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Home >> Chevrolet >> 2001 >> Venture Base, Van Passenger >> Repair and Diagnosis >> External Pages >> Different car >> Section 233 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P1639: 5-Volt Reference "B" Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Pontiac Montana, 2003 Oldsmobile Silhouette, and 2003 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.
  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 INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.4L MONTANA, SILHOUETTE & VENTURE article.
  3. Turn ignition off. Disconnect the A/C pressure sensor connector. Connect a Digital Volt-Ohmmeter (DVOM) between the 5-volt reference and a good ground. Turn ignition on, with engine off. Does the voltage measure 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 with a DVOM. Is voltage within 4.8-5.2 volts? If yes, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.4L MONTANA, SILHOUETTE & VENTURE article. If no, go to step  12.
  5. Monitor the DVOM while disconnecting the FTP sensor. Does the voltage return to within 4.8-5.2 volts when FTP sensor is disconnected? If yes, go to step  8. If no, go to step  7.
  6. Turn ignition off. Leave the DVOM connected from step  3. Disconnect the PCM. Turn ignition on, with engine off. Does the voltage measure 0 V? If yes, go to step  14. If no, go to step  11.
  7. Turn ignition off. Disconnect PCM harness connector. 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 DVOM 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 FTP sensor. After replacing sensor, go to step  14.
  12. Replace A/C pressure sensor. After repairs, go to step  14.
  13. Replace PCM. See REMOVAL & INSTALLATION - MONTANA, SILHOUETTE & VENTURE article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  14. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate the 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.
  15. 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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