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Home >> Chevrolet >> 2001 >> Venture Base, Van Passenger >> Repair and Diagnosis >> External Pages >> Different car >> Section 79 (Engine Controls - Self-Diagnostics - 4.0L) >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. 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, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Observe the Freeze Frame/Failure Records data for this DTC. Turn the ignition OFF 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 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  17. If no, go to next step.
  4. Turn the ignition OFF. Disconnect the A/C pressure sensor connector. Connect a DMM between the 5-volt reference and a good ground. Turn the ignition ON, with the engine OFF. Does the voltage measure near 5 V? If yes, go to next step. If no, go to step  6.
  5. Turn OFF the ignition. Reconnect the A/C pressure sensor. Disconnect the Fuel Tank Pressure (FTP) sensor. Connect a DMM between the 5-volt reference at the FTP sensor connector and a good ground. Turn the ignition ON, with the engine OFF. Does the voltage measure near 5 V? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to step  13.
  6. Does the voltage measure more than 5 V? If yes, go to next step. If no, go to step  8.
  7. Turn the ignition OFF. Leave the DMM connected from step  4. Disconnect the PCM. Turn the ignition ON, with the engine OFF. Does the voltage measure 0 V? If yes, go to step  15. If no, go to step  12.
  8. Turn the ignition OFF. Leave the DMM connected from step  4. Disconnect the FTP sensor. Turn the ignition ON, with the engine OFF. Does the voltage measure near 5 V? If yes, go to step  14. If no, go to next step.
    9. NOTE: The ignition must me turned OFF for this test.
  9. Turn the ignition OFF. Using a DMM check for continuity between the 5-volt reference circuit and the low reference circuit of the A/C pressure sensor or the FTP sensor. Is the resistance at infinity or OL? If yes, go to next step. If no, go to step  11.
  10. Leave the ignition OFF. Using a DMM check for continuity between the 5-volt reference circuit and a good chassis ground. Is the resistance at infinity or OL? If yes, go to step  15. If no, go to next step.
  11. Repair the circuit for a short to chassis ground or a short to the FTP or A/C pressure sensor low reference circuits. After repairs, go to step  17.
  12. Locate and repair the short to voltage in the 5-volt reference circuit or the FTP signal circuit. After repairs, go to step  17.
  13. Replace the A/C pressure sensor. After repairs, go to step  17.
  14. Replace the fuel tank pressure FTP sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  17.
  15. Check the 5-volt reference circuit for an open, short to chassis ground or poor connection at the PCM. Did you find a problem? If yes, go to step  17. If no, go to next step.
  16. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  17. Use the scan tool in order to clear the DTCs. 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. With a scan tool, observe the stored information, Capture Info. 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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