For 1990-2009 cars

### 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.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC B2622 Dimming Display Pulse Width Modulation (PWM) Input Circuit Low

• | DTC B2623 Dimming Display Pulse Width Modulation (PWM) Input Circuit High

### Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

• | When the BCM receives an 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 an I/P controls illumination lamp request signal and the I/P lamps supply voltage circuit is shorted to voltage

### 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 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 .

### Test Description

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

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

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

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 Data Communication Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Clear the DTC B2622 or B2623 with the scan tool.
2. Turn the park lamps ON.
3. Adjust the instrument panel (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 4

Go to Step 3

3 | Test for one of the following conditions. Refer to Circuit Testing and Wiring Repairs .

• | A short to voltage or short to ground in the I/P lamps supply voltage circuit.

• | An open, high resistance or short to ground in the park lamp supply voltage circuit.

Did you find and correct the condition?

Go to Step 6

Go to Step 5

4 | 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 6 | --
5 | Replace the body control module (BCM). Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 6 | --
6 |

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