressure is constant at 52-59 psi (3.7-4.1 kg/cm 2 ), go to step 19 . If fuel pressure is not as specified, go to next step.
8. Using scan tool, command fuel pump on. With fuel pump running, close fuel feed valve. If fuel pressure is constant, go to step 17 . If fuel pressure is not constant, diagnose fuel injectors. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article.
9. If fuel pressure is suspected of dropping off during acceleration, cruise or hard cornering, go to next step. If fuel pressure is not suspected of dropping off during acceleration, cruise or hard cornering, go to step 12 .
10. Check in-line fuel filter and fuel feed pipe for restriction. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
11. Remove fuel sending unit assembly. Check pump strainer for restriction or incorrect installation. Check for leaking fuel pump flex pipe. Ensure fuel pump is correct for vehicle application. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to step 17 .
12. Start engine and allow it to reach normal operating temperature. Observe fuel pressure gauge. If fuel pressure decreases 3-10 psi (.2-.7 kg/cm 2 ), check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If fuel pressure does not decrease 3-10 psi (.2-.7 kg/cm 2 ), go to next step.
13. With engine idling, disconnect vacuum hose from fuel pressure regulator. Apply vacuum (12 in. Hg) to fuel pressure regulator. If fuel pressure decreases 3-10 psi (.2-.7 kg/cm 2 ), go to step 18 . If fuel pressure does not decrease 3-10 psi (.2-.7 kg/cm 2 ), go to step 19 .
14. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Disconnect fuel return pipe. Connect flexible fuel hose to fuel rail return outlet. Place open end of hose into container. Using scan tool, command fuel pump on. Observe fuel pressure gauge. If fuel pressure is 52-59 psi (3.7-4.1 kg/cm 2 ), go to step 20 . If fuel pressure is not as specified, go to next step.
15. Check fuel rail outlet for restriction. Repair as necessary. After repairs, go to step 21 . If no restriction is found, go to step 19 .
16. Check for clogged in-line fuel filter or fuel pump strainer, restricted fuel feed pipe or leaks in fuel pump flex pipe. Repair as necessary. After repairs, go to step 21 . If no problem is found, diagnose fuel pump electrical circuit. See appropriate diagnostic procedure under «NO START DIAGNOSIS»(ref-3909-S08784751642000052300000) .
17. Replace fuel sending unit assembly. After repairs, go to step 21 .
18. Locate and repair loss of vacuum to fuel pressure regulator. After repairs, go to step 21 .
19. Replace fuel pressure regulator. After repairs, go to step 21 .
20. Repair restriction in fuel return pipe. After repairs, go to next step.
21. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Reconnect all fuel system components, leaving fuel pressure gauge installed. Turn ignition on. Using scan tool, command fuel pump on. Monitor fuel pressure with fuel pump running. If fuel pressure is constant at 52-59 psi (3.7-4.1 kg/cm 2 ), system is okay. If fuel pressure is not as specified, go to step 2 .

4.3L

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Turn ignition off. Turn A/C system off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure test port. Using scan tool, command fuel pump on. Bleed air from fuel pressure gauge into container. Using scan tool, command fuel pump on. Monitor fuel pressure with fuel pump running. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 11 .
3. If fuel pressure decreases more than 5 psi (.4 kg/cm 2 ) within 10 minutes after fuel pump turns off, go to step 8 . If fuel pressure does not decrease more than 5 psi (.4 kg/cm 2 ) within 10 minutes after fuel pump turns off, go to next step.
4. Relieve fuel pressure until gauge reads 10 psi (.7 kg/cm 2 ). Monitor fuel pressure. If fuel pressure decreases more than 2 psi (.1 kg/cm 2 ) within 10 minutes, go to step 20 . If fuel pressure does not decrease more than 2 psi (.1 kg/cm 2 ) within 10 minutes, go to next step.
5. If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering, go to step 7 . If fuel pressure is not suspected of decreasing during acceleration, cruise or hard corning, go to next step.
6. Start engine and allow it to reach normal operating temperature. Open throttle quickly. Observe fuel pressure. Fuel pressure should increase to about 66 psi (4.6 kg/cm 2 ). If fuel pressure increases quickly, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If fuel pressure does not increase quickly, go to next step.
7. Check for restriction in fuel filter or fuel feed pipe. Check fuel pump electrical circuit for high resistance. If problem is found, go to step 24 . If no problem is found, go to step 16 .
8. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Remove EVAP canister. Disconnect fuel feed pipe from either side of fuel filter. Drain remaining fuel from fuel pipe into container. Connect Fuel Pipe Shutoff Adapter (J-42964-1) onto fuel feed pipe. Open valve on shutoff adapter. Install fuel pressure gauge onto shutoff adapter pressure test connection farthest from fuel tank. Reconnect negative battery cable. Turn ignition on. Using scan tool, command fuel pump on. Check for leaks at fittings. Place bleed hose of fuel pressure gauge into container. Bleed air from fuel pressure gauge. Using scan tool, command fuel pump on and wait for pressure to build. Close valve on shutoff adapter connected to fuel feed pipe. Monitor fuel pressure. If fuel pressure remains constant, go to step 20 . If fuel pressure does not remain constant, go to next step.
9. Check fuel feed pipe for leak between shutoff adapter and engine fuel pipe. If a leak is found, go to step 24 . If no leaks are found, go to next step.
10. Open valve in shutoff adapter connected to fuel feed pipe. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Disconnect fuel return pipe located near EVAP canister. Drain remaining fuel from fuel pipe into container. Connect Fuel Pipe Shutoff Adapter (J-42964-2) onto fuel return pipe. Open valve in shutoff adapter connected to fuel return pipe. Reconnect negative battery cable. Turn ignition on. Using scan tool, command fuel pump on and wait for pressure to build. Close valve in shutoff adapter connected to fuel return pipe. Monitor fuel pressure. If fuel pressure remains constant, go to step 21 . If fuel pressure does not remain constant, go to step 22 .
11. If fuel pressure is greater than 66 psi (4.6 kg/cm 2 ), go to next step. If fuel pressure is not greater than 66 psi (4.6 kg/cm 2 ), go to step 14 .
12. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Remove EVAP canister. Disconnect fuel feed pipe from either side of fuel filter. Disconnect fuel return pipe located near EVAP canister. Drain remaining fuel from fuel pipe into container. Connect Fuel Pipe Shutoff Adapter (J-42964-1) onto fuel feed pipe. Open valve on shutoff adapter. Install fuel pressure gauge onto shutoff adapter pressure test connection. Connect flexible fuel hose to chassis fuel return pipe. Place open end of hose into container. Reconnect negative battery cable. Turn ignition on. Using scan tool, command fuel pump on. Monitor fuel pressure with fuel pump running. If fuel pressure is 60-66 psi (4.2-4.6 kg/cm 2 ), go to step 23 . If fuel pressure is not as specified, go to next step.
13. Check engine compartment and chassis fuel pipes for restriction. If a restriction is found, go to step 24 . If no restriction is found, go to step 21 .
14. If fuel pressure is greater than zero psi, go to next step. If fuel pressure is not greater than zero psi, go to step 17 .
15. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Remove EVAP canister. Disconnect fuel feed pipe from either side of fuel filter. Disconnect fuel return pipe located near EVAP canister. Drain remaining fuel from fuel pipe into container. Connect Fuel Pipe Shutoff Adapters (J-42964-1 and J-42964-2) onto fuel feed and return pipes. Open valves on shutoff adapters. Install fuel pressure gauge onto either shutoff adapter pressure test connection. Reconnect negative battery cable. Turn ignition on. Using scan tool, command fuel pump on. Check for leaks at adapter fittings. Place fuel pressure gauge bleed hose into container. Bleed air from fuel pressure gauge. Using scan tool, command fuel pump on. DO NOT allow fuel pressure to exceed 75 psi (5.3 kg/cm 2 ). Slowly close valve on adapter connected to fuel return pipe. Monitor fuel pressure with fuel pump running. If fuel pressure increases to more than 66 psi (4.6 kg/cm 2 ), go to step 21 . If fuel pressure does not increase to more than 66 psi (4.6 kg/cm 2 ), go to next step.
16. Check for high resistance in fuel system electrical circuits. Check for leaks or restrictions in fuel system. Ensure fuel pump is correct for vehicle application. If a problem is found, go to step 24 . If no problem is found, go to step 20 .
17. Turn ignition on. Using scan tool, command fuel pump on. If fuel pump runs, go to next step. If fuel pump does not run, diagnose fuel pump electrical circuit. See appropriate diagnostic procedure under «NO START DIAGNOSIS»(ref-3909-S08784751642000052300000) .
18. Check for appropriate amount of fuel in tank. Check for restrictions in fuel filter, fuel feed pipe and fuel pump strainer. Check for leaks in fuel pump flex pipe. If a problem is found, go to step 24 . If no problem is found, go to next step.
19. Check for fuel leaks in fuel feed pipe between shutoff adapter and fuel sending unit. If a leak is found, go to step 24 . If no leaks are found, go to next step.
20. Replace fuel pump.
21. Replace fuel pressure regulator.
22. Replace any leaking or grounded fuel injectors.
23. Repair restriction in fuel return pipe.
24. Repair problem as necessary.

5.0L, 5.7L & 7.4L

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure test port. Using scan tool, command fuel pump on. Bleed air from fuel pressure gauge into container. Using scan tool, command fuel pump on. Monitor fuel pressure with fuel pump running. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ) on CSI system and 56-62 psi (4.0-4.4 kg/cm 2 ) on SFI system. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 8 .
3. Using scan tool, command fuel pump on. Fuel pump should run for 2 seconds. Observe fuel pressure after fuel pump stops running. After fuel pump stops, fuel pressure should stabilize and remain constant at 55-60 psi (3.9-4.2 kg/cm 2 ) on CSI system and 48-52 psi (3.4-3.7 kg/cm 2 ) on SFI system. If pressure is within specification and holds, go to step 5 . If pressure is not as specified, go to next step.
4. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Disconnect fuel filter. Drain any remaining fuel from fuel pipes into container. Install appropriate fuel line shutoff valve in place of fuel filter. Open shutoff valve. Using scan tool, command fuel pump on. Check for leaks at shutoff valve. Start engine and idle for 30 seconds. Turn ignition off for 10 seconds. Turn ignition on. Using scan tool, command fuel pump on. Wait for fuel pressure to build. Close shutoff valve. Fuel pressure should remain constant at 55-60 psi (3.9-4.2 kg/cm 2 ) on CSI system and 48-52 psi (3.4-3.7 kg/cm 2 ) on SFI system. If pressure is as specified and holds, go to step 12 . If pressure is not as specified, go to step 6 .
5. If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering, go to step 27 . If fuel pressure is not suspected of decreasing during acceleration, cruise or hard corning, go to step 26 .
6. Check fuel feed line between shutoff valve and fuel pipes. If fuel feed line is faulty, go to step 25 . If fuel feed line is okay, go to next step.
7. Open shutoff valve. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install appropriate fuel line shutoff valve in place of fuel return pipe union. Open shutoff valve. Using scan tool, command fuel pump on. Check for leaks at fuel shutoff valve fittings. Start engine and idle for 30 seconds. Turn ignition off for 10 seconds. Turn ignition on. Using scan tool, command fuel pump on. Wait for fuel pressure to build. Close shutoff valve installed on fuel return pipe. If fuel pressure remains constant, go to step 22 . If fuel pressure does not remain constant, go to step 29 .
8. Turn ignition on. Using scan tool, command fuel pump on. Fuel pump should run for 2 seconds, and then turn off. Observe fuel pressure after fuel pump stops running. If fuel pressure is present, go to step 13 . If fuel pressure is not present, go to next step.
9. Turn ignition on. Using scan tool, command fuel pump on. Listen for fuel pump operation. If fuel pump operates, go to next step. If fuel pump does not operate, diagnose fuel pump electrical circuit. See appropriate diagnostic procedure under «NO START DIAGNOSIS»(ref-3909-S08784751642000052300000) .
10. Check for restricted fuel filter, fuel pump strainer or fuel line. If problem is found, go to next step. If no problem is found, go to step 12 .
11. Repair or replace as necessary. After repairs, go to step 30 .
12. Replace fuel sending unit assembly. After repairs, go to step 30 .
13. Turn ignition on. Using scan tool, command fuel pump on. Fuel pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is greater than 66 psi (4.6 kg/cm 2 ) on CSI system or greater than 62 psi (4.4 kg/cm 2 ) on SFI system, go to next step. If fuel pressure is not as specified, go to step 15 .
14. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Disconnect engine compartment fuel return line. Attach flexible hose to fuel return line. Place open end of hose in container. Using scan tool, command fuel pump on and observe fuel pressure within 2 seconds. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ) on CSI system and 56-62 psi (4.0-4.4 kg/cm 2 ) on SFI system. If fuel pressure is as specified, go to step 16 . If fuel pressure is not as specified, go to step 17 .
15. Turn ignition on. Using scan tool, command fuel pump on. Fuel pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is less than 60 psi (4.2 kg/cm 2 ) on CSI system or less than 56 psi (4.0 kg/cm 2 ) on SFI system, go to step 19 . If fuel pressure is not as specified, go to step 30 .
16. Locate and repair restriction in fuel return line. After repairs, go to step 30 . If fuel return line is not restricted, go to next step.
17. Check for restriction in engine fuel return outlet pipe at point where fuel line was disconnected. If fuel return pipe is restricted, go to next step. If fuel return pipe is not restricted, go to step 22 .
18. Replace engine fuel pipes. After repairs, go to step 30 .
19. Inspect in-line fuel filter and fuel line for restriction. If restriction is found, go to next step. If restriction is not found, go to step 21 .
20. Repair or replace in-line fuel filter and fuel line as necessary. After repairs, go to step 30 .
21. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install appropriate fuel line shutoff valve in place of fuel return pipe union. Open shutoff valve. Using scan tool, command fuel pump on. Bleed air out of fuel pressure gauge into container. DO NOT allow fuel pressure to exceed 75 psi (4.5 kg/cm 2 ). Excess pressure may damage fuel pressure regulator. Slowly close shutoff valve installed on fuel return pipe. Fuel pressure should increase to greater than 66 psi (4.6 kg/cm 2 ) on CSI system or 62 psi (4.4 kg/cm 2 ) on SFI system. If fuel pressure increases as specified, go to next step. If fuel pressure does not increase as specified, go to step 23 .
22. Replace fuel pressure regulator. After repairs, go to step 30 .
23. Check for the following conditions: Low fuel pump voltage due to high resistance connections. High fuel pump voltage due to internal pump binding. Poor fuel pump ground. Partially restricted fuel pump strainer. Incorrect or faulty fuel pump. If any of the listed conditions are present, go to next step. If none of the listed conditions are present, go to step 12 .
24. Repair or replace as necessary. After repairs, go to step 30 .
25. Replace fuel feed line. After repairs, go to step 30 .
26. Start engine and allow it to reach normal operating temperature. Open throttle quickly. Observe fuel pressure. Fuel pressure should increase to about 66 psi (4.6 kg/cm 2 ) on CSI system or about 62 psi (4.4 kg/cm 2 ) on SFI system. If fuel pressure increases quickly, check for intermittent problem. See appropriate TROUBLE SHOOTING - NO CODES article. If fuel pressure does not increase quickly, go to next step.
27. Check for the following conditions: In-line fuel filter for restriction. Fuel feed pipe for restriction. Mispositioned or damaged fuel pump strainer. Fuel pump flex pipe for leaks. Vehicle is equipped with correct fuel pump. Fuel pump electrical wiring for high resistance. If any of the listed conditions are present, go to next step. If none of the listed conditions are present, go to step 12 .
28. Repair or replace as necessary. After repairs, go to step 30 .
29. Locate and replace any leaking injector(s). After repairs, go to next step. If no injectors leak, check fuel injector performance. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article.
30. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional DTCs are set, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If DTCs are not set, system is okay.

4.8L, 5.3L & 6.0L

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Turn ignition off. Turn A/C system off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Install Fuel Pressure Gauge (J-34730-1A). Place fuel pressure gauge bleed hose into container. Turn ignition on. Bleed air from fuel pressure gauge. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should run for about 2 seconds. Cycle ignition to obtain highest fuel pressure possible. Observe fuel pressure with fuel pump running. Fuel pressure should be 55-62 psi (3.9-4.4 kg/cm 2 ). If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, go to step 12 .
3. Fuel pressure may vary slightly when fuel pump stops. After fuel pump stops, fuel pressure should stabilize and remain constant. Note fuel pressure when fuel pump stops running. If fuel pressure decreases more than 5 psi (0.3 kg/cm 2 ) in 10 minutes, go to step 10 . If fuel pressure does not decrease more than 5 psi (0.3 kg/cm 2 ) in 10 minutes, go to next step.
4. Relieve fuel pressure until pressure is 10 psi (0.7 kg/cm 2 ). If fuel pressure decreases more than 2 psi (0.1 kg/cm 2 ) in 10 minutes, go to step 19 . If fuel pressure does not decrease more than 2 psi (0.1 kg/cm 2 ) in 10 minutes, go to next step.
5. If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering, go to next step. If fuel pressure is not suspected of decreasing during acceleration, cruise or hard corning, go to step 8 .
6. Inspect in-line fuel filter and fuel feed pipe for restriction. If restriction is found, go to step 24 . If no restriction is found, go to next step.
7. Remove fuel sending unit assembly. Inspect fuel pump strainer for restriction, proper positioning and installation on fuel sending unit assembly. Check fuel pump flex pipe for leaks and ensure fuel pump is correct for vehicle application. If a problem is found, go to step 24 . If no problem is found, go to step 19 .
8. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should run for about 2 seconds. Cycle ignition to obtain highest fuel pressure possible. Note fuel pressure. Start engine and allow it to reach normal operating temperature. If fuel pressure is less than previously noted pressure by 3-10 psi (0.2-0.7 kg/cm 2 ), see appropriate TROUBLE SHOOTING - NO CODES article. If fuel pressure is not less than previously noted pressure by 3-10 psi (0.2-0.7 kg/cm 2 ), go to next step.
9. Disconnect vacuum hose from fuel pressure regulator. With engine idling, apply vacuum (12-14 in. Hg) to fuel pressure regulator. If fuel pressure decreases by 3-10 psi (0.2-0.7 kg/cm 2 ), go to step 20 . If fuel pressure does not decrease by 3-10 psi (0.2-0.7 kg/cm 2 ), go to step 21 .
10. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Install appropriate fuel line shutoff valves in-line at fuel feed and fuel return lines. Open both shutoff valves. Using scan tool, pressurize fuel system. Wait for fuel pressure to build. Close shutoff valve at fuel feed line. If fuel pressure remains constant, go to step 19 . If fuel pressure does not remain constant, go to next step.
11. Open shutoff valve at fuel feed line. Using scan tool, pressurize fuel system. Wait for fuel pressure to build. Close shutoff valve at fuel return line. If fuel pressure remains constant, go to step 21 . If fuel pressure does not remain constant, go to step 22 .
12. If fuel pressure is greater than 62 psi (4.4 kg/cm 2 ), go to next step. If fuel pressure is not greater than 62 psi (4.4 kg/cm 2 ), go to step 15 .
13. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Disconnect fuel return pipe from fuel rail. Attach flexible fuel hose to fuel rail return outlet passage. Place other end of flexible hose into container. Turn ignition off for about 10 seconds. Turn ignition on. Observe fuel pressure gauge with fuel pump running. Fuel pressure should be 55-62 psi (3.9-4.4 kg/cm 2 ). If fuel pressure is within specification, go to step 23 . If fuel pressure is not within specification, go to next step.
14. Inspect fuel rail outlet passage for restriction. If restriction is found, go to step 24 . If no restriction is found, go to step 21 .
15. If fuel pressure is greater than zero psi, go to next step. If fuel pressure is zero psi, go to step 17 .
16. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(ref-3909-S35198353242000052300000) . Install appropriate fuel line shutoff valve in-line at fuel return line. Open shutoff valve. Using scan tool, pressurize fuel system. DO NOT allow fuel pressure to exceed 75 psi (5.3 kg/cm 2 ). Excess pressure may damage fuel pressure regulator. Wait for fuel pressure to build. Gradually close shutoff valve at return line. If fuel pressure increases to greater than 62 psi (4.4 kg/cm 2 ), go to step 21 . If fuel pressure does not increase to greater 62 psi (4.4 kg/cm 2 ), go to step 7 .
17. Using scan tool, command fuel pump on. If fuel pump runs, go to next step. If fuel pump does not run, check fuel pump electrical circuit. See appropriate diagnostic procedure under «NO START DIAGNOSIS»(ref-3909-S08784751642000052300000) .
18. Remove fuel sending unit assembly. Inspect in-line fuel filter, fuel feed pipe and fuel pump strainer for restrictions. Check fuel pump flex pipe for leaks. If a problem is found, go to step 24 . If no problem is found, go to next step.
19. Replace fuel sending unit assembly.
20. Locate and repair loss of vacuum to fuel pressure regulator.
21. Replace fuel pressure regulator.
22. Locate and replace leaking fuel injector(s).
23. Locate and repair restriction in fuel return pipe.
24. Repair problem as necessary.

4.3L, 5.0L, 5.7L & 7.4L

1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
2. Disconnect injector harness connector at intake manifold. Turn ignition on. Using test light connected to ground, probe injector ignition feed circuits. If test light illuminates at all injector feed circuits, go to step 6 . If test light does not illuminate at all injector feed circuits, go to next step.
3. If test light illuminates for only some of the injector circuits, go to step 5 . If test light does not illuminate for any injector circuit, go to next step.
4. Check ECM I fuse (20-amp), located in underhood fuse block. If fuse is open, go to step 10 . If fuse is okay, go to step 11 .
5. Check for open in faulty injector feed circuit. After locating faulty circuit, go to step 12 .
6. Install injector test light to each injector circuit, one at a time. Crank engine. If injector test light flashes for each injector, check fuel injector(s). See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If injector test light does not flash for each injector circuit, go to next step.
7. If injector test light was on steady for any injector circuit, go to next step. If injector test light did not illuminate for any injector circuit, go to step 9 .
8. Install injector test light on faulty injector circuit. Turn ignition off. Disconnect VCM harness connector (Red). Turn ignition on. If injector test light is off, go to step 16 . If injector test light remains illuminated, go to step 13 .
9. Check for open or short to voltage in injector control circuit. If circuit is open or shorted, go to step 12 . If circuit is okay, go to step 14 .
10. Check for short to ground in injector control circuit. After locating short, go to step 12 .
11. Repair open or short to ground on all injector feed circuits. After repairs, go to step 17 .
12. Repair circuit as necessary. After repairs, go to step 17 .
13. Repair short to ground in injector control circuit. After repairs, go to step 17 .
14. Check terminal contact at VCM harness connector. If terminal contact is faulty, go to next step. If terminal contact is okay, go to step 16 .
15. Repair terminal contact as necessary. After repairs, go to step 17 .
16. Replace VCM. Perform VCM reprogramming procedures. After repairs, go to next step.
17. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, or starts and stalls, go to step 2 .
18. Allow engine to reach normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any other DTCs are set, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If no other DTCs are set, go to next step.
19. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional undiagnosed DTCs are set, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If additional DTCs are not present, system is okay.

1. Using scan tool, attempt to communicate with Alternative Fuel Electronic Control Unit (AF ECU). If communication is possible, go to next step. If communication is not possible and system check has been performed, go to step 7 .
2. Read and record any AF ECU DTCs. Go to next step.
3. Clear all AF ECU DTCs. Turn ignition off. Go to next step.
4. Start engine. Ensure vehicle is operating on CNG by noting if fuel indicator light (located on fuel gauge select switch) is off and Natural Gas Operation (NGO) in scan tool data is enabled. If vehicle is operating on CNG, go to next step. If vehicle does not start or is not operating on CNG, go to step 7 .
5. Using scan tool, select High Pressure Lock-Off (HPL) output control. Go to next step.
6. Monitor Fuel Pressure Sensor (FPS) data. While vehicle is operating on CNG, use scan tool to close HPL. If FPS data does not change, go to next step. When engine stalls or changes to gasoline operation, turn ignition off. Remove CNG fuse (20-amp) located in underhood fuse block. Slowly open fuel system fittings to vent remaining pressure.
7. Remove fuel tank cover. Close manual lock down screw on HPL by rotating Allen screw clockwise until fully seated. Go to next step.
8. Turn ignition off. Disconnect negative battery cable. Ensure vehicle is in a well ventilated area, away from sparks and flame. Go to next step.
9. Slowly open fuel line fitting at Low Pressure Lock-Off (LPL) inlet port. Do not remove fitting. Go to next step.
10. If fuel is not venting, relieve fuel line tension by pulling line away from LPL. Go to next step.
11. After fuel has stopped venting, slowly loosen fuel line fitting at High Pressure Regulator (HPR) inlet. Do not remove fitting. Fuel pressure relief is complete when fuel line at HPR inlet stops venting. After repair, replace "O" rings at all fittings that were loosened. Tighten all loosened fittings to specification. Open manual lock down screw counter-clockwise to fully seated position.

SPARK

1. If factory tachometer is connected to coil tachometer terminal, disconnect tachometer before performing tests. When removing spark plug wire from spark plug, twist and pull on boot. DO NOT pull on wire.
2. Using Spark Tester (J-26792), check for spark at each spark plug wire. Leave other wires connected while checking for spark. Check spark plug wire resistance on suspect wires. Ensure resistance is to specification. See appropriate SERVICE & ADJUSTMENT SPECIFICATIONS article.

IGNITION COIL POWER SOURCE

Turn ignition on. Check ignition positive voltage circuit of ignition control module for battery voltage. If battery voltage is not present, check fuse for ignition control module circuit. If fuse is not open, check for open in circuit between fuse and ignition control module.

IDLE SPEED & IGNITION TIMING (GASOLINE)

Ensure idle speed and ignition timing are set to specifications. For specifications and adjustment procedures, see appropriate ON-VEHICLE ADJUSTMENTS article.

SUMMARY

If no faults were found while performing basic diagnostic procedures, or no trouble codes (or only intermittent ones) were found while performing OBD system check, and driveability problems still exist, proceed to appropriate TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.