For 1990-2009 cars

### Diagnostic Instructions

1. Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
2. Review Strategy Based Diagnosis for an overview of the diagnostic approach.
3. Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC B2540 01: Rear Fog Lamps Control Circuit Short to Battery
DTC B2540 02: Rear Fog Lamps Control Circuit Short to Ground
DTC B2540 04: Rear Fog Lamps Control Circuit Open

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Rear Fog Lamps Control | B2540 02 | B2540 04 | B2540 01 | --

### 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

#### B2540 01

The BCM detects a short to voltage on the control circuit.

#### B2540 02

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

#### B2540 04

The BCM detects an open control circuit.

### Action Taken When the DTC Sets

The rear fog lamp are inoperative.

### Conditions for Clearing the DTC

The condition for setting the DTC is no longer present.

### 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, perform the Rear Fog Lamps Relay Command test. The rear fog lamp should be ON/OFF when changing between the commanded states.

### Circuit/System Testing

1. Ignition OFF, disconnect the appropriate harness connector at the tail lamp listed below:

• | E29LR Fog Lamp - Left Rear

• | E29RR Fog Lamp - Right Rear

2. Test for less than 5 Ω between the appropriate ground circuit harness connector terminal listed below and ground:

• | E29LR Fog Lamp - Left Rear harness connector terminal 2

• | E29RR Fog Lamp - Right Rear harness connector terminal 2

⇒ | If greater than the specified value, test the appropriate ground circuit for an open/high resistance.

3. Connect a test lamp between the appropriate control circuit harness connector terminal listed below and ground :

• | E29LR Fog Lamp - Left Rear harness connector terminal 1

• | E29RR Fog Lamp - Right Rear harness connector terminal 1

4. Ignition ON, perform the Rear Fog Lamps Relay Command test. The test lamp should be ON/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 K9 Body Control Module (BCM).

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the K9 Body Control Module (BCM).

5. If all circuits test normal, test or replace the appropriate tail lamp.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Tail Lamp Replacement

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