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Stop Lamps Malfunction - European

WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the X4 harness connector at the BCM.
  2. Ignition ON, verify that a test lamp illuminates between the BCM 5 fuse voltage supply circuit terminal 1 and ground.
    • If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the BCM 6 fuse voltage supply circuit terminal 3 and ground.
    • If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance.
  4. Ignition OFF, reconnect the X4 harness connector at the BCM.
  5. Ignition OFF, disconnect the stop lamp relay.
  6. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal 85 and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
    • If the test lamp illuminates, test the control circuit for a short to voltage.
  8. Verify that a test lamp illuminates between the B+ circuit terminal 30 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 and the B+ circuit fuse is open, test the relay control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the stop lamp relay.
  9. Connect a test lamp between the control circuit terminal 86 and the ground circuit terminal 85.
  10. Ignition ON, command the stop lamps ON and OFF by applying the brake pedal. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  11. Disconnect the harness connector at the inoperative stop lamp.
  12. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal H and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  13. Connect a test lamp between the control circuit terminal B and the ground circuit terminal H.
  14. Ignition ON, command the stop lamps ON and OFF by commanding the appropriate rear turn signal parameter 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 control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  15. If all circuits test normal, replace the inoperative tail lamp assembly.
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