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.

### 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) 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.

### 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 Verification

Ignition ON, observe the scan tool Dimming Potentiometer parameter while operating the dimmer switch from high to low. The voltage reading should change from high to low as the switch is rotated.

⇒ | If the reading does not change, refer to Dimmer Switch Malfunction.

⇒ | If the scan tool dimmer control operates normal, refer to Interior Backlighting Malfunction.

### Circuit/System Testing

#### Dimmer Switch Malfunction

1. Ignition OFF, disconnect the headlamp and panel dimmer switch connector.
2. Ignition OFF, verify that a test lamp illuminates between the low reference circuit terminal 3 and B+.

⇒ | If the test lamp does not illuminate, test the low reference circuit for an open/high resistance.

3. Ignition ON, verify that the scan tool dimming potentiometer parameter displays greater than 4 volts.

⇒ | If the parameter displays less than the specified value, test the switch signal circuit for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal 14 and the low reference circuit terminal 3. Verify the scan tool dimming potentiometer parameter displays less than 1 volt.

⇒ | If the parameter displays greater than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If the circuits test normal, test or replace the headlamp and panel dimmer switch.

#### Interior Backlighting Malfunction

1. Ignition OFF, disconnect the harness connector at the inoperative component.
2. Ignition OFF, verify that a test lamp illuminates between the appropriate component ground circuit terminal and B+.

• | HVAC control module X1 terminal 14

• | Hazard switch terminal B

• | Accessory switch terminal H

⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the appropriate component backlighting control circuit terminal and ground.

• | HVAC control module X1 terminal 13

• | Hazard switch terminal A

• | Accessory switch terminal G

4. Ignition ON and parklamps ON, operate the dimmer switch from high to low. The test lamp should illuminate bright to dim when rotating the dimmer switch.

⇒ | If the test lamp is always OFF, test the control circuit a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp is always bright, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the inoperative component.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Switch Replacement

• | Hazard Warning Switch Replacement

• | Accessory Switch Replacement

• | Control Module References for BCM, or HVAC module, replacement, setup, and programming