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Front Fog Lamps Malfunction




Front 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 front fog lamp relay is supplied with battery voltage at all times via the FRT FOG LP fuse. The front fog lamp switch signal circuit is grounded momentarily by pressing the front fog lamp switch. The body control module (BCM) energizes the front fog lamp relay by applying voltage to the front fog lamp relay control circuit. When the front fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the FRT FOG LP fuse to the front fog lamp control circuit which illuminates the front fog lamps. The front fog lamp relay control circuit also controls the front fog lamp switch indicator.

Reference Information
Schematic Reference

Fog Lights Schematics (Fog Lights Schematics)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
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 (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON, observe the scan tool Front Fog Lamp Switch parameter while activating the fog lamp switch. The parameter should change between Active and Inactive.

• If the parameter does not change between the commanded states, refer to Fog Lamp Switch Malfunction.

2. Turn the fog lamps ON and OFF with the fog lamps switch. The fog lamps should turn ON and OFF as selected.

• If the fog lamps do not change between the selected states, refer to Fog Lamps Malfunction.

3. Turn the fog lamps ON and OFF with the fog lamps switch. The fog lamps switch indicator should illuminate ON and OFF as selected.

• If the fog lamps switch indicator does not change between the selected states, refer to Fog Lamp Switch Indicator Malfunction.

Circuit/System Testing

Fog Lamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the fog lamp switch.
2. Ignition OFF, exterior lamps OFF, test for less than 1 ohm between the ground circuit terminal A and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Front Fog Lamp Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal C 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 C and ground. 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 an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the front fog lamp switch.

Fog Lamps Malfunction
1. Ignition OFF, disconnect the front fog lamp relay.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohm between the ground circuit terminal 86 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. 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.

4. Verify that 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 front fog lamp relay.

5. Disconnect the harness connector at the appropriate front fog lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 1 ohm between the ground circuit terminal A and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the front fog lamp.
8. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the front fog lamps illuminate.

• If the front fog lamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the front fog lamp.

9. Connect a test lamp between the control circuit terminal 85 and ground.
10. Command the 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 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.

11. If all circuits test normal, test or replace the front fog lamp relay.

Fog Lamp Switch Indicator Malfunction
1. Ignition OFF, disconnect the harness connector at the fog lamp switch.
2. Ignition OFF, exterior lamps OFF, test for less than 1 ohm between the ground circuit terminal A and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the control circuit terminal B and ground.
4. Command the 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 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 an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the front fog lamp switch.

Repair Instructions

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

* Fog Lamp Switch Replacement (Service and Repair)
* Relay Replacement (Relay Replacement (Within an Electrical Center))
* Underhood Electrical Center or Junction Block Replacement (Underhood Electrical Center or Junction Block Replacement)
* Front Fog Lamp Replacement (Removal and Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming

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