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Home >> Pontiac >> 2003 >> Aztek AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Diagnostic Procedures
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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 for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running DTC or within the parameters observed in the Freeze Frame/Failure Records. See CONDITIONS FOR RUNNING DTC . Does the DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  3. Turn ignition off. Disconnect the A/C refrigerant pressure sensor. Turn ignition on, with engine off. Measure the voltage from the 5-volt reference circuit of the A/C refrigerant pressure sensor to a good ground with a DVOM. Is the voltage within 4.8-5.2 volts? If yes, go to step  9. If no, go to next step.
  4. Is the voltage measured in the previous step more than 5.2 volts? If yes, go to next step. If no, go to step  8.
  5. Turn ignition off. Disconnect the PCM. Turn ignition on, with engine off. Measure the voltage from the 5-volt reference circuit of the A/C refrigerant pressure sensor to a good ground with a DVOM. Is the voltage more zero volts? If yes, go to next step. If no, go to step  7.
  6. Test the 5-volt reference circuit for a short to voltage. Repair as necessary. After repairs, go to step  11.
  7. Test the 5-volt reference circuit for a short to any other circuit within the harness to the PCM. Did you find and correct the condition? If yes, go to step  11. If no, go to step  10.
  8. Turn ignition off. Disconnect the PCM. Test the 5-volt reference circuit for a short to ground or a short to any other circuit within the harness to the PCM. Did you find and correct the condition? If yes, go to step  11. If no, go to step  10.
  9. Replace A/C refrigerant pressure sensor. After replacing sensor, go to step  11.
  10. Replace PCM. See REMOVAL & INSTALLATION - AZTEC & RENDEZVOUS article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  11. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions for Running DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  12. 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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