Vehicle Interface Unit (VIU)

The VIU for the OnStar(R) system contains a GPS receiver and a cellular modem. The GPS receiver determines the vehicles location using the GPS satellite system. The GPS antenna plugs directly into the VIU. The GPS antenna requires a clear and unobstructed path to the satellites in the sky. Window tinting to vehicles which may interfere with the GPS sensor functions. Depending on the amount of darkening and/or metallic particles which are embedded in the darkening film of the tinting material, GPS sensor performance may be compromised. The VIU communicates with the rest of the vehicle over the class 2 serial data bus. On vehicles that do not use class 2 to communicate with the audio system the VIU uses the entertainment and comfort serial data circuit. The VIU is supplied power from the battery positive voltage circuit. Power moding for the VIU is accomplished by a class 2 message on some vehicles or the ignition 1 voltage circuit on others. The VIU also has the capability of commanding the horn, door unlock and exterior lamps using the class 2 serial data circuit. For vehicles without that capability, the VIU uses specific circuits for commanding the horn, door unlock and exterior lamps. To mute the audio system the VIU uses either the class 2 serial data circuit on some vehicles and others use the entertainment and comfort serial data circuit. After the audio system is muted the OnStar(R) audio is transmitted to the vehicles audio system on the remote audio output (-), remote audio right signal circuit, and the remote audio left signal circuit.