Front Fog Lamps Malfunction

Front 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.

Circuit/System Description

With the ignition switch in the ON position, and the park lamps or low beam headlights ON, the fog lights will illuminate when the driver presses the fog lamp switch. The FRT FOG fuse in the underhood fuse block supplies battery positive voltage to the switch side of the FRT FOG relay. When the fog lamp switch is pressed, the body control module (BCM) fog lamp switch input is grounded. Ground is provided at G203. The BCM will then energize the FRT FOG relay control circuit. The current flow is now from the FRT FOG relay to both front fog lamps and to ground. Ground is provided at G101 and G102. The state of the fog lamps, either ON or OFF, will remain the same until the fog lamp switch is pressed again, or the ignition switch is cycled OFF and ON. Fog lamp operation will be cancelled whenever the park lamps, are turned OFF or the high beam headlights have been selected.

Circuit/System Verification

1. Ignition ON, place the headlamp switch in the PARK position.
2. Place the fog lamp switch in the OFF position.
3. Observer the fog lamps. The fog lamps should not be illuminated.

^ If the fog lamps are illuminated, refer to Fog Lamps Always On.

4. Command the fog lamps ON and OFF with a scan tool. The fog lamps should illuminate when commanded ON.

^ If the fog lamps do not illuminate, refer to Fog Lamps Inoperative From BCM.

5. Refer to Fog Lamps Inoperative From Switch.

Circuit/System Testing

Fog Lamps Always On
1. Ignition OFF, disconnect the FRT FOG relay.
2. Ignition ON, verify that the fog lamps are not illuminated.

^ If the fog lamps are illuminated, test the relay controlled output circuit for a short to voltage.
^ If all circuits test normal, replace the FRT FOG relay.

Fog Lamps Inoperative From BCM
1. Ignition OFF, disconnect the FRT FOG relay.
2. Ignition ON, verify that a test lamp illuminates between the relay switch B+ circuit and ground.

^ If the test lamp does not illuminate, replace the underhood fuse block.

3. Test the relay controlled output circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the FRT FOG relay.

Fog Lamps Inoperative From Switch
1. Verify the scan tool Front Fog Lamp Switch parameter is Inactive.

^ If not the specified value, test the fog lamp switch signal circuit for a short to ground. If the circuit tests normal, replace the fog lamp switch.

2. Disconnect the harness connector at the fog lamp switch.
3. Verify that a test lamp illuminates between the ground circuit terminal A and B+.

^ If the test lamp does not illuminate, test the ground circuit terminal A for a short to voltage or an open/high resistance.

4. Install a 3A fused jumper wire between the signal circuit terminal C and ground. Verify the scan tool Front Fog Lamp Switch parameter is Active.

^ If not the specified value, test the signal circuit terminal C for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Fog Lamp Switch Replacement
* Relay Replacement (Attached to Wire Harness)
* Underhood Electrical Center or Junction Block Replacement