Theory Of Operation
WARNING: This page is about a different car, the 2016 Dodge Durango. However, it is still accessible from the selected car via links, so may be relevant.
The driver electrochromatic mirror is controlled by the Body Control Module (BCM). The BCM receives the dimming control from the sensor in the Interior Rearview Mirror. The BCM send a Bus message to the Passenger Door Module (DDM) which turns the dimming on and off. At night the dimming will be cancelled when the vehicle is in reverse.