B2740
DTC B2740
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 Descriptor
DTC B2740 00
- Front Fog Lamp Switch Circuit Malfunction
Diagnostic Fault Information
Circuit/System Description
The front fog lamp switch is contained within the headlamp switch assembly. The body control module (BCM) provides a low reference signal and a B+ voltage reference to the front fog lamp switch. The front fog lamp switch shares the B+ reference and signal circuit with the I/P dimmer switch. Both switches utilize an internal resistor ladder that will vary the voltage depending on what switch function is activated. When the front fog lamp switch is activated, voltage from the B+ reference circuit is pulled down through the fog lamp resistor providing a voltage signal to the BCM via the I/P dimmer/front fog lamp switch signal circuit. The BCM interprets the signal as a front fog lamp request and energizes the front fog lamp relay by applying ground to the front fog lamp relay control circuit. When the front fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the F48UA fuse to the front fog lamp control circuit which illuminates the front fog lamps.
Conditions for Running the DTC
* Battery voltage must be between 9-16 V.
* Front fog lamps ON.
Conditions for Setting the DTC
The BCM detects a constant voltage on the I/P dimmer/front fog lamp switch signal circuit.
Actions Taken When the DTC Sets
The front fog lamps will not operate.
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 Sunshade - Left (D61)
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 and all vehicle systems OFF, disconnect the harness connector at the S30 headlamp switch, ignition ON.
2. Test for B+ between the B+ circuit terminal 1 and ground.
• If less than B+
1. Ignition OFF, disconnect the X3 harness connector at the K9 body control module.
2. Test for infinite resistance between the B+ 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 B+ 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 B+
3. Verify the scan tool LED Backlight Dimming Command parameter is greater than 40%.
• If 40% or less
1. Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON.
2. Test for less than 1 V between the signal circuit terminal 12 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 greater than 40%
4. Install a 3 A fused jumper wire between the signal circuit terminal 12 and the B+ circuit terminal 1.
5. Verify the scan tool LED Backlight Dimming Command parameter is less than 30%.
• If 30% or greater
1. Ignition OFF, disconnect the X1 harness connector at the K9 body control module.
2. Test for infinite resistance between the signal 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 signal 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 less than 30%
6. Test or replace the S30 headlamp switch.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Headlamp Switch Replacement Service and Repair
* Control Module References Control Module References for BCM replacement, programming, and setup