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Home >> Pontiac >> 2001 >> Firebird Base, 2D Convertible, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. If powertrain diagnostic system check was performed, go to next step. If powertrain diagnostic system check was not performed, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under DIAGNOSTIC SYSTEM CHECKS. After performing powertrain diagnostic system check, go to next step.
  2. Using scan tool, observe the FREEZE FRAME/FAILURE records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE records observed. If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, go to DIAGNOSTIC AIDS .
  3. Inspect PCM and engine grounds. Ensure that grounds are clean and secure. Repair as necessary. After repairs, go to step  12. If no problem is found, go to next step.
  4. Turn ignition off. Disconnect A/C pressure sensor connector. Turn ignition on, with engine off. Using a DVOM, check voltage between a known-good ground and A/C pressure sensor connector terminal "B" (Light Blue/black wire). If voltage reading is about 5 volts, go to step  10. If voltage reading is not about 5 volts, go to next step.
  5. If voltage reading is more than 5 volts, go to next step. If voltage reading is not more than 5 volts, go to step  7.
  6. Turn ignition off. Disconnect PCM connectors. Check for short to voltage on Light Blue/Black wire between A/C pressure sensor and PCM. After repairs, go to step  12. If circuit is okay, go to step  11.
  7. Check continuity between the A/C pressure sensor connector terminals "B" (Light Blue/Black wire) and "C" (Red/Black wire). If continuity exists, go to next step. If continuity does not exists, go to step  9.
  8. Leave ignition off. Check continuity between a known-good chassis ground and A/C pressure sensor connector terminal "B" (Light Blue/Black wire). If continuity exists, go to step  11. If continuity does not exist, go to next step.
  9. Repair Light Blue/Black wire for short to chassis ground or short to Red/Black wire in A/C pressure sensor circuit. After repairs, go to step  12.
  10. Replace A/C pressure sensor. After replacing sensor, go to step  12.
  11. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE PROGRAMMING  under PROGRAMMING. After replacing PCM, go to next step.
  12. Using scan tool, observe the stored information and Capture Info. If any undiagnosed DTCs are displayed, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTC are displayed, system is okay.
  13. Using scan tool, observe the stored information and Capture Info. If DTC resets, go to step  2. If DTC does not reset, system is okay.
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