LEMON Manuals: Even more car manuals for everyone
Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 85 (Engine Controls - Self-Diagnostics - 8.1L) >> Diagnostic Tests >> DTC P1635: 5-Volt Reference 1 Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 GMC Savana Special, 2002 GMC Savana Camper Special, and 2002 GMC Savana. 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. Install a scan tool. Start the engine. Idle the engine for 2 minutes. Monitor the DTCs using a scan tool. Did both DTCs P1635 and P1639 fail this ignition cycle? If yes, go to step  5. If no, go to next step.
  3. Did DTC P1635 fail this ignition cycle? If yes, go to step  9. If no, go to next step.
    4. NOTE: If DTCs P1635 and P1639 set, go to next step. If only DTC P1635 sets, go to step  9.
  4. Turn ON the ignition, with the engine OFF. Review the Freeze Frame/Failure Records data for this DTC and observe the parameters. Turn OFF the ignition for 15 seconds. Start the engine. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running DTC. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool. You will have to select DTC P1635 and P1639 to determine if both DTCs set at the same time. Does the scan tool indicate that DTC P1635 or P1639 set this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  5. While idling the engine, monitor the voltages for the following sensors:
    • The fuel level sensor.
    • The FTP sensor.
    • The EGR pintle position sensor.
    • The TP sensor.
    • The MAP sensor.

    Does the scan tool display any of the voltages at or above 5 V? If yes, go to step  16. If no, go to next step.

  6. Turn OFF the engine, leaving the ignition ON. Monitor the following voltages using a scan tool:
    • MAP sensor.
    • TP sensor.
    • EGR pintle position sensor.
    • FTP sensor.
    • Fuel level sensor.

    Enable the fuel pump using the scan tool. Does any of the voltages increase when the fuel pump was turned ON? If yes, go to step  11. If no, go to next step.

  7. Turn OFF the ignition. Disconnect the PCM harness connector C1. Turn ON the ignition, leaving the engine OFF. Connect the Digital Multimeter (DMM) to ground. Probe the other lead of the DMM to each 5-volt reference circuit at the PCM harness connector for the following components:
    • The MAP sensor.
    • The EGR valve.
    • The FTP sensor.
    • The TP sensor.

    Do any of the circuits measure more than 5.1 V? If yes, go to step  12. If no, go to next step.

    8. NOTE: For detailed circuit information, see WIRING DIAGRAMS article.
  8. Before proceeding, remove the following fuses:
    • Ignition 0 fuse located in the left Instrument Panel (IP) electrical center.
    • ECM 1 fuse located in the underhood electrical center.
    • ECM B fuse located in the underhood electrical center.

    Disconnect the following components:

    • The MAP sensor.
    • The TP sensor.
    • The EGR valve.
    • The fuel level sensor.
    • The FTP sensor.

    Test continuity from each 5-volt reference circuit to all other PCM circuits at the PCM harness connector using the DMM. Example: probe one lead to the MAP sensor 5-volt reference at the PCM harness connector circuit and probe the other lead to each terminal at the PCM harness connector. This must be performed for each 5-volt reference circuit. Do any of the circuits indicate a resistance of 0-2 ohms? If yes, go to step  13. If no, go to step  15.

    9. NOTE: For detailed circuit information, see WIRING DIAGRAMS article.
  9. Turn OFF the ignition. Disconnect the PCM connector C1. Connect the test lamp to battery voltage. Probe the test lamp to the PCM connector 5-volt reference circuits for the following components:
    • The MAP sensor.
    • The EGR valve.

    Does the test lamp illuminate for any of the circuits? If yes, go to step  14. If no, go to next step.

  10. Test continuity from each 5-volt reference circuit to all other PCM circuits at the PCM harness connector using the DMM. Example: probe one lead to the MAP sensor 5-volt reference at the PCM harness connector circuit and probe the other lead to each terminal at the PCM harness connector. This must be performed for each 5-volt reference circuit. Do any of the circuits indicate a resistance of 0-2 ohms? If yes, go to step  13. If no, go to step  15.
  11. Repair the short between the fuel pump circuit and the appropriate 5-volt reference circuit or signal circuit. After repairs, go to step  17.
  12. Repair the short to voltage on the appropriate 5-volt reference circuit. After repairs, go to step  17.
  13. Repair the short between the appropriate 5-volt reference circuit and the PCM circuit that had continuity. After repairs, go to step  17.
  14. Repair the short to ground on the appropriate 5-volt reference circuit. After repairs, go to step  17.
  15. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to step  17.
  16. Repair the short to voltage on the appropriate signal circuit. After repairs, go to next step.
  17. 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.
  18. 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.
scientia non olet · About LEMON Manuals