Circuit/System Description
WARNING: This page is about a different car, the 2013 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
The Radio interfaces only with the Info Display Module and the Info Display Module communicates with the Radio/HVAC Control through a Linear Interconnect Network (LIN) interface. The Info Display Module is responsible for passing information between the Radio and the Radio/HVAC Control.