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Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.0L AURORA article.
  2. Turn ignition on, with engine off. Using scan tool, observe DTC information. Does the scan tool display DTC P0230, P0335, P0340, P0385, P0403, P0404, P1404, P0601, P0602, P0603, P0604, P1621, P1630, P1631? If yes, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.0L AURORA article. If no DTC(s) are set, go to next step.
  3. Inspect the fuse that supplies ignition voltage to the ignition coil cassettes. Is fuse open? If yes, go to ELECTRONIC IGNITION SYSTEM DIAGNOSIS  under IGNITION SYSTEMS. If no, go to next step.
  4. Using scan tool, command fuel pump on. Does fuel pump turn on? If yes, go to next step. If no, go to FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS  under FUEL SYSTEMS.
  5. Turn ignition off. Install Fuel Pressure Gauge (J-34730-1A). See FUEL SYSTEM PRESSURE RELEASE  under FUEL SYSTEMS. Turn ignition on, with engine off. Using scan tool, command the fuel pump on. Is fuel pressure within 41-47 psi (284-325 kPa) while fuel pump is operating? If yes, go to next step. If no, go to FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS  under FUEL SYSTEMS.
  6. Check the following:
    • Check for collapsed air intake duct.
    • Check for restricted air filter element.
    • Check spark plugs for being gas or coolant fouled. If spark plugs are fouled, determine cause of condition.
    • Check engine mechanical condition, such as worn timing chain and gears, low compression, etc.
    • Restricted exhaust system.
    • Faulty Manifold Absolute Pressure (MAP) sensor.
    • Faulty Engine Coolant Temperature (ECT) sensor.

    If any problems are found, repair as necessary. After repairs, go to next step. If no problems are found, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.0L AURORA article.

  7. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start, go to step  2 .
  8. Allow engine to idle. Ensure engine is at normal operating range. Using scan tool, observe DTC information. If any DTCs are set, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.0L AURORA article. If scan tool does not display any DTCs, system is okay.
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