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 02
- Rear Fog Lamps Control Circuit Short to Ground

DTC B2540 04
- Rear Fog Lamps Control Circuit Open

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) responds to the rear fog lamp request by applying voltage to the rear fog lamp control circuit which illuminates the rear fog lamp.

Conditions for Running the DTC

* Battery voltage must be between 9-16 V.

* Rear fog lamp ON.

Conditions for Setting the DTC

DTC B2540 02

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

DTC B2540 04

The BCM detects an open/high resistance in the rear fog lamp control circuit.

Actions Taken When the DTC Sets

The rear fog lamp 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

Exterior Lights Schematics Exterior Lights Schematics

Connector End View Reference

Component Connector End Views Fuel Pump and Level Sensor Assembly

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 Testing

1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the E29R fog lamp - rear.

2. Test for less than 5 ohms between the ground circuit terminal B and ground.

• If 5 ohms or greater

1. Ignition OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 5 ohms

3. Connect a test lamp between the control circuit terminal A and ground, ignition ON.

4. Verify the test lamp turns ON and OFF when commanding the Rear Fog Lamp ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the X5 harness connector at the K9 body control module.

2. Test for infinite resistance between the control circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for less than 2 ohms in the control circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, replace the K9 body control module.

• If the test lamp is always ON

1. Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON.

2. Test for less than 1 V between the control circuit terminal and ground.

• If 1 V or greater, repair the short to voltage on the circuit.

• If less than 1 V, replace the K9 body control module.

• If the test lamp turns ON and OFF

5. Test or replace the E29R fog lamp - rear.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the repair.

* Stop and Tail Lamp Bulb Replacement Stop and Tail Lamp Bulb Replacement

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