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 body control module (BCM) controls the fog lamps based on inputs from the fog lamp switch. When the fog lamp switch is pressed, a ground path is provided on the front fog lamp switch signal circuit to the BCM, indicating the front fog lamps ON command. In response to this signal, the BCM grounds the fog lamp relay control circuit energizing the FOG LAMP PCB Relay. With the fog lamp relay energized, battery voltage is applied through the FOG LAMPS Fuse and the fog lamp supply voltage circuits illuminating the front fog lamps.
When a fog lamp request is seen by the BCM, a serial data message is sent to the instrument panel cluster (IPC) requesting the fog lamp indicator be illuminated.
Circuit/System Verification
1. Observe the scan tool Rear Fog Lamps Switch parameter while pressing and releasing the fog lamp switch. The parameter should change between Active and Inactive.
• If the parameter does not change between the specified values, refer to Fog Lamp Switch Circuit Test.
2. With a test lamp connected to ground, probe each of the test points on the FOG Fuse while commanding the Fog Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF at one or both of the fuse test points when changing between commanded states.
• If the test lamp is always OFF, or remains always ON, refer to Fog Lamp PCB Relay Circuit Test.
• If the test lamp turns ON and OFF, refer to Fog Lamps Circuit Test.
3. With the fog lamps ON, verify the fog lamp indicator is illuminated on the IPC.
• If the indicator does not illuminate, refer to Rear Fog Lamp Indicator Test.
Circuit/System Testing
Fog Lamp Switch Circuit Test
1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 8 and B+.
• If the test lamp does not illuminate, 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 10 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 10 and the ground circuit terminal 8. Verify the scan tool Front Fog Lamp Switch parameter is Active.
• If not the specified value, test the signal circuit for a short to voltage or and 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 PCB Relay Circuit Test
1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal 40 and B+.
3. Ignition ON, command the Rear Fog Lamps 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 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.
4. If all circuits test normal, replace the underhood fuse block.
Fog Lamps Circuit Test
1. Ignition OFF, disconnect the harness connector at the inoperative fog lamp.
2. Test for less than 5.0 ohms 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 supply voltage circuit terminal A and ground.
4. Ignition ON, command the Rear Fog Lamps 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 supply voltage circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.
• If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
5. If all circuits test normal, test or replace the inoperative fog lamp.
Front Fog Lamp Indicator Test
Ignition ON, with a scan tool perform the display test for the instrument panel cluster (IPC) and observe the rear fog lamp indicator.
If the rear fog lamp indicator illuminates during the test, replace the BCM.
If the front fog lamp indicator does not illuminate or remains illuminated at all times, replace the IPC.
Component Testing
Headlamp Switch
1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for infinite resistance between the signal circuit terminal 10 and the ground circuit terminal 8 with the switch in the open position.
• If not the specified value, replace the headlamp switch.
3. Test for less than 2.0 ohms between the signal circuit terminal 10 and the ground circuit terminal 8 with the switch in the closed position.
• If greater than the specified range, replace the headlamp switch.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Rear Fog Lamp Switch Replacement
* Rear Fog Lamp Replacement
* Rear Fog Lamp Bulb Replacement