Circuit/System Description
WARNING: This page is about a different car, the 2007 Buick LaCrosse and 2007 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
The steering wheel control signal circuit applies a different voltage to the radio based on a resistance that is placed into the circuit when a steering wheel control switch is pressed. These different voltage levels signal the radio to do the appropriate function based on the steering wheel button pressed.