GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The body control module (BCM) receives a variable voltage signal from the instrument panel (I/P) dimmer switch requesting to illuminate the dimming lamps to a desired intensity. When this occurs, the BCM directly sends a pulse width modulated (PWM) voltage based on the I/P dimmer switch position on the LED dimming signal circuit, instrument panel lamps dimming control circuit, and the backlight lamps control circuit.

Voltage for the LED dimming signal circuit, instrument panel lamps dimming control circuit, and the backlight lamps control circuit is from the TBC 3 fuse 16 in the underhood fuse block directly through the BCM to these circuits.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2625 Display Dimming Pulse Width Modulation (PWM) Output Circuit

Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

    • The backlight lamps control circuit is shorted to ground.
    • The I/P lamps dimming control circuit is shorted to ground.
    • The LED dimming signal circuit is shorted to ground.
    • There is a loss of the underhood fuse block TBC 3 battery supply voltage to the BCM for 1 second.

Action Taken When the DTC Sets

The dimming 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 DTCs can be cleared using a scan tool.

Diagnostic Aids

    • 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.
    • A short to ground in the following circuits will cause the TBC 3 fuse to open.
       - The backlight lamps control.
       - The instrument panel lamps dimming control.
       - The LED dimming signal.
       - Battery positive voltage from the underhood fuse block TBC 3 fuse.
    • An open in the TBC 3 fuse will cause the BCM to set the following DTC:
       - B0951
       - B2610
       - B2625

Test Description

The number below refers to the step number on the diagnostic table.

  1. After replacement of the BCM, you must calibrate the new module for proper operation.

Step

Action

Yes

No

Schematic Reference: Interior Lights Dimming Schematics

Connector End View Reference: Lighting Systems Connector End Views or Computer/Integrating Systems Connector End Views in Computer/Integrating Systems

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Test the following circuits for a short to ground:

    • Backlight lamps control
    • Instrument panel (I/P) lamps dimming control
    • LED dimming signal
    • Battery positive voltage circuit of the body control module (BCM) from the TBC 3 fuse

Did you find and correct the condition?

Go to Step 5

Go to Step 3

3

Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 5

Go to Step 4

4

Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 5

--

5

  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