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 rear fog lamp (Export) is located in the left tail lamp assembly. The rear fog lamp has a dedicated relay and both the relay control and current flow operate the same as the front fog lamps. The RR FOG fuse supplies voltage to the lamp and G 401 supplies ground.
Circuit/System Verification
Ignition ON, headlamps ON, verify the scan tool rear fog lamp switch parameter changes between on and off when turning the rear fog lamp switch on and off.
If the scan tool parameter does not change between on and off, refer to the fog lamp switch circuit test.
If the switch operates normal but the rear fog lamps do not turn on and off, refer to the fog lamp control circuit test.
Circuit/System Testing
Fog Lamp Switch Circuit Test
1. Ignition OFF, disconnect the harness connectors at the headlamp switch.
2. Test for less than 1 ohm between the ground circuit terminal X1 C 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 off.
^ If not the specified value, test the signal circuit terminal X2 B for a short to ground. If the circuit tests normal, replace the BCM.
4. Install a 3A fused jumper wire between the signal circuit terminal X2 B and the ground circuit terminal X1 C. Verify the scan tool rear fog lamp switch parameter is on.
^ 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 BCM.
5. If all circuits test normal, test or replace the headlamp switch.
Fog Lamp Control Circuit Test
1. Ignition OFF, disconnect the rear fog lamp relay.
2. Ignition ON, verify that a test lamp does not illuminate between the rear fog lamp 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.
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 affected fog lamp.
6. Test for less than 1 ohm between the fog lamp ground circuit terminal E and ground.
^ If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the fog lamp.
8. Connect a 15A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the fog lamps are on.
^ If the fog lamps are not on, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the affected fog lamp.
9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. Headlamps on turn the rear fog lamps on and off. 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 an open/high resistance. If the circuit tests normal, replace the BCM.
11. If all circuits test normal, test or replace the RR FOG LP relay.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Headlamp Switch Replacement