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Home >> GMC >> 2002 >> Jimmy 2D Utility, Part Time, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 4.3L >> Diagnostic Tests >> DTC P1635: 5-Volt Reference 1 Circuit >> Diagnostic Procedures

Diagnostic Procedures

  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. Did 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 PCM 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 Throttle Position (TP) 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 and the engine ground. Is voltage near 5 V? If yes, go to step  6. If no, go to next step.
  5. Is the voltage more than 5 V? If yes, go to step  9. If no, go to step  7.
  6. Reconnect the TP sensor. Disconnect the Manifold Absolute Pressure (MAP) sensor. Using a DMM, measure the voltage between the 5-volt reference 1 circuit and the engine ground. Is the voltage near 5 V? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to step  10.
  7. Monitor the DMM while disconnecting all other devices connected to a 5-volt reference circuit one at a time. If the voltage changes when one of the above components are disconnected, replace the component. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Was a component replaced? If yes, go to step  12. If no, go to next step.
  8. Turn OFF the ignition. Disconnect the PCM. Check the 5-volt reference circuit for a short to ground or any sensor low reference 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 PCM. Turn ON the ignition, with the engine OFF. Check the following circuits for a short to voltage:
    • The 5-volt reference circuit.
    • The manifold absolute pressure MAP sensor signal 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.

  10. Replace the TP sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  12.
  11. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN 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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