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.

A short to ground condition located anywhere in the indicator dimming control circuit (8 GY) or the park lamps control circuit (9 BN) will cause the park lamps fuse to open.

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 parameter should change as the switch is activated.

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

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

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

I/P Dimmer Switch Malfunction

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

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

3. Ignition ON, park lamps ON, test for B+ between the signal circuit terminal C and ground.

⇒	If 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.

4. Install a 3A fused jumper wire between the signal circuit terminal C and the low reference circuit terminal D. Verify the scan tool IP Dimmer Switch parameter is less than B+.

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

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

Interior Backlighting Malfunction

1. Ignition OFF, disconnect the harness connector at the component with the inoperative backlighting.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit and ground.

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

3. Connect a test lamp between the control circuit and ground.
4. Park lamps ON, command the Interior Dimming the Increase and Decrease with a scan tool. The test lamp brightness should increase and decrease 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 incandescent backlighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.