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DTC B2540

DTC B2540

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptor

DTC B2540 02

Rear Fog Lamps Control Circuit Short to Ground

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Rear Fog Lamps Control B2540 02 2 1 -
Tail Lamp Ground - 2 - -
1. Rear fog lamp always ON 2. Rear fog lamp always OFF


Circuit/System Description

The body control module (BCM) energizes the rear fog lamp by applying voltage to the rear fog lamp control circuit. When the rear fog lamp control circuit is energized the rear fog lamp is illuminated.

Conditions for Running the DTC

Rear fog lamp activated

Conditions for Setting the DTC

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

Action Taken When the DTC Sets

The rear fog lamp will be inoperative.

Conditions for Clearing the DTC


• The DTC will be current for as long as the fault is present.

• When the fault is no longer present, the DTC will be a history DTC.

• A history DTC will clear after 50 ignition cycles.


Reference Information

Schematic Reference

Fog Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, command the Rear Fog Lamp(s) Relay ON and OFF with a scan tool. The rear fog lamp should turn ON and OFF when changing between the commanded states.

Circuit/System Testing


1. Ignition OFF, disconnect the harness connector at the E5 fog lamp-rear.

2. Test for less than 30 Ω between the ground circuit terminal C and ground.

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

4. Connect a test lamp between the control circuit terminal A and ground.

5. Ignition ON, command the Rear Fog Lamp(s) Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

6. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM.

7. 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 K9 BCM.

8. If all circuits test normal, replace the E5 fog lamp-rear.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Tail Lamp Replacement

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