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Home >> Buick >> 2002 >> Century Custom >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.1L Engine >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC or as close to the Freeze Frame/Failure Records data that you observed. See CONDITIONS FOR RUNNING DTC . Does the DTC fail this ignition? If yes, go to next step. If no, go to INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  3. 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 ignition off. Disconnect the A/C pressure sensor connector. Sensor is located on refrigerant line, above the condenser. Connect a Digital Multimeter (DMM) between the 5-volt reference and a good ground. Turn ignition on, with engine off. Does the voltage measure about 5 volts? If yes, go to step  10. If no, go to next step.
  5. Does the voltage measure more than 5 volts? If yes, go to next step. If no, go to step  7.
  6. Turn ignition off. Disconnect the PCM. Inspect for a short to voltage on the 5-volt reference circuit. Repair as necessary. Did you find and repair a problem? If yes, go to step  12. If no, go to step  11.
  7. Turn ignition off. Using a DMM inspect for continuity between the 5-volt reference circuit and low reference circuit at the A/C pressure sensor connector. Does the resistance measure infinity or OL? If yes, go to next step. If no, go to step  9.
  8. Leave ignition off. Using a DMM, inspect for continuity between the 5-volt reference circuit and a good chassis ground. Does the resistance measure infinity or OL? 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 A/C pressure sensor. After repairs, go to step  12.
  11. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  12. Use the scan tool in order to clear the DTCs. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  13. Using scan tool, observe stored information and 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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