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Home >> Chevrolet >> 2001 >> Venture Base, Van Passenger >> Repair and Diagnosis >> External Pages >> Different car >> Section 68 (Engine Control System Self-Diagnostics - 3.8L) >> Diagnostic Tests >> DTC P1635: 5-Volt Reference Circuit "A" Or No. 1 >> Diagnostic Procedures

Diagnostic Procedures

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  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS . After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within Conditions for Running DTC or as close to FREEZE FRAME/FAILURE RECORDS data as possible. 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. Was a problem found? If yes, go to step  13. If no, go to next step.
  4. Turn ignition off. Disconnect EGR valve connector. Turn ignition on, engine off. Using DMM, measure voltage between the 5-volt reference circuit and engine ground. Is voltage near 5 volts? If yes, go to step  6. If no, go to next step.
  5. Is voltage more than 5 volts? If yes, go to step  9. If no, go to step  7.
  6. Reconnect EGR valve. Disconnect TP sensor. Using DMM, measure voltage between the 5-volt reference circuit and engine ground. Is voltage near 5 volts? 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 component is disconnected, replace that component. Was a component replaced? If yes, go to step  13. If no, go to next step.
  8. Turn ignition off. Disconnect PCM. Check 5-volt reference circuit for short to ground or any sensor low reference circuit. If problem was found, repair as necessary. Was a problem found? If yes, go to step  13. If no, go to step  12.
  9. Turn ignition off. Disconnect PCM. Turn ignition on, engine off. Check the following circuits for a short to voltage:
    • 5-volt reference circuit.
    • Fuel Tank Pressure (FTP) sensor signal circuit (if applicable).
    • Manifold Absolute Pressure (MAP) sensor signal circuit.

    If a problem is found, repair as necessary. Was a problem found? 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 a condition? If yes, go to step  13. If no, go to next step.
  11. Replace EGR valve. After repairs, go to step  13.
  12. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  13. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within Conditions for Running DTC. Does DTC run and pass? If yes, go to next step. If no, go to step  2.
  14. Using scan tool, observe stored information. Does scan tool displays any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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