GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Canyon Pickup - 4WD 🢒 DTC 🢒 DTC B2622 or B2623

Circuit Description

The body control module (BCM) receives a variable voltage signal from the instrument panel (I/P) dimmer switch requesting to illuminate the I/P controls illumination lamps to a desired intensity. When this occurs, the BCM directly sends a variable voltage based on the I/P dimmer switch position through the I/P lamps supply voltage circuit to the I/P controls illumination lamps.

Conditions for Running the DTC

The battery voltage must be between 9.0-16.0 volts.

Conditions for Setting the DTC
    • When the BCM receives a I/P controls illumination lamp request signal and the I/P lamps supply voltage circuit is shorted to ground.
    • When the BCM is not receiving a I/P controls illumination lamp request signal and the I/P lamps supply voltage circuit is shorted to voltage.
    • When the BCM receives a I/P controls illumination lamp request signal and the park lamp relay control circuit is open.

Action Taken When the DTC Sets

The I/P controls illumination lamps will not operate or are always on.

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

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.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step test determines by process of elimination which, if any, dimmable component is causing the DTC to set.

    2.

  2. This step test determines if the problem exists in the wiring or the BCM.

    3.

  3. 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 Body Control System Connector End Views in Body Control System

1

Did you perform the Lighting System Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

Do the park lamps operate normally?

Go to Step 3

Go to Step 5

3

  1. Clear the DTC B2622 or B2623 with the scan tool.
  2. Turn the park lamps ON.
  3. Adjust the I/P dimmer switch to a mid range dimming position.
  4. Disconnect each dimmable component from the instrument panel lamps dimming control circuit, one at a time, while monitoring the scan tool current codes.

Does either DTC not reset after a particular dimmable component was disconnected?

Go to Step 6

Go to Step 4

4

Test the instrument panel lamps supply voltage circuit for an short to voltage or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 7

5

Repair the open or high resistance in the park lamp relay control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 8

--

6

Replace the dimmable component associated with when the code did not reset. Refer to the proper replacement procedure for that particular component.

Did you complete the repair?

Go to Step 8

--

7

Important: Perform the setup procedure for the body control module (BCM).

Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 8

--

8
  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