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Home >> Chevrolet >> 2001 >> Venture Base, Van Passenger >> Repair and Diagnosis >> External Pages >> Different car >> Section 246 (Engine Controls Self-Diagnostics - 3.1L Engine) >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit (Century) >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. 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 Test. See CONDITIONS FOR RUNNING TEST . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition cycle? 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) 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 pressure sensor to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to next step. If no, go to step  5.
  4. Connect the A/C pressure sensor. Disconnect the Fuel Tank Pressure (FTP) sensor. Measure the voltage from the 5-volt reference circuit of the FTP sensor to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step  12.
  5. Is the voltage measured in the previous step more than 5.2 volts? If yes, go to step  8. If no, go to next step.
  6. Monitor the DMM while disconnecting the FTP sensor. Does the voltage return to 4.8-5.2 volts when the FTP sensor is disconnected? If yes, go to step  11. If no, go to next step.
  7. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Test the 5-volt reference circuit for a short to ground or any sensor low reference circuit. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
  8. Monitor the DMM while disconnecting the FTP sensor. Does the voltage return to 4.8-5.2 volts when the FTP sensor is disconnected? If yes, go to step  10. If no, go to next step.
  9. Test all 5-volt reference circuits for a short to voltage. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
  10. Test the FTP sensor signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
  11. Replace the FTP sensor. After repair, go to step  14.
  12. Replace the A/C pressure sensor. See REFRIGERANT PRESSURE SENSOR in appropriate AIR CONDITIONING & HEATING article. After repair, go to step  14.
  13. 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.
  14. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within Conditions For Running Test. See CONDITIONS FOR RUNNING TEST . Did the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  15. Using the scan tool, observe the stored information in CAPTURE INFO. Does 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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