Rear Fog Lamps Malfunction
Rear Fog Lamps Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch. The body control module (BCM) energizes the rear fog lamp relay by applying voltage to the rear fog lamp relay control circuit. When the rear fog lamp relay is energized, battery voltage is applied via the REAR FOG/ALDL TOP SW fuse to the rear fog lamp supply voltage circuit which illuminates the rear fog lamps. The BCM sends a message via class 2 serial data to the instrument panel cluster (IPC) to enable the rear fog lamp indicator.
Reference Information
Schematic Reference
Fog Lights Schematics (Fog Lights Schematics)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning)
Circuit/System Verification
Ignition ON, observe the scan tool rear fog lamp switch parameter while pressing and releasing the rear fog lamp switch. The reading should toggle between ACTIVE and INACTIVE.
If the reading does not change between the commanded states, refer to Rear Fog Lamp Switch Malfunction.
Circuit/System Testing
Rear Fog Lamp Switch Malfunction
1. Ignition OFF, disconnect the X1 harness connector at the turn signal multifunction switch.
2. Ignition OFF, verify that 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 2 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 2 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 terminal 2 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 turn signal/multifunction switch.
Rear Fog Lamps Malfunction
1. Ignition OFF, disconnect the rear fog lamp relay.
2. Ignition OFF, test for less than 5 ohms of resistance between the ground circuit terminal B1 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Connect a test lamp between the front fog lamp relay control circuit terminal B2 and the ground circuit terminal B1.
4. Command the front 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 voltage. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the BCM.
5. Verify that a test lamp illuminates between the relay switch B+ circuit terminal B3 and ground.
• If the test lamp does not illuminate, test the relay switch B+ circuit terminal B3 for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit terminal B5 for a short to ground.
6. Disconnect the harness connector at the Inoperative rear fog lamp.
7. Ignition OFF, exterior lamps OFF, test for less than 5 ohms of resistance between the inoperative rear fog lamp ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
8. Connect the harness connector at the inoperative rear fog lamp.
9. Connect a 10A fused jumper wire between the B+ circuit terminal B3 and the relay controlled output circuit terminal B5. Verify the rear fog lamps are activated.
• If the rear fog lamps do not activate, test the relay controlled output circuit terminal B5 for an open/high resistance. If the circuit tests normal, test or replace the inoperative rear fog lamp.
10. If all circuits test normal, test or replace the rear fog lamp relay.
Rear Fog Lamp Indicator Malfunction
1. Ignition ON, with a scan tool perform the display test for the IPC and observe the rear fog lamp indicator.
• If the rear fog lamp indicator illuminates during the test, replace the BCM.
• If the rear fog lamp indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Turn Signal Multifunction Switch Replacement (Turn Signal Multifunction Switch Replacement)
* Control Module References (Programming and Relearning)for BCM or IPC replacement, setup, and programming