When the headlamp switch is placed in either the HEAD or PARK position, ground is applied to the park lamp signal circuit to the body control module (BCM). The BCM responds by applying ground to the park lamp relay control circuit. This energizes the park lamp relay coil causing the relay switch contacts to close allowing battery voltage to flow to all of the park, tail, license, marker lamps, interior ambient lighting, and to the BCM. The BCM receives the voltage from the park lamp relay indicating the park lamps are ON. The BCM uses this signal to command the interior backlighting ON and OFF. 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 B+ voltage signal and a low 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 indicator dimming control circuit and the interior backlighting components dim to the requested level.

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

1. Ignition ON, command the Parking Lamps ON and OFF with a scan tool. The park lamps should turn ON and OFF when changing between the commanded states.

⇒	If the park lamps do not illuminate when commanded, refer to Park, License, and/or Tail Lamps Malfunction.

2. Ignition ON, observe the scan tool I/P Dimmer Switch parameter while operating the dimmer switch from high to low. The voltage reading should change as the switch is activated.

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

3. Park lamps ON, with a scan tool, perform the Incandescent Dimming test. The interior backlighting should illuminate from high to low for all components controlled by the I/P dimming control circuit.

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

4. Park lamps ON, with a scan tool, perform the LED Dimming test. The interior backlighting should illuminate from high to low for all components controlled by the LED dimming control circuit.

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

Dimmer Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
2. Ignition OFF, verify that a test lamp illuminates between the ground circuit terminal 8 and B+.

⇒	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 13 for a short to voltage. If the circuit tests normal, replace the BCM.

4. Ignition ON, test for B+ between the I/P dimming voltage reference circuit terminal 15 and ground.

⇒	If less than the specified value, test the B+ 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 13 and the voltage reference circuit terminal 15. Verify the scan tool BCM Dimming Control Signal parameter is greater than 2.6 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 headlamp and panel dimmer switch.

Interior Backlighting Malfunction

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

•	Automatic Transmission Shift Lever Position Lamp terminal B

•	Global Window Switch terminal D

•	Transfer Case Control Switch terminal 6

•	Headlamp and Panel DImmer Switch terminal 8

•	Midgate Window Switch terminal D

•	Sunroof Switch terminal C

•	Rear Window Switch terminal E

⇒	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.

•	Automatic Transmission Shift Lever Position Lamp terminal A

•	Global Window Switch terminal E

•	Transfer Case Control Switch terminal 5

•	Headlamp and Panel DImmer Switch terminal 7

•	Midgate Window Switch terminal E

•	Sunroof Switch terminal A

•	Rear Window Switch terminal A

4. Command the dimming test high to low with a scan tool. 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 a short to ground or an open/high resistance. 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.

LED Backlighting Malfunction

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

•	Left Steering Wheel Switch terminal 8

•	Right Steering Wheel Switch terminal 1

•	Analog Clock terminal 2

•	Rear Wiper/Washer Switch terminal 1

•	DIC Switch terminal 5

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

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

•	Left Steering Wheel Switch terminal 2

•	Right Steering Wheel Switch terminal 6

•	Analog Clock terminal 3

•	Rear Wiper/Washer Switch terminal 4

•	DIC Switch terminal 4

•	Instument Panel Cluster terminal 8

•	Radio terminal 7

4. Command the dimming test high to low with a scan tool. 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 a short to ground or an open/high resistance. 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.