Circuit/System Description
WARNING: This page is about a different car, the 2011 Chevrolet Caprice. However, it is still accessible from the selected car via links, so may be relevant.
The radio monitors the button presses on the Radio/HVAC control. The radio will ignore any stuck buttons and allow full functionality of the working buttons. The only circuit required is the serial data line between the radio and the Radio/HVAC control.