For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle

• | Review Strategy Based Diagnosis

• | Diagnostic Procedure Instructions

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Dimming 12-Volt Reference | B257B 03 | B257B 03 | -- | --
Instrument Panel Lamps Dimmer Switch Signal | B257B 03 | B257B 03 | B257B 07 | --
Interior Backlighting Control | B255D 02, B2610 02, B2625 02, B2652 02 | 2, | 1 | --
Interior Backlighting Ground | -- | 2 | -- | --
1. Interior backlighting at full Intensity and cannot be dimmed 2. Interior backlighting do not Illuminate

### Circuit/System Description

The body control module (BCM) supplies a voltage reference through the through the instrument panel cluster dimming voltage reference circuit to the instrument panel cluster lamps dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the dimmer switch rheostat and the instrument panel cluster lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the instrument panel , the backlight lamp control circuit, and the LED dimming control circuit illuminating the LEDs and instrument panel cluster lamps.

### 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

### Circuit/System Verification

1. Ignition ON, observe the scan tool Indicator Backlight Command parameter while operating the dimmer switch from high to low. The reading should change from a high percent to a low percent as the switch is rotated.

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

2. Command the Incandescent Dimming test to change intensity with the scan tool. The appropriate incandescent lighting items should change in intensity.

⇒ | If any incandescent lighting items do not change in intensity, refer to Interior Backlighting Circuit Test.

### Circuit/System Testing

#### Dimmer Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the S30 Headlamp Switch.
2. Ignition ON, test for greater than 11 V between the 12 V reference circuit terminal 1 and ground.

⇒ | If greater than the specified range, test the 12 V reference circuit for a short to voltage. If the circuit tests normal, replace the K9 Body Control Module (BCM).

⇒ | If less than the specified range, test the 12 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module (BCM).

3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.3 V.

⇒ | If greater than the specified range, test the signal circuit terminal 12 for a short to voltage. If the circuit tests normal, replace the K9 Body Control Module (BCM).

4. Install a 3 A fused jumper wire between the signal circuit terminal 12 and the voltage reference circuit terminal 1. Verify the scan tool Dimming Control Signal parameter is greater than 11.7 V.

⇒ | If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module (BCM).

5. If all circuits test normal, test or replace the S30 Headlamp Switch.

#### Interior Backlighting Circuit Test

1. Ignition OFF, disconnect the harness connector at the appropriate inoperative backlighting component.
2. Test for less than 5.0 Ω between the ground circuit terminal and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the control circuit terminal and ground.
4. Ignition ON, command the appropriate Incandescent Dimming or LED Dimming ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module (BCM).

⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 Body Control Module (BCM).

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

### Repair Instructions

Perform the Diagnostic Repair Verification

• | Dome Lamp Replacement

• | Sunroof Switch Replacement

• | Outside Remote Control Rearview Mirror Switch Replacement

• | Front Side Door Window Switch Replacement

• | Rear Side Door Window Switch Replacement

• | Rear Compartment Lid Release Switch Replacement

• | Steering Wheel Inflatable Restraint Module Replacement

• | Headlamp Switch Replacement

• | Parking Brake Indicator Switch Replacement

• | Steering Column Lock and Ignition Switch Cylinder Replacement

• | Hazard Warning Switch Replacement

• | Instrument Panel Multifunction Switch Replacement

• | Body Control Module Replacement

• | Steering Wheel Inflatable Restraint Module Replacement

• | Control Module References