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 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/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 lamps control circuit which illuminates 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
DTC B2540 01
The BCM detects a short to voltage in the rear fog lamps control circuit for 5 seconds or greater.
DTC B2540 02
The BCM detects a short to ground in the rear fog lamps control circuit.
DTC B2540 04
The BCM detects an open/high resistance in the rear fog lamps control circuit.
Actions 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 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 appropriate component listed below.
* E29LR fog lamp - left rear with CZ2
* E42LR tail lamp assembly - left without CZ2
* E42RR tail lamp assembly - right without CZ2
2. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground.
* E29LR fog lamp - left rear terminal 2
* E42LR tail lamp assembly - left terminal 1
* E42RR tail lamp assembly - right terminal 1
• 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 appropriate control circuit terminal listed below and ground, ignition ON.
* E29LR fog lamp - left rear terminal 1
* E42LR tail lamp assembly - left terminal 5
* E42RR tail lamp assembly - right terminal 7
4. Verify the test lamp turns ON and OFF when commanding the Rear Fog Lamps 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 appropriate E29 fog lamp - rear.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Tail Lamp Bulb Replacement Service and Repair
* Tail Lamp Replacement - Outboard Tail Lamp Replacement - Outboard
* Control Module References Control Module References for BCM replacement, programming, and setup