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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1998 (Engine Controls And Fuel - 3.6L (LCS) - DTC P0638 To DTC P2229) >> DTC P0685, P0686, P0687, P0689, or P0690 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, open the hood to disable the Auto-Stop function.
  2. Ignition ON, verify the scan tool hood position parameter displays Open.
    • If the hood position does not display Open, refer to DTC P254F .
  3. Ignition OFF, remove the powertrain relay.
  4. Ignition ON, verify a test lamp illuminates between both of the following relay battery voltage circuit terminals and ground.
    • Terminal 85
    • Terminal 30
    • If the test lamp does not illuminate, repair the relay battery voltage circuit for a short to ground or an open/high resistance.
  5. Ignition OFF, connect a test lamp between the relay coil control circuit terminal 86 and B+.
  6. Cycle the ignition ON and OFF. The test lamp should turn ON when the ignition switch is cycled ON and OFF when the ignition switch is cycled OFF.
    • If the test lamp remains ON all the time, test the control circuit for a short to ground. If the circuit/connections test normal, replace the ECM.
    • If the test lamp remains OFF all the time, test the control circuit for a short to voltage or an open/high resistance. If circuit/connections test normal, replace the ECM.
    7. NOTE: The ignition voltage circuit is between the powertrain relay and the ECM. The ignition voltage is a feedback circuit.
  7. Connect a 20 A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay switch ignition voltage circuit terminal 87.
  8. Attempt to start the engine. The engine should start.
    • If the engine does not start, test the ignition voltage circuit between the powertrain relay and the ECM for a short to ground or for an open/high resistance. If the circuit/connections test normal, replace the ECM.
  9. If all circuits/connections test normal, test or replace the powertrain relay.
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