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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 379 (Engine Controls Self-Diagnostics - 3.4L) >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  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 for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running. See CONDITIONS FOR RUNNING . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  3. Turn ignition switch to OFF position. Disconnect the Air Conditioning (A/C) refrigerant pressure sensor harness connector. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the 5-volt reference circuit of the A/C refrigerant pressure sensor to a good ground using a DMM. Is the voltage 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 switch to OFF position. Disconnect the PCM harness connectors. Turn ignition switch to RUN position, engine OFF. Measure the voltage from the 5-volt reference circuit of the A/C refrigerant pressure sensor to a good ground using a DMM. Is the voltage more than zero volts? If yes, go to next step. If no, go to step  7.
  6. Check the 5-volt reference circuit for a short to voltage. Repair as necessary. After repair, go to step  11.
  7. Check 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 switch to OFF position. Disconnect the PCM harness connectors. Check 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 the A/C refrigerant pressure sensor. After repair, go to step  11.
  10. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  11. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position. Start the engine. Operate the vehicle within the Conditions For Running. See CONDITIONS FOR RUNNING . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  12. Using the scan tool, observe the stored information in 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 at this time.
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