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: Rear Fog Lamps Control CircuitDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Rear Fog Lamp Relay B+ | B2540 00 | B2540 00 | -- | -- |
Rear Fog Lamp Control | 1 | 1 | 1 | -- |
Rear Fog Lamp Switch Signal | 2 | 2 | -- | -- |
Rear Fog Lamp Relay Control | B2540 00 | B2540 00 | B2540 00 | -- |
Rear Fog Lamp Ground | -- | 1 | -- | -- |
Headlamp Switch Ground | -- | 2 | -- | -- |
1. Rear Fog Lamp Malfunction 2. Rear Fog Lamp Switch Malfunction | ||||
Circuit/System Description
The rear fog lamp relay is supplied with battery voltage at all times from the REAR FOG fuse located in the rear fuse block. The rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch. The body control module (BCM) energizes the rear fog lamp relay by applying ground to the rear fog lamp relay control circuit. When the rear fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the REAR FOG fuse to the rear fog lamp supply voltage circuit which illuminates the rear fog lamps.
Conditions for Running the DTC
The battery voltage must be between 9-16 volts.
Conditions for Setting the DTC
| • | When the BCM receives a rear fog lamp switch OFF command and the rear fog lamp relay control circuit is shorted to ground. |
| • | When the BCM receives a rear fog lamp switch ON command and the rear fog lamp relay control circuit is shorted to voltage or open. |
Action Taken When the DTC Sets
The rear fog lamps will be inoperative or always ON.
Conditions for Clearing the DTC
| • | This DTC will clear on current status after the condition for setting the fault is corrected. |
| • | A history DTC will clear after 100 consecutive ignition cycles without a fault present. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
- Ignition OFF, disconnect the rear fog lamp relay.
- Ignition ON, verify that a test lamp does not illuminate between the rear fog lamp control circuit terminal 87 and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
- Disconnect the harness connector at the inoperative rear fog lamp.
- Test for less than 5.0 ohms between the rear fog lamp ground circuit terminal E and ground.
- Ignition OFF, connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87..
- Connect a test lamp between the control circuit terminal C and ground. Verify the test lamp illuminates.
- If all circuits test normal, replace the rear fog lamp relay.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit terminal for a short to ground or an open/high resistance. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit terminal for a short to ground or an open/high resistance. |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. |
| ⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for BCM replacement, programming, and setup.
