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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls And Fuel - 3.8L - DTC P0350 To DTC P0607 >> DTC P0412 or P0418 >> Circuit/System Testing
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Circuit/System Testing

  1. Ignition OFF, disconnect the affected relay.
  2. Ignition ON, connect a test lamp between the positive terminal at the battery and the relay control circuit terminal.
  3. Command the relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the relay control circuit for a short to ground. If the circuit tests normal, replace the PCM.
    • If the test lamp is always OFF, test the relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.
  4. Connect an appropriately fused jumper wire between the positive voltage terminal at the battery and the load voltage supply circuit terminal and verify load activation.
    • If the load does not activate, test the load voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the load.
  5. Ignition ON, connect an appropriately fused jumper wire between the relay switch voltage supply circuit terminal and the load voltage supply circuit terminal and verify load activation.
    • If the load does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all components connected to the fuse and replace as necessary.
  6. Ignition ON, verify that a test lamp illuminates between the relay coil voltage supply circuit terminal and ground.
    • If the test lamp does not illuminate, test the affected relay coil voltage supply circuit for a short to ground or an open/high resistance.
  7. If all circuits and the PCM test normal, test or replace the affected relay.
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