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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 87 (Engine Controls - Self-Diagnostics - 6.6L Diesel) >> Diagnostic Tests >> DTC P1172: Fuel Transfer With Secondary Pump >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  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 in order to perform this diagnostic procedure. If the fuel level is not within this range, misdiagnosis will occur.
  2. Turn ON the ignition, with the engine OFF. Command the fuel pump ON and OFF with a scan tool. Does the fuel pump relay click as you command the fuel pump ON and OFF? If yes, go to step  8. If no, go to next step.
  3. Remove the fuel pump relay from the underhood electrical center. Probe the ground circuit of the fuel pump relay with a test lamp connected to battery voltage. Is the test lamp illuminated? If yes, go to next step. If no, go to step  20.
  4. Probe the control circuit of the fuel pump relay with a test lamp connected to a good ground. Command the fuel pump ON and OFF with a scan tool. Does the test lamp turn ON and OFF? If yes, go to step  17. If no, go to next step.
  5. Does the test lamp remain illuminated with each command? If yes, go to next step. If no, go to step  7.
  6. Test the control circuit of the fuel pump relay for a short to battery voltage. Did you find and correct the condition? If yes, go to step  26. If no, go to step  25.
  7. Test the control circuit of the fuel pump relay for an open or a short to ground. Did you find and correct the condition? If yes, go to step  26. If no, go to step  19.
  8. Command the fuel pump ON with a scan tool. Does the fuel pump run? If yes, go to step  13. If no, go to next step.
  9. Remove the fuel pump relay from the underhood electrical center. Turn ON the ignition, with the engine OFF. Probe the ignition 1 voltage circuit of the fuel pump relay 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  22.
  10. Probe the fuel pump supply circuit with a test lamp connected to battery voltage. Does the test lamp blink? If yes, go to step  17. If no, go to next step.
  11. Test the fuel pump supply circuit for an open. Did you find and correct the condition? If yes, go to step  26. If no, go to next step.
  12. Probe the ground circuit of the fuel pump with a test lamp connected to battery voltage. Is the test lamp illuminated? If yes, go to step  18. If no, go to step  21.
  13. Monitor the rear fuel level sensor voltage with a scan tool. Is the rear fuel level sensor voltage above 1 V? If yes, go to step  15. If no, go to next step.
  14. Add 5 Gal (19 L) of fuel to the fuel tank. Go to next step.
  15. Turn OFF the ignition. Remove the fuel pump relay from the underhood electrical center. Jumper the ignition 1 voltage circuit to the fuel pump supply voltage circuit, at the underhood electrical center. 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 fuel pump is operating? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to next step.
  16. Inspect for the following conditions:
    • A restriction in the fuel lines between the front and rear fuel tanks.
    • The rear fuel sender for a restriction.

    Did you find and correct the condition? If yes, go to step  26. If no, go to step  24.

  17. Inspect for poor connections at the harness connector of the fuel pump relay. Did you find and correct the condition? If yes, go to step  26. If no, go to step  23.
  18. Inspect for poor connections at the harness connector of the fuel pump. Did you find and correct the condition? If yes, go to step  26. If no, go to step  24.
  19. Inspect for poor connections at the harness connector of the ECM. Did you find and correct the condition? If yes, go to step  26. If no, go to step  25.
  20. Repair the open ground circuit of the fuel pump relay. After repairs, go to step  26.
  21. Repair the open ground circuit of the fuel pump. After repairs, go to step  26.
  22. Repair the open ignition 1 voltage circuit of the fuel pump relay. After repairs, go to step  26.
  23. Replace the fuel pump relay. After repairs, go to step  26.
  24. Replace the fuel pump. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  26.
  25. Replace the ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram ECM. See ENGINE CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  26. 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.
  27. 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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