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Circuit/System Testing

WARNING: This page is about a different car, the 2007 Buick Lucerne. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition ON, automatic head lights OFF, verify the scan tool LO BEAM relay command parameter displays ON with the head lamp switch in the ON position.
    • If the scan tool displays OFF, test the head lamp switch head lamps ON signal circuit terminal 1 and head lamp switch ground circuit terminal 8 for a short to voltage or an open/high resistance. If the circuits test normal, replace the head light switch.
  2. Ignition OFF, disconnect the LOW BEAM relay.
  3. Verify that a test lamp illuminates between the B+ circuit on the coil side and switch side of the relay terminals when connected to 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 and the B+ circuit fuse is open, test the left and right low beam supply voltage circuits for a short to ground. If the circuits test normal replace the appropriate head lamp assembly.
  4. Disconnect the harness connector at an inoperative head lamp assembly.
  5. Test for less than 1.0 ohm of resistance between the inoperative head lamp ground circuit terminal F and ground.
    • If greater than 1.0 ohm, test the ground circuit for an open/high resistance.
  6. Connect the harness connector at the head lamp.
  7. Connect a 30-amp fused jumper wire between the B+ circuit terminal and the appropriate head lamp supply voltage circuit terminal of the low beam head lamp relay. Verify the head lamps illuminate.
    • If the head lamps do not illuminate, test the left and right head lamp supply voltage circuits for an open/high resistance. If the circuits test normal, replace the inoperative head lamp assembly.
  8. Connect a test lamp between the B+ circuit terminal of the relay and the Low Beam relay control circuit terminal.
  9. Command the LO BEAM 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 OFF, test the low beam relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the Body Control Module.
  10. If all circuits test normal, replace the LO BEAM relay.
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