GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The body control module (BCM) controls the illumination of the following lamps through pulse width modulation when the park lamps or the headlamps are ON:

    • The automatic transmission control position illumination lamp
    • The left glass window release switch illumination lamp
    • The electronic traction control switch illumination lamp
    • The door lock theft deterrent defeat switch illumination lamp
    • The heater A/C control switch illumination lamp
    • The instrument cluster illumination lamps
    • The headlamp switch illumination lamp
    • The radio switches illumination lamps
    • The driver information display switch illumination lamp
    • The heated seat switch illumination lamp
    • The door lock switches illumination lamps
    • The window switches illumination lamps
    • The steering wheel controls illumination lamps

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2628 Display Dimming Pulse Width Modulation Output Circuit High

Conditions for Running the DTC

Voltage supplied to the module is in the normal operating range, approximately 10-16 volts.

Conditions for Setting the DTC

    • The BCM detects a short to voltage in the instrument panel lamps supply voltage circuit. When the park lamps or the headlamps are ON, and the dimmer switch is in the OFF position.
    • The condition is present for more than 3 ms.

Action Taken When the DTC Sets

The BCM stores DTC B2628 in memory.

Conditions for Clearing the MIL/DTC

    • A current DTC B2628 clears if the BCM no longer detects a short to battery positive voltage in the instrument panel lamps supply voltage circuit of the illumination lamps.
    • A history DTC B2628 clears after 100 consecutive ignition cycles if the condition is no longer present.
    • The BCM receives the Clear Code command from the scan tool.

Diagnostic Aids

    • If the DTC B2628 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .
    • An intermittent short to voltage in the following conditions may cause an intermittent malfunction to occur:
       - The instrument panel lamps supply voltage circuit of the illumination lamps
       - The BCM

Step

Action

Yes

No

Schematic Reference: Interior Lights Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Do the instrument panel lamps turn ON with the headlamp switch in the PARK position?

Go to Diagnostic Aids

Go to Step 3

3

  1. Disconnect the body control module (BCM) connector C1.
  2. Connect a test lamp between the instrument panel lamps supply voltage circuit at the BCM connector and ground.

Do the test lamp illuminate?

Go to Step 4

Go to Step 5

4

Repair a short to battery positive voltage in the instrument panel lamps supply voltage circuit of the illumination lamps. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 6

--

5

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 6

--

6

  1. Use a 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?

System OK

Go to Step 3