LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Pontiac >> 2002 >> Aztek AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P1635: 5-Volt Reference 1 Circuit >> Diagnostic Procedures
April 5, 2026: LEMON Manuals is launched! Read the announcement.

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 for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC, or within the parameters observed in the Freeze Frame/Failure Records. 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  13. If no, go to next step.
  4. Turn OFF the ignition. Disconnect the EGR valve electrical connector. Turn ON the ignition, with the engine OFF. Using a Digital Multimeter (DMM), measure voltage between the 5-volt reference circuit and engine ground. 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 EGR valve. Disconnect throttle position sensor. Using a DMM, measure voltage between the 5-volt reference 1 circuit and engine ground. Does the voltage measure 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 above components are disconnected, replace the component. Was a component replaced? If yes, go to step  13. If no, go to next step.
  8. Turn OFF the ignition. Disconnect the PCM. Check the 5-volt reference circuit for a short to ground or any sensor low reference circuit. If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  13. If no, go to step  12.
  9. Turn OFF the ignition. Disconnect the PCM. Turn ON the ignition, with the engine OFF. Check the following circuits for a short to voltage:
    • The 5-volt reference circuit.
    • The Manifold Absolute Pressure (MAP) sensor signal circuit.
    • The Fuel Tank Pressure (FTP) sensor signal circuit.

    If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  13. If no, go to step  12.

  10. Check for a short between the EGR control high circuit and the 5-volt reference circuit and repair as necessary. Did you find and correct the condition? If yes, go to step  13. If no, go to next step.
  11. Replace the EGR valve. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  13.
  12. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  13. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  14. 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.
scientia non olet · About LEMON Manuals