When the ignition switch is turned to the RUN position, the radio's VF displays turn ON at maximum brightness. When the park lamps are ON, all incandescent back lighting turn ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time all VF displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the body control module (BCM). When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. The incandescent back lighting lamps are then grounded at G201, G302, and G303. When the I/P dimmer switch is moved from MIN to MAX, all vacuum fluorescent (VF) displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch.

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

Scan Tool Reference

Control Module References for Scan Tool Information

Ignition ON, observe the scan tool Dimming Input parameter while operating the dimmer switch from high to low. The voltage reading should change from high to low as the switch is rotated.

Dimmer Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the I/P Dimmer switch.
2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 10.0 ohms between the low reference circuit terminal 10 and ground.

⇒	If greater than the specified range, 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 Dimming Control Signal parameter is less than 0.1 volts.

⇒	If greater than the specified range, test the signal circuit terminal 8 for a short to voltage. If the circuit tests normal, replace the BCM.

4. Ignition ON, test for 4.8 - 5.2 volts between the 5 volt reference circuit terminal 5 and ground.

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

⇒	If more than the specified range, test the reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.

5. Install a 3A fused jumper wire between the signal circuit terminal 8 and the 5 volt reference circuit terminal 5. Verify the scan tool Dimming Input parameter displays greater than 2.5 volts.

⇒	If the parameter displays 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.

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

Interior Backlighting Malfunction

1. Ignition OFF, disconnect the harness connector at the inoperative component.
2. Test for less than 5 ohms between the listed ground circuit terminals and ground.

•	Garage door opener terminal 3

•	Sunroof switch terminal C

•	Auxiliary HVAC control module terminal A4

•	DIC switch terminal 5

•	IPC terminal A5

•	HVAC control module terminal B9 X1

•	Radio terminal B5 X1

•	Rear window wiper/washer switch terminal B

•	Interior lamp defeat switch terminal A

•	I/P dimmer switch terminal 7

•	Upper right SWC switch terminal 5

•	Upper left SWC switch terminal 3

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

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

•	Garage door opener terminal 2

•	Sunroof switch terminal B

•	Auxiliary HVAC control module terminal A5

•	DIC switch terminal 9

•	IPC terminal A7

•	HVAC control module terminal A7 X1

•	Radio terminal B4 X1

•	Rear window wiper/washer switch terminal C

•	Interior lamp defeat switch terminal B

•	IP dimmer switch terminal 6

•	Upper right SWC switch terminal 3

•	Upper left SWC switch terminal 2

4. Command the scan tool Dimming Test HIGH to LOW. The test lamp should turn from bright to dim when changing between the commanded states.

⇒	If the test lamp is always OFF, test the control circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always bright, 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 inoperative component.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.