With the park lamps ON, the body control module (BCM) receives B+ voltage from the PARK LAMP relay indicating the parks lamps are ON. The instrument panel (I/P) lamp dimmer switch is used to increase and decrease the brightness of the interior backlighting components. With the park lamps ON, 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 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 indicator dimming control circuit and the interior backlighting components dim to the requested level.

Schematic Reference

Interior Lights Dimming Schematics

Description and Operation

Interior Lighting Systems Description and Operation

Electrical Information Reference

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 turn ON and OFF when commanded, refer to Park, License, and/or Tail Lamps Malfunction .

2. Command the Interior Dimming control ON and OFF with a scan tool. The interior backlighting should change from low to high when changing between the commanded states.

⇒	If the interior backlighting does not illuminate from LOW to HIGH when commanded, refer to Interior Backlighting Malfunction.

3. Observe the interior backlighting while operating the I/P dimmer switch from high to low. The interior backlighting should change from low to high as the switch is operated.

⇒	If the interior backlighting does not change when commanded, refer to I/P Dimmer Switch Malfunction.

I/P Dimmer Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the I/P dimmer switch.
2. Install a 3A fused jumper wire between the signal circuit terminal C and ground.
3. Ignition ON, park lamps ON, verify the interior backlighting illuminates.

⇒	If the interior backlighting does not illuminate, 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. The interior backlighting should illuminate.

⇒	If the interior backlighting does not illuminate, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

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

Interior Backlighting Malfunction

1. Ignition OFF, disconnect the X3 harness connector at the BCM.
2. Connect a test lamp between the control circuit terminal A7 and ground.
3. Command the Parking Lamps 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 ON, test the control circuit for a short to voltage.

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

4. Ignition OFF, connect the X3 harness connector at the BCM.
5. Disconnect the harness connector at the component with the inoperative backlighting.
6. Ignition OFF, scan tool OFF, interior lamps OFF, doors CLOSED, 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.

7. Connect a test lamp between the control circuit and ground.
8. Command the Interior Dimming 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 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.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.