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Home >> Pontiac >> 2002 >> Firebird Base, 2D Convertible, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 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. 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  12. If no, go to next step.
  4. Turn the ignition OFF. Disconnect the AC pressure sensor electrical connector. Connect a Digital Multimeter (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 step  10. If no, go to next step.
  5. Does the voltage measure more than 5 V? If yes, go to next step. If no, go to step  7.
  6. Turn OFF the ignition. Disconnect the PCM and check for a short to voltage on the 5-volt reference circuit and repair as necessary. Did you find and repair a condition? If yes, go to step  12. If no, go to step  11.
    7. NOTE: The ignition must me turned OFF for this test.
  7. Turn OFF the ignition. Using a DMM check for continuity between the 5-volt reference circuit and the low reference circuit at the A/C pressure sensor connector. Is the resistance infinite? If yes, go to next step. If no, go to step  9.
  8. Leave the ignition OFF. Using a DMM check for continuity between the 5-volt reference circuit and a good chassis ground. Is the resistance infinite? If yes, go to step  11. If no, go to next step.
  9. Repair the circuit for a short to chassis ground or a short to A/C pressure sensor low reference. After repairs, go to step  12.
  10. Replace the AC pressure sensor. See appropriate MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. 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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