B2540

DTC B2540

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.

DTC Descriptors

DTC B2540 00

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Rear Fog Lamps Control Circuit

Diagnostic Fault Information






Circuit/System Description

The body control module (BCM) controls the rear fog lamps based on inputs from the headlamp switch. When the rear fog lamp switch is pressed, a ground path is provided on the rear fog lamp switch signal circuit to the BCM, indicating the rear fog lamps ON command. In response to this signal, the BCM grounds the rear fog lamp relay control circuit energizing the Rear Fog Lamp Relay. With the rear fog lamp relay energized, battery voltage is applied through the RR FOG Fuse and the rear fog lamp control circuits illuminating the rear fog lamps.

Conditions for Running the DTC

* Battery voltage must be between 9-16 V.

* Rear fog lamps ON.

Conditions for Setting the DTC

The BCM detects a short to ground in the rear fog lamp switch signal circuit.

Action Taken When the DTC Sets

The rear fog lamps will not operate when the park lamps are ON and the rear fog lamp switch is active.

Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.

* A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Reference Information

Schematic Reference

Fog Lights Schematics Fog Lights Schematics

Connector End View Reference

Component Connector End Views A/C Compressor Clutch

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 Testing

1. Ignition OFF, disconnect the harness connector at the headlamp switch.

2. Verify that a test lamp illuminates between B+ and the ground circuit terminal 8.

• 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 10 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 10 and the ground circuit terminal 8. 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.

Repair Instructions

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

* Headlamp Switch Replacement Service and Repair

* Control Module References Programming and Relearning for BCM replacement, programming and setup