Rear Fog Lamps Malfunction
Rear Fog Lamps Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions 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 ground 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.
Reference Information
Schematic Reference
Fog Lights Schematics Fog Lights Schematics
Connector End View Reference
Component Connector End Views Folding Top 5 Bow Lowered Switch (CM7)
Description and Operation
Exterior Lighting Systems Description and Operation Exterior Lighting Systems
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Ignition ON, observe the scan tool Rear Fog Lamp Switch parameter while turning the rear fog lamp switch ON and OFF. The parameter should change between Active and Inactive.
• If the parameter does not change between the selected states, refer to Rear Fog Lamp Switch Malfunction.
2. Turn the rear fog lamps ON and OFF with the rear fog lamps switch. The rear fog lamps should turn ON and OFF when changing between the selected states.
• If the rear fog lamps do not change between the selected states, refer to Rear Fog Lamps Malfunction.
3. Command the Display Test ON and OFF with a scan tool. The rear fog lamps indicator should turn ON and OFF when changing between the commanded states.
• If the rear fog lamps indicator illuminates during the test, replace the BCM.
• If the rear fog lamps indicator does not illuminate during the test or remains illuminated at all times, replace the instrument cluster.
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 3 A 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 ON, verify that a test lamp does not illuminate between the control circuit terminal B6 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 relay switch B+ circuit terminal A4 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+ fuse is open, test the control circuit terminal B6 for a short to ground. If the circuit tests normal, test or replace the rear fog lamp relay.
4. Verify that a test lamp illuminates between the B+ circuit terminal B4 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 appropriate rear fog lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the rear fog lamp ground circuit terminal 1 and ground
• If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the rear fog lamp.
8. Connect a 10 A fused jumper wire between the B+ circuit terminal A4 and the control circuit terminal B6. Verify the rear fog lamps are illuminated.
• If the rear fog lamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the rear fog lamp.
9. Connect a test lamp between the B+ circuit terminal B4 and the control circuit terminal A6.
10. 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.
11. If all circuits test normal, replace the rear fog lamp relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)
* Turn Signal Multifunction Switch Replacement Turn Signal Multifunction Switch Replacement
* Control Module References Control Module References for BCM replacement, setup, and programming