Vehicle Interface Unit (Viu)

The Vehicle Interface Unit for the OnStar(R) system contains a GPS receiver and a cellular modem. The GPS receiver determines the vehicle location using the GPS satellite system. The GPS signal receiving antenna, or navigation antenna, plugs directly into the VIU and requires a clear and unobstructed path to the satellites in the sky. Window tinting applied to vehicle glass may interfere with the navigation antenna functions depending upon the amount of darkening and/or metallic particles which are embedded in the darkening film of the tinting material. The VIU communicates with the rest of the vehicle over the class 2 serial data bus. Power is supplied to the VIU from the battery positive voltage circuit and power moding is achieved by means of class 2 messaging. Class 2 is also used for features such as impact detection, door lock and unlock, horn pulse, light flash, audio mute, and remote diagnostics. After the audio system has muted, the OnStar(R) audio is transmitted to the vehicle audio system on the remote audio output (-), remote audio right signal circuit, and the remote audio left signal circuit.