For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC B2622 00: Dimming Display Pulse Width Modulation (PWM) Input Circuit Low
DTC B2623 00: Dimming Display Pulse Width Modulation (PWM) Input Circuit High

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Body Control Module B+ | B2622 00 | B2622 00 | B2622 00 | --
I/P Lamps Dimmer Switch Signal | B2622 00 | 2 | B2623 00 | --
Accessory Switch Control | B2622 00 | 1 | B2623 00 | --
Hazard Switch Control | B2622 00 | 1 | B2623 00 | --
HVAC Control Module Control | B2622 00 | 1 | B2623 00 | --
I/P DImmer Control | B2624 00 | B2624 00 | B2624 00 | --
Accessory Switch Ground | -- | 1 | -- | --
Hazard Switch Ground | -- | 1 | -- | --
HVAC Control Module Ground | -- | 1 | -- | --
Headlamp and Panel DImmer Switch Low Reference | 2 | 2 | 2 | --

1. Interior Backlighting Malfunction
2. Headlamp and Panel DImmer Switch Malfunction

### Circuit/System Description

The instrument panel (I/P) lamp dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The I/P dimmer switch provides a voltage signal that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The body control module (BCM) provides a low reference signal and a B+ voltage reference to the I/P dimmer switch. When the I/P dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the I/P dimmer switch through the I/P dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies the dimmed voltage to the I/P lamps supply voltage circuit and the interior backlighting components dim to the requested level.

### Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

#### B2622 00

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

#### B2623 00

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 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.

### Reference Information

#### Schematic Reference

Interior Lights Dimming Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Interior Lighting Systems Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the BCM connector X2.
2. Ignition ON, verify that the following components backlighting is not illuminated.

• | Hazard switch

• | HVAC control module terminal

• | Headlamp switch

⇒ | If any of the listed components backlighting is illuminated, test the associated control circuit for a short to voltage.

3. Connect a fused jumper wire from B+ to the following terminals and verify associated backlighting operation.

• | Hazard switch A28

• | HVAC control module terminal A29

• | Headlamp switch A36

⇒ | If the jumper fuse opens while connected to any of the listed terminals, test the associated control circuit for a short to ground.

4. If all circuits test normal, replace the BCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM replacement, programming, and setup.