The RR FOG LMP relay is supplied with B+ at all times from the RR FOG fuse located in the underhood fuse block. The rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch. The body control module (BCM) energizes the RR FOG LMP relay by applying ground to the rear fog lamp relay control circuit. When the rear fog lamp relay is energized, the relay switch contacts close and B+ is applied through the RR FOG fuse to the rear fog lamp supply voltage circuit which illuminates the rear fog lamps.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool rear fog lamp switch parameter while activating the rear fog lamp switch. The reading should toggle between ACTIVE and INACTIVE.

Rear Fog Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify a test lamp illuminates between B+ and the ground circuit terminal 3.

⇒	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 13 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 13 and the ground circuit terminal 3. 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 BCM.

5. If all circuits test normal, test or replace the headlamp switch.

Rear Fog Lamps Malfunction

1. Ignition OFF, disconnect the RR FOG LMP relay.
2. Ignition ON, verify a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify 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. If the circuit tests normal, and the B+ circuit fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the RR FOG LMP relay.

4. Verify 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 inoperative rear fog lamp.
6. Ignition OFF, 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.

7. Connect the harness connector at the inoperative rear fog lamp.
8. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the rear fog lamps are activated.

⇒	If the rear fog lamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the inoperative rear fog lamp.

9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. Command the rear fog lamps ON and OFF with the Rear Fog Lamp Switch. 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 open/high resistance. If the circuit tests normal, replace the BCM.

11. If all circuits test normal, test or replace the Rear Fog Lamp Relay.

Rear Fog Lamp Indicator Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition ON, headlamps ON, connect a test lamp between the indicator control circuit terminal 13 and ground. The test lamp should not illuminate.

⇒	If the test lamp does not illuminate, test the indicator control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

3. Command the rear fog lamps ON with a scan tool. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the indicator control circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the BCM.

4. If all the circuits test normal, replace the headlamp switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.