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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 92 (Engine Controls - Self-Diagnostics - 6.6L Diesel) >> Diagnostic Tests >> DTC P1635: 5-Volt Reference 1 Circuit >> 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. Observe the Freeze Frame/Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  3. Visually and physically inspect the ECM and engine grounds. Ensure that the grounds are clean and secure. If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  4. Turn OFF the ignition. Disconnect the Accelerator Pedal Position (APP) sensor electrical connector. Turn ON the ignition, with the engine OFF. Using a Digital Multimeter (DMM), measure the voltage between the 5-volt reference circuit of the APP sensor 1 or the APP sensor 3 and the engine ground. Does the voltage measure near 5 V? If yes, go to step  6. If no, go to next step.
  5. Does the voltage measure more than 5 V? If yes, go to step  9. If no, go to step  7.
  6. Reconnect the APP sensor. Disconnect the Fuel Rail Pressure (FRP) sensor. Using a DMM, measure the voltage between the FRP sensor 5-volt reference circuit and the engine ground. Does the voltage measure near 5 V? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to step  10.
  7. Monitor DMM while disconnecting the FRP sensor. If voltage changes when the sensor is disconnected, replace FRP sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  8. Turn OFF the ignition. Disconnect the ECM. Check the 5-volt reference circuit for the following conditions:
    • A short to ground.
    • A short to any low reference circuit.
    • A short to the fuel pressure regulator control circuit.
    • A short to the TCM MIL request circuit.
    • A short to the ignition 1 relay control circuit.

    If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  12. If no, go to step  11.

  9. Turn OFF the ignition. Disconnect the ECM. Turn ON the ignition, with the engine OFF. Check the 5-volt reference circuit for a short to voltage. If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  12. If no, go to step  11.
  10. Replace the APP sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  12.
  11. Replace the ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram ECM. See ENGINE CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  12. 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.
  13. 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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