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
--- | --- | --- | --- | ---
I/P Dimmer Switch Signal | B3600 03 | B3600 03 | B3600 07 | --
Headlamp Switch Backlighting Control | 2 | 2 | 2 | --
LED Backlight Dimming Control | B2610 02 | 1 | B2610 01 | --
Headlamp Switch Low Reference | -- | 1 | -- | --
Headlamp Switch Ground | -- | 2 | -- | --
1. Interior Backlighting Malfunction - Dimming 2. Headlamp Switch Backlighting Malfunction

### Circuit/System Description

The instrument panel (I/P) lamp dimmer switch is incorporated into the headlamp switch assembly. The I/P 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 instrument panel cluster (IPC) provides a low reference signal and a 12 volt 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 IPC. The IPC 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 the headlamp switch low reference circuit through the IPC.

### 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 Switch Illumination Dimming parameter while operating the dimmer switch from high to low. The parameter should change from Dark to Bright as the switch is activated.

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

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

### Circuit/System Testing

#### I/P Dimmer Switch Malfunction

1. With a scan tool clear the DTC.
2. Ignition OFF, disconnect the harness connector at the headlamp switch.
3. Ignition OFF, verify a test lamp illuminates between B+ and the low reference circuit terminal 11.

⇒ | If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPC.

4. Verify the scan tool Switch Illumination Dimming parameter displays Disabled or Invalid.

⇒ | If not the specified value, test the signal circuit terminal 4 for a short to voltage. If the circuit tests normal, replace the IPC.

5. Install a 3A fused jumper wire between the signal circuit terminal 4 and the low reference circuit terminal 11. Verify the scan tool Switch Illumination Dimming parameter displays Bright or Dark.

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

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

#### Interior Backlighting Malfunction - Dimming

1. Ignition OFF, disconnect the harness connector at the component with the inoperative dimming LED 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.

• | Transmission range selector indicator ground terminal 2

• | Dome lamp switch - front ground terminal 5

• | Hazard switch ground terminal 2

• | HVAC control module ground terminal 1

• | Sunroof control module ground X2 terminal 1

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

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

• | Transmission range selector indicator dimming control terminal 7

• | Dome lamp switch - front dimming control terminal 14

• | Hazard switch dimming control terminal 18

• | HVAC control module dimming control terminal 2

• | Sunroof control module dimming control X1 terminal 14

4. Command the Dimmed Illumination Control 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 appropriate control module.

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

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

#### Headlamp Switch Backlighting Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition OFF, verify a test lamp illuminates between B+ and the ground circuit terminal 6.

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

3. Ignition OFF, verify a test lamp does not illuminate between the control circuit terminal 7 and ground.

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage.

4. Ignition ON, verify a test lamp illuminates between the control circuit terminal 7 and ground.

⇒ | If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Dome Lamp Replacement

• | Headlamp Switch Replacement

• | Overhead Console Reading Lamp and Bulb Replacement

• | Front Seat Heater Switch Replacement

• | Automatic Transmission Range Selector Lever Replacement

• | Control Module References for HVAC Control Module, IPC, or REC replacement, setup, and programming