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Home >> Pontiac >> 2001 >> 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. 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 TESTS. After performing powertrain diagnostic system check, go to next step.
  2. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data for this DTC and observe parameters. Turn ignition off for at least 30 seconds. Start engine. Operate vehicle within conditions for setting this DTC and as close to conditions recorded in Freeze Frame/Failure Records. Select DTC option, SPECIFIC DTC option, then enter this DTC on scan tool. If scan tool indicates that DTC set this ignition, go to next step. If scan tool does not indicate that DTC set this ignition, go to DIAGNOSTIC AIDS .
  3. Visually check for poor PCM or engine ground connections. See Figure. Repair as necessary. After repairs, go to step  13. If ground connections are okay, go to next step.
  4. Turn ignition off. Locate and disconnect A/C pressure sensor connector. See Figure. Turn ignition on. Using DVOM, measure voltage between ground and A/C pressure sensor connector terminal "B" (Gray wire). If voltage is approximately 5 volts, go to step  6. If voltage is not approximately 5 volts, go to next step.
  5. If voltage is more than 5 volts, go to step  9. If voltage is less than 5 volts, go to step  7.
  6. Reconnect A/C pressure sensor connector. Locate and disconnect FTP sensor. See Figure. Using DVOM, measure voltage between ground and FTP sensor connector terminal "C" (Gray/Black wire). If voltage is approximately 5 volts, go to DIAGNOSTIC AIDS . If voltage is not approximately 5 volts, go to step  10.
  7. Monitor DVOM voltage reading while disconnecting all other components using a 5-volt reference signal from PCM. See WIRING DIAGRAMS article for component identification. If voltage changes when one component is disconnected, replace that component. See REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to step  12. If voltage did not change after all components have been disconnected, go to next step.
  8. Turn ignition off. Locate PCM and disconnect connectors. See Figure. Check for short between PCM connector C1 terminal No. 45 (Gray wire) and sensor low reference (ground) circuits at PCM connectors. See WIRING DIAGRAMS article for terminal identification. See Figure. Repair as necessary. After repairs, go to step  12. If circuits are okay, go to step  11.
  9. Turn ignition off. Locate PCM and disconnect connectors. See Figure. Check for short between PCM connector C1 terminal No. 46 (Gray wire) and sensor low reference (ground) circuits at PCM connectors. See WIRING DIAGRAMS article for terminal identification. See Figure. Repair as necessary. After repairs, go to step  12. If circuits are okay, go to step  11.
  10. Replace A/C pressure sensor. See REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to step  12.
  11. Replace PCM. See REMOVAL, OVERHAUL & INSTALLATION - CARS article. After repairs, go to next step.
  12. Using scan tool, clear DTCs. Turn ignition off for at least 30 seconds. Start engine and allow it to reach normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step  2.
  13. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no undiagnosed DTCs are displayed, system is okay.
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