Circuit/System Description
WARNING: This page is about a different car, the 2007 Pontiac Montana SV6, 2007 Chevrolet Uplander, and 2007 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
The vehicle communication interface module (VCIM) detects that the cellular microphone is connected through the cellular microphone signal circuit and the drain wire.