Interior Backlighting Does Not Dim

INTERIOR BACKLIGHTING DOES NOT DIM




DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
The body control module (BCM) receives an input from the instrument panel (I/P) dimmer switch. The BCM provides the I/P dimmer switch with battery positive voltage and ground. The I/P dimmer switch is a potentiometer that varies the input signal voltage to the BCM. This input determines the intensity level of the backlighting illumination. The driver may change intensity of the backlighting by positioning the I/P dimmer switch between the minimum and maximum settings. The BCM will default to full intensity if the input from the I/P dimmer switch is not within the specified values. The backlighting illumination intensity is controlled by the BCM by varying the pulse width modulation (PWM) voltage that feeds the dimming signal circuits of the individual lamps. All interior backlighting lamps are permanently grounded.

CIRCUIT/SYSTEM TESTING
1. Ignition ON, install a scan tool and observe the I/P Dimmer Switch voltage parameter while rotating the I/P dimmer switch. The voltage parameter should change as the switch is rotated from min to max.
- If the I/P Dimmer Switch voltage parameter changes as the I/P dimmer switch is rotated, repair the I/P lamp supply voltage circuit for a short to voltage. If the circuit tests normal, replace the BCM.
- If the I/P Dimmer switch voltage parameter does not change as the I/P dimmer switch is rotated, test the I/P lamp dimmer switch signal circuit for a short to ground or an open/high resistance.
- If the I/P lamp dimmer switch signal circuit tests normal, test the I/P dimmer switch low reference circuit for a short to voltage or an open/high resistance.
2. If all circuits test normal, test or replace the I/P dimmer switch.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

- Instrument Panel (I/P) Dimmer Switch Replacement
- Control Module References for BCM replacement, setup, and programming