Vehicle Communication Unit (VCU)

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 Chevrolet Tahoe, 2002 Chevrolet Suburban, and 2002 Cadillac Escalade EXT. However, it is still accessible from the selected car via links, so may be relevant.

The Vehicle Communication Unit (VCU) is a 3 watt cellular transceiver that connects the OnStar® system to the cellular carrier's communication system. This module handles all cellular operations, sending and receiving all communications over the cellular antenna and cellular antenna coax. Power and ground for the VCU is provided by the VIU on the battery positive voltage and ground circuits. The VIU also supplies ignition voltage to the VCU over the ignition 1 voltage circuit. The VCU communicates with the VIU by using the OnStar® serial data (-) circuit, OnStar® serial data (+) circuit and the OnStar® 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.