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Home >> Pontiac >> 2002 >> Firebird Formula, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 5.7L >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Diagnostic Procedures

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 data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  3. Visually and physically inspect the PCM and engine grounds. Ensure that the grounds are clean and secure. If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  4. Turn the ignition OFF. Disconnect the AC pressure sensor electrical connector. Connect a Digital Multimeter (DMM) between the 5-volt reference and a good ground. Turn the ignition ON, with the engine OFF. Does the voltage measure near 5 V? If yes, go to step  6. If no, go to next step.
  5. Does the voltage measure more than 5 V? If yes, go to step  9. If no, go to step  7.
  6. Reconnect AC pressure sensor. Disconnect FTP sensor. Using a DMM, measure voltage between the 5-volt reference 1 circuit and a good ground. Is voltage near 5 V? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to step  10.
  7. Monitor DMM while disconnecting all other devices connected to 5-volt reference circuit one at a time. If voltage changes when one of the components are disconnected, replace the component. Was a component replaced? If yes, go to step  12. If no, go to next step.
  8. Turn OFF the ignition. Disconnect the PCM. Test the 5-volt reference circuit for a short to ground or any sensor low reference circuit. If a problem is found, repair as necessary. Was a problem found? If yes, go to step  12. If no, go to step  11.
  9. Turn OFF the ignition. Disconnect the PCM. Turn ON the ignition, with the engine OFF. Test the 5-volt reference circuit and the FTP sensor signal circuit for a short to voltage. If a problem is found, repair as necessary. Was a problem found? If yes, go to step  12. If no, go to step  11.
  10. Replace the AC pressure sensor. After repairs, go to step  12.
  11. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  12. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool. Idle the engine at the normal operating temperature. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool. Operate the vehicle within the Conditions for Running DTC, if applicable. Does the scan tool indicate that this test ran and passed? If yes, go to next step. If no, go to step  2.
  13. 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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