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Home >> Chevrolet >> 2006 >> Silverado 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1089 (Lighting Systems) >> Diagnostic Information and Procedures >> Rear Fog Lamps Malfunction >> Circuit/System Testing >> Rear Fog Lamps Malfunction

Rear Fog Lamps Malfunction

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 rear fog lamp relay.
  2. 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.
  3. 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 control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the rear fog lamp relay.
  4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  5. Disconnect the harness connector at the inoperative rear fog lamp.
  6. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms between the inoperative rear fog lamp ground circuit terminal B and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the inoperative rear fog lamp.
  8. Connect a 15A fused jumper wire between the B+ circuit terminal 30 and the relay controlled output circuit terminal 87. Verify the rear fog lamps are activated.
    • If the rear fog lamps do not activate, test the relay controlled output circuit terminal 87 for an open/high resistance. If the circuit tests normal, test or replace the inoperative rear fog lamp.
  9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  10. Command the rear fog lamps ON and OFF with the rear fog lamp switch. 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 ground. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or open/high resistance. If the circuit tests normal, replace the BCM.
  11. If all circuits test normal, test or replace the rear fog lamp relay.
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