Circuit/System Description
WARNING: This page is about a different car, the 2012 Buick LaCrosse. However, it is still accessible from the selected car via links, so may be relevant.
The antenna module receives both AM and FM signals from the rear glass antenna. The radio antenna module is enabled when the radio is turned on. The radio provides battery voltage to the antenna module using the center conductor of the antenna coaxial cable. When a 12 V signal is seen by the module on the center conductor of the antenna coax, both AM and FM signals are amplified.