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 B3600 03: Passenger Compartment Dimming Request Signal Circuit Voltage Below Threshold

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
12-Volt Reference | B1395 03, B3600 03 | B3600 03 | 2 | B1395 07
I/P Dimming Signal | B3600 03 | B3600 03 | 1 | --
1. Interior Backlighting Inoperative 2. Interior Backlighting Will Not Dim

### Circuit/System Description

The instrument panel (I/P) dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The body control module (BCM) supplies a 12-volt reference through the instrument panel (I/P) 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 I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the I/P 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-volt reference circuit.

• | The BCM detects a short to ground or open in the I/P 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 I/P lamps should dim and then become full bright.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition ON, test for 11.8-12.2 volts between the 12-volt reference circuit terminal 15 and ground.

⇒ | If greater than the specified range, test the 12-volt reference circuit for short to voltage. If the circuit tests normal, replace the BCM.

⇒ | If less than the specified range, test the 12-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

3. Verify the scan tool Dimming Control Signal parameter is less than 0.75 volts.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal 13 and the 12-volt reference circuit terminal 15. Verify the scan tool Dimming Control Signal parameter is greater than 11.294 volts.

⇒ | 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 BCM.

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