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Home >> Buick >> 2009 >> Allure CX >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System & Fuel System - 3.8L - DTC P0385 To DTC P2119 >> DTC P0685 >> Circuit/System Testing
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Circuit/System Testing

  1. Ignition OFF, disconnect the powertrain relay, which is P/train relay 40.
  2. Ignition ON, verify that a test lamp illuminates between the powertrain relay coil B+ terminal C5 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the battery positive cable to the underhood fuse block.
  3. Ignition OFF, verify that a test lamp does not illuminate between the powertrain relay coil B+ circuit terminal C5 and the control circuit terminal A6.
    • If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the PCM.
  4. Remove the test lamp.
  5. Ignition ON, verify with a scan tool that the powertrain relay EC Ignition Relay Circuit Status parameter is OK.
    • If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the PCM.
  6. Test the coil side of the powertrain relay terminals C5 and A6 for 65-110 ohms.
    • If not within the specified value, replace the relay.
  7. Ignition OFF, disconnect the PCM X1 connector.
  8. Test the powertrain relay control circuit X1-24 for an open/high resistance.
    • If the circuit tests normal, replace the PCM.
  9. Verify that a test lamp does not illuminate between the relay ignition 1 voltage circuit terminal A5 at the powertrain relay and ground.
    • If the test lamp illuminates, test the relay ignition 1 voltage circuit for a short to voltage between the powertrain relay and each component powered by the relay.
  10. Verify that a test lamp illuminates between the relay switch B+ terminal C6 and ground.
    • If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground, or an open/high resistance. If the circuits test normal, and the fuse for the ignition 1 voltage circuit is open, test the ignition 1 voltage circuit for a short to ground.
  11. Connect a 20A fused jumper wire between the relay switch B+ terminal C6 and the relay ignition 1 voltage circuit terminal A5.
  12. Ignition ON, engine OFF, probe the ignition voltage circuit for each component energized by the powertrain relay.
    • If the test lamp does not illuminate, test the ignition 1 voltage circuit for an open/high resistance.
  13. If all circuits test normal, replace the relay.
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