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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 P1635: 5-Volt Reference 1 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 data observed. If DTC fails this ignition cycle, go to next step. If DTC does not fail this ignition cycle, go to DIAGNOSTIC AIDS .
  3. Check PCM and engine grounds. Ensure that grounds are clean and secure. Repair as necessary. After repairs, go to step  13. If no problem is found, go to next step.
  4. Turn ignition off. Disconnect EGR valve connector. Turn ignition on, with engine off. Using a DVOM, check voltage between chassis ground and EGR connector terminal "D" (Gray wire). If voltage reading is about 5 volts, go to step  6. If voltage reading is not about 5 volts, go to next step.
  5. If voltage reading is more than 5 volts, go to step  9. If voltage reading is not more than 5 volts, go to step  7.
  6. Reconnect EGR valve connector. Disconnect MAP sensor connector. Using DVOM, check voltage between engine ground and MAP sensor connector terminal "C" (Gray wire). If voltage reading is about 5 volts, go to DIAGNOSTIC AIDS . If voltage reading is not about 5 volts, go to step  10.
  7. Monitor DVOM while disconnecting all other devices connected to 5-volt reference circuit one at a time. See WIRING DIAGRAMS. If voltage changes when one of the components are disconnected, replace affected component. After replacing component, go to step  13. If no problem is found, go to next step.
  8. Turn ignition off. Disconnect PCM connector. Check 5-volt reference circuit for a short to ground or any sensor low reference circuit. Repair as necessary. After repairs, go to step  13. If circuits are okay, go to step  12.
  9. Turn ignition off. Disconnect PCM connectors. Turn ignition on, with engine off. Check for short to voltage in Light Green wire between MAP sensor and PCM. Repair as necessary. After repairs, go to step  13. If circuit is okay, go to step  12.
  10. Check for short between EGR control high circuit and 5-volt reference circuit. Repair as necessary. After repairs, go to step  13. If circuits are okay, go to next step.
  11. Replace EGR valve. After replacing EGR valve, so to step  13.
  12. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE PROGRAMMING  under PROGRAMMING. After replacing PCM, go to next step.
  13. 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.
  14. 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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