GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Yukon XL - 4WD 🢒 DTC 🢒 DTC B2537

Circuit Description

The body control module (BCM) monitors the rear fog lamp switch signal circuit in order to determine when the rear fog lamp relay is to be energized. When the BCM senses that the rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch, the BCM energizes the rear fog lamp relay by grounding the rear fog lamp relay control circuit.

Conditions for Running the DTC

The battery voltage must be between 9.0-16.0 volts.

Conditions for Setting the DTC

When the rear fog lamp switch signal circuit is shorted to ground for approximately 15 seconds.

Action Taken When the DTC Sets

The rear fog lamps will not operate.

Conditions for Clearing the MIL/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.
    • History and current DTC(s) can be cleared using a scan tool.

Diagnostic Aids
    • Test the rear fog lamp switch for sticking in the ON position.
    • Perform a visual inspection for loose or poor connections at all related components. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Step

Action

Yes

No

Schematic Reference: Fog Lights Schematics

Connector End View Reference: Lighting Systems Connector End Views or Body Control System Connector End Views in Body Control System.

1

Did you perform the Lighting Systems Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the rear fog lamp switch parameter in the Body Control Module (BCM) data list.

Does the scan tool display INACTIVE?

Go to Step 3

Go to Step 4

3
  1. Activate the front fog lamp switch.
  2. Activate the rear fog lamp switch.
  3. With the scan tool, observe the rear fog lamp switch data parameter.

Does the rear fog lamp switch data parameter change state?

Go to Diagnostic Aids

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the rear fog lamp switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the rear fog lamp switch data parameter.

Does the scan tool display INACTIVE?

Go to Step 7

Go to Step 5

5

Test the signal circuit of the rear fog lamp switch for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 6

6

Inspect for poor connections at the harness connector of the Body Control Module (BCM). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 8

7

Inspect for poor connections at the harness connector of the rear fog lamp switch. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

8

Important: Perform the setup procedure for the BCM.

Replace the body control module (BCM). Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 10

--

9

Replace the rear fog lamp switch. Refer to Rear Fog Lamp Switch Replacement .

Did you complete the replacement?

Go to Step 10

--

10
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK