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
--- | --- | --- | --- | ---
CHMSL/DM/LAMP Fuse B+ | B2610 00 | B2610 00 | -- | --
Dimmer Switch B+ Voltage Reference | 1 | 1 | -- | --
Dimmer Switch Signal | B1395 03, B3600 03 | B2652 00, B3600 03 | B1395 07 | --
I/P Lamps Control | B2652 00 | 1 | 1 | --
Incandescent Backlight Dimming Control | 2 | 2 | 2 | --
LED Backlight Dimming Control | B2610 00 | 3 | 3 | --
Dimmer Switch Ground | -- | 1 | -- | --
1. Dimmer Switch Malfunction 2. Interior Backlighting Malfunction -- Incandescent 3. Interior Backlighting Malfunction -- LED

### Circuit/System Description

The instrument panel (I/P) lamp 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. Ground for the I/P dimmer switch is provided at G201.

### 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

1. Ignition ON, observe the scan tool Dimming Control Signal parameter while operating the dimmer switch from high to low. The parameter should change from a high percent to a low percent as the switch is activated.

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

2. Command the Incandescent Dimming ON and OFF with a scan tool. The incandescent backlighting should illuminate from high to low.

⇒ | If the backlighting does not operate as described, refer to Interior Backlighting Malfunction.

3. Command the LED Dimming ON and OFF with a scan tool. The LED backlighting should illuminate from high to low.

⇒ | If the backlighting does not operate as described, refer to Interior Backlighting Malfunction.

### Circuit/System Testing

#### Dimmer Switch Malfunction

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

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

3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.1 volts.

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

4. Ignition ON, test for B+ between the voltage reference circuit terminal D and ground.

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

5. Install a 3A fused jumper wire between the signal circuit terminal B and the voltage reference circuit terminal D. Verify the scan tool Dimming Control Signal parameter is greater than 2.5 volts.

⇒ | 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 BCM.

6. If all circuits test normal, test or replace the dimmer switch.

#### Interior Backlighting Malfunction

1. Ignition OFF, disconnect the harness connector at the component with the inoperative backlighting.
2. Ignition OFF, scan tool OFF, interior lamps OFF, doors CLOSED, test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground:

• | Driver information center terminal 5

• | Driver window switch terminal 6 X2

• | Hazard switch terminal J

• | HVAC control module terminal 10 X1

• | Radio terminal 8 X1

• | Rear window wiper/washer/fog lamp switch terminal 5

• | Steering wheel control switch - left terminal 8

• | Steering wheel control switch - right terminal 4

• | Traction control switch terminal 2

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

3. Connect a test lamp between the appropriate control circuit terminal listed below and ground:

• | Driver information center terminal 4

• | Driver window switch terminal 2 X1

• | Hazard switch terminal I

• | HVAC control module terminal 1 X1

• | Radio terminal 7 X1

• | Rear window wiper/washer/fog lamp switch terminal 6

• | Steering wheel control switch - left terminal 6

• | Steering wheel control switch - right terminal 3

• | Traction control switch terminal 3

4. 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 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.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Front Side Door Window Switch Replacement

• | Instrument Panel Lamp Dimmer Switch Replacement

• | Hazard Warning Switch Replacement

• | Fog Lamp Switch Replacement

• | Driver Information Display Switch Replacement

• | Steering Wheel Control Switch Assembly Replacement

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