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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 81 (Engine Controls - Self-Diagnostics - 4.8L, 5.3L & 6.0L) >> Diagnostic Tests >> DTC P1172: Fuel Transfer With Secondary Pump >> Diagnostic Procedures

Diagnostic Procedures

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  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: The fuel level must be between 25-50 percent to perform this diagnostic procedure. If the fuel level is not within this range, misdiagnosis will occur.
  2. Turn OFF the ignition. Remove the secondary fuel pump relay. Turn ON the ignition, with the engine OFF. Probe the supply voltage circuit of the secondary fuel pump relay, coil side, with a test lamp connected to a good ground. Command the fuel pump ON with a scan tool. Does the test lamp illuminate when the fuel pump is commanded ON? If yes, go to next step. If no, go to step  22.
  3. Probe the ignition 1 voltage circuit of the secondary fuel pump relay, switch side, with a test lamp connected to a good ground. Is the test lamp illuminated? If yes, go to next step. If no, go to step  12.
  4. Jumper the ignition 1 voltage circuit to the secondary fuel pump supply voltage circuit, at the secondary fuel pump relay harness connector. Does the secondary fuel pump turn ON? If yes, go to next step. If no, go to step  16.
  5. Turn OFF the ignition. Remove the jumper wire from the secondary fuel pump relay harness connector. Turn ON the ignition, with the engine OFF. Monitor the rear fuel level voltage with a scan tool. Is the rear fuel level sensor voltage above 1 V? If yes, go to step  7. If no, go to next step.
  6. Add 5 gal (19 L) of fuel to the fuel tank. After adding fuel, go to next step.
  7. Turn OFF the ignition. Jumper the ignition voltage circuit to the secondary fuel pump supply voltage circuit, at the secondary fuel pump relay harness connector. Turn ON the ignition, with the engine OFF. Monitor the rear fuel level sensor voltage with a scan tool. Does the rear fuel level sensor voltage decrease as the secondary fuel pump is operating? If yes, go to next step. If no, go to step  18.
  8. Turn OFF the ignition. Remove the jumper wire from the secondary fuel pump relay harness connector. Turn ON the ignition, with the engine OFF. Probe the secondary fuel pump relay control circuit with a test lamp connected to a battery voltage. Does the test lamp illuminate? If yes, go to step  23. If no, go to next step.
  9. Probe the secondary fuel pump relay control circuit with a test lamp connected to a good ground. Does the test lamp illuminate? If yes, go to step  27. If no, go to next step.
  10. Turn OFF the ignition. Jumper the following secondary fuel pump relay switch circuits, from the secondary fuel pump relay, to the secondary fuel pump relay harness connector:
    • Ignition 1 voltage circuit.
    • Secondary fuel pump supply voltage circuit.

    Jumper the supply voltage terminal of the secondary fuel pump relay to battery voltage. Turn ON the ignition, with the engine OFF. Jumper the control terminal of the secondary fuel pump relay to a good ground. Does the secondary fuel pump turn ON when the fuel pump relay control terminal is grounded? If yes, go to next step. If no, go to step  19.

  11. Test the secondary fuel pump relay control circuit for an open. Did you find and correct the condition? If yes, go to step  31. If no, go to step  21.
  12. Inspect the ENG 1 fuse. Is the ENG 1 fuse open? If yes, go to next step. If no, go to step  25.
  13. Test the ignition 1 voltage circuit of the secondary fuel pump relay for a short to ground. Did you find and correct the condition? If yes, go to step  31. If no, go to next step.
  14. Test the voltage supply circuit of the secondary fuel pump for a short to ground. Did you find and correct the condition? If yes, go to step  31. If no, go to next step.
  15. Turn OFF the ignition. Install a new fuse. Jumper the ignition voltage circuit to the secondary fuel pump supply voltage circuit, at the secondary fuel pump relay harness connector. Turn ON the ignition, with the engine OFF. Inspect the ENG 1 fuse. Is the fuse open? If yes, go to step  29. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  16. Lower the rear fuel tank. Disconnect the secondary fuel pump harness connector. Probe the voltage supply circuit of the secondary fuel pump with a test lamp connected to a good ground. Is the test lamp illuminated? If yes, go to next step. If no, go to step  26.
  17. Probe the ground circuit of the secondary fuel pump with a test lamp connected to battery voltage. Does the test lamp illuminate? If yes, go to step  20. If no, go to step  24.
  18. Inspect the fuel line between the primary and secondary fuel tanks for a restriction. Did you find and correct the condition? If yes, go to step  31. If no, go to step  29.
  19. Inspect for poor connections at the harness connector of the secondary fuel pump relay. Did you find and correct the condition? If yes, go to step  31. If no, go to step  28.
  20. Inspect for poor connections at the harness connector of the secondary fuel pump. Did you find and correct the condition? If yes, go to step  31. If no, go to step  29.
  21. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step  31. If no, go to step  30.
  22. Repair the open supply voltage circuit of the secondary fuel pump relay. After repairs, go to step  31.
  23. Repair the short to ground in the control circuit of the secondary fuel pump relay. After repairs, go to step  31.
  24. Repair the open ground circuit of the secondary fuel pump. After repairs, go to step  31.
  25. Repair the open ignition voltage circuit of the secondary fuel pump relay. After repairs, go to step  31.
  26. Repair the open supply voltage circuit of the secondary fuel pump. After repairs, go to step  31.
  27. Repair the short to voltage on the control circuit of the secondary fuel pump relay. After repairs, go to step  31.
  28. Replace the secondary fuel pump relay. After repairs, go to step  31.
  29. Replace the rear fuel level sensor assembly. After repairs, go to step  31.
  30. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  31. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  32. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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