OnStar® Microphone
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The OnStar®, or cellular, microphone on this vehicle is housed in the rearview mirror assembly. In Generation 4 equipped vehicles, the microphone is supplied 8 volts on the cellular microphone signal circuit, while Generation 5 equipped vehicles supply the microphone 10 volts. Voice data from the user is sent back to the VCIM by means of either a cellular microphone low reference circuit or a drain wire.