Circuit/System Description
WARNING: This page is about a different car, the 2011 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) supplies a voltage reference to the 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 to the BCM. The BCM interprets this voltage signal, then applies a variable voltage through the LED backlight lamp control circuit.