Vehicle Communication Unit (VCU)

The Vehicle Communication Unit is a 3-watt transceiver that connects the OnStar(R) system to the cellular carriers communication system. The cellular antenna plugs directly into the VCU while power and ground is provided by the Vehicle Interface Unit (VIU). Communication between the VIU and VCU is accomplished via the OnStar(R) serial data (-) circuit, OnStar(R) serial data (+) circuit, and the serial data return circuit. The callers voice is carried to the VCU using the microphone signal circuit and the drain wire circuit. The audio signal is carried from the VCU to the VIU on the audio return signal circuit and the audio low reference circuit.