Door Modules
WARNING: This page is about a different car, the 2009 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
The driver and passenger receive serial data messages from the side object sensors. When a message is received indicating that a vehicle or object is in the blind spot, the appropriate door module will apply voltage to the indicator located in the outside rearview mirror, illuminating the indicator. The door module provides a continuous low reference circuit for the indicator.