Battery voltage is supplied at all times to the BCM from the SWITCH DM fuse located in the rear fuse block. The BCM supplies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the dimmer switch rheostat and the I/P dimming switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a variable voltage through the backlight lamp control circuits illuminating the components listed below.

The BCM detects a short to ground on the backlight lamp control circuit.

The BCM will not DIM or illuminate any backlighting supplied by the backlight lamp control circuits.

Schematic Reference

Interior Lights Dimming Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

Scan Tool Reference

Ignition ON, cover the ambient light sensor. Adjust the interior lamp dimming switch from dim to full bright. The backlighting lamps should dim and then become full bright.

1. Ignition OFF, disconnect the harness connectors at all components fed by the backlight lamp control circuits listed below.

•	Backlight lamp control terminal 18 C3

•	Backlight lamp control terminal 21 C6

2. Ignition ON, clear the DTC with a scan tool.
3. Operate the vehicle within the conditions for running the DTC and verify the DTC does not reset.

⇒	If the DTC resets, test the control circuits for a short to ground. If the circuits test normal, replace the BCM.

4. Reconnect each component one at a time and verify that the DTC does not reset as current.

⇒	If the DTC resets as current, test or replace the component responsible for setting the DTC.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.