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
--- | --- | --- | --- | ---
Instrument Panel Lamps Dimmer Switch Signal | 2 | 2 | -- | --
Park Lamp Control | 3 | 1 | 3 | --
Instrument Panel Lamps Control | B2625 02 | 1 | 1 | --
Instrument Panel Lamps Dimmer Switch Low Reference | 2 | 2 | 2 | --
1. Interior Backlighting Malfunction 2. Dimmer Switch Malfunction 3. Park, License, and/or Tail Lamps Malfunction

### Circuit/System Description

The body control module (BCM) receives an input from the instrument panel (I/P) dimmer switch. The BCM provides the I/P dimmer switch with battery voltage and a low reference. The I/P dimmer switch is a potentiometer that varies the input signal voltage to the BCM. This input determines the intensity level of the backlighting illumination. The driver may change intensity of the backlighting by positioning the I/P dimmer switch between the minimum and maximum settings. The BCM will default to full intensity if the input from the I/P dimmer switch is not within the specified values. The backlighting illumination intensity is controlled by the BCM by varying the pulse width modulation (PWM) voltage that feeds the dimming signal circuits of the individual lamps. All interior backlighting lamps are permanently grounded.

### 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 IP Dimmer Switch parameter while activating the switch from min to max. The voltage parameter should change as the switch is cycled between the min and max settings.

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

⇒ | If the parameter changes, refer to Interior Backlighting Malfunction.

### Circuit/System Testing

#### Interior Backlighting Malfunction

1. Ignition ON, install a scan tool and observe the Interior Light Dimmed Command parameter while turning the parks lamps ON and OFF. The reading should change between Off and On.

⇒ | If the parameter is always ON, test the park lamp supply voltage circuit at the X3 BCM harness connector terminal A7 for a short to voltage. If the circuit tests normal, replace the BCM.

⇒ | If the parameter is always OFF, test the park lamp supply voltage circuit at the X3 BCM harness connector terminal A7 for a short to ground or and open/high resistance. If the circuit tests normal, replace the BCM.

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

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

4. Connect a test lamp between the instrument panel lamp supply control circuit that supplies the inoperative component lamp and ground.
5. Command the park lamps ON and OFF with the park lamps switch. 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 BCM.

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

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

#### Dimmer Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the I/P dimmer switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the low reference circuit terminal B.

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

3. Ignition ON, verify the scan tool I/P Dimmer Switch parameter is greater than 12 volts.

⇒ | If not the specified value, test the signal circuit terminal C 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 C and the low reference circuit terminal B. Verify the scan tool I/P dimmer switch is less than 11 volts.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPC.

5. If all circuits test normal, test or replace the I/P dimmer switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Electronic Traction Control Switch Replacement

• | Front Side Door Window Switch Replacement

• | Radio Replacement

• | Instrument Cluster Replacement

• | Fog Lamp Switch Replacement

• | Hazard Warning Switch Replacement

• | Instrument Panel Lamp Dimmer Switch Replacement

• | Heater and Air Conditioning Control Replacement

• | Power Mirror Switch Replacement

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