Rear Fog Lamps Malfunction
Rear Fog Lamps Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The auxiliary body control module (XBCM) controls and supplies battery positive voltage to both the rear fog lamp and trailer rear fog lamp circuits.
Reference Information
Schematic Reference
Fog Lights Schematics (Fog Lights Schematics)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Ignition ON, observe the scan tool Rear Fog Lamp Switch parameter while turning the rear fog lamp switch ON and OFF. The parameter should change between Active and Inactive.
• If the parameter does not change between the selected states, refer to Rear Fog Lamp Switch Malfunction.
2. Turn the rear fog lamps ON and OFF with the front fog lamps switch. The rear fog lamps should turn ON and OFF as selected.
• If the rear fog lamps do not change between the selected states, refer to Rear Fog Lamps Malfunction.
3. Command the Lamp Test ON and OFF with a scan tool. The rear fog lamps indicator should turn ON and OFF when changing between the commanded states.
• If the rear fog lamps indicator illuminates during the test, replace the BCM.
• If the rear fog lamps indicator does not illuminate during the test or remains illuminated at all times, replace the instrument cluster.
Circuit/System Testing
Rear Fog Lamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
2. Test for less than 1 ohm between the ground circuit terminal 8 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Rear Fog Lamp Switch parameter is Inactive.
• If not the specified value, test the signal circuit terminal 6 for a short to ground. If the circuit tests normal, replace the XBCM.
4. Install a 3 A fused jumper wire between the signal circuit terminal 6 and the ground circuit terminal 8. Verify the scan tool Rear Fog Lamp Switch parameter is Active.
• If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the XBCM.
5. If all circuits test normal, test or replace the headlamp and panel dimmer switch.
Rear Fog Lamps Malfunction
1. Ignition OFF, disconnect the harness connector at the rear fog lamp.
2. Test for less than 1 ohm between the ground circuit terminal B and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Connect a test lamp between the control circuit terminal A and the ground circuit terminal B.
4. Command the Rear Fog Lamp 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 XBCM.
• 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 XBCM.
5. If all circuits test normal, test or replace the rear fog lamp.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Headlamp Switch Replacement (Cadillac) (Headlamp Switch Replacement (Cadillac)) Headlamp Switch Replacement (Except Cadillac) (Headlamp Switch Replacement (Except Cadillac))
* Control Module References (Programming and Relearning) for XBCM replacement, programming, and setup