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Home >> Pontiac >> 2001 >> Aztek Base, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P1635: 5-Volt Reference "A" Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
  2. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running this DTC or as close to FREEZE FRAME/FAILURE RECORDS data observed. See CODE ENABLE CRITERIA . If DTC fails this ignition, go to next step. If DTC does not fail this ignition, problem is intermittent.
  3. Visually and physically inspect PCM and engine grounds. See WIRING DIAGRAMS article. Ensure that grounds are clean and secure. If a problem is found, 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 harness connector. Turn ignition on, with engine off. Using a DVOM, check voltage between chassis ground and EGR harness connector terminal "D" (Gray wire). See Figure. 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 greater than 5 volts, go to step  9. If voltage reading is not greater than 5 volts, go to step  7.
  6. Reconnect EGR valve harness connector. Disconnect throttle position sensor harness connector. Using DVOM, check voltage between chassis ground and TP sensor harness connector harness connector terminal "A" (Gray wire). If voltage reading is about 5 volts, problem is intermittent. If voltage reading is not about 5 volts, go to step  10.
  7. Monitor DVOM while disconnecting all other devices (A/C Pressure, ECT, EGR, FTP, IAT and MAP sensors) connected to PCM 5-volt reference circuit one at a time. If voltage changes when one of the components is disconnected, replace affected component. After replacing affected component, go to step  13. If voltage does not change when one of the components is disconnected, go to next step.
  8. Turn ignition off. Disconnect PCM harness connector. Check the 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 no problem is found, go to step  12.
  9. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Check for short to voltage or short to 5-volt reference circuit in MAP and FTP sensor signal circuits. Repair as necessary. After repairs, go to step  13. If circuits are okay, go to step  12.
  10. Turn ignition off. Check for short between EGR control high circuit (Red wire) and 5-volt reference circuit (Gray wire). 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, go to step  13.
  12. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  13. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running this DTC. See CODE ENABLE CRITERIA . If DTC runs and passes, go to next step. If DTC resets, go to step  2.
  14. Using a scan tool, observe stored information and CAPTURE INFO. If scan tool displayed any undiagnosed DTCs, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are displayed, system is okay.
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