Rear Fog Lamps Malfunction

Rear Fog Lamps Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* 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.

Circuit/System Verification

1. Ignition ON, observe the scan tool Rear Fog Lamp Switch parameter while pressing and releasing the rear fog lamp switch. The reading should change between Active and Inactive.

^ If not the specified value, refer to the rear fog lamp switch circuit test.

2. Ignition ON, command the Rear Fog Lamps ON and OFF with a scan tool. Verify the front fog lamp turns on and off.

^ If the front fog lamp is always on or always off, refer to the fog lamp control circuit test.

Circuit/System Testing

Fog Lamp Switch Circuit Test
1. Ignition OFF, disconnect the harness connector at the headlamp 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 3A 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 switch.

Fog Lamp Control Circuit Test
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 after completing the diagnostic procedure. Verification Tests

* Rear Fog Lamp Bulb Replacement (Cadillac Export)
* Headlamp Switch Replacement (Cadillac) Headlamp Switch Replacement (Except Cadillac)