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 Descriptors

DTC B3600 03: Passenger Compartment Dimming Request Signal Circuit Low Voltage
DTC B3600 07: Passenger Compartment Dimming Request Signal Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
12-Volt Reference | B1395 03, B3600 03 | B3600 03 | B3600 03** | B1395 07
I/P Dimming Signal | B3600 03 | B3600 03 | B3600 07* | --
* Interior Backlighting Inoperative ** Interior Backlighting Will Not Dim

### Circuit/System Description

The instrument panel dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The body control module (BCM) supplies a 12 V reference through the instrument panel dimming voltage reference circuit to the interior lamp 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 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 lamps control circuit and the LED dimming control circuit to all related interior lamps, illuminating them to the desired level of brightness.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

• | The BCM detects a short to ground or open in the 12 V reference circuit.

• | The BCM detects a short to ground or open in the instrument panel dimming signal circuit.

### Action Taken When the DTC Sets

The I/P lamps are not illuminated.

### Conditions for Clearing the DTC

A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

### 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, cover the ambient light sensor, vary the interior lamp dimming switch from dim to full bright. The instrument panel lamps should dim and then become full bright.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the S30 Headlamp Switch.
2. Ignition ON, test for 11.8-12.2 V between the 12 V reference circuit terminal 1 and ground.

⇒ | If greater than the specified range, test the 12 V reference circuit for 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. Verify the scan tool Incandescent Dimming parameter is less than 10 percent.

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

4. Install a 3A fused jumper wire between the signal circuit terminal 12 and the 12 V reference circuit terminal 1. Verify the scan tool Incandescent Dimming parameter is greater than 90 percent.

⇒ | If less than the specified value, 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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Switch Replacement

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