Control module. OnStar, VCIM (673): General

The main unit in the OnStar system is the VCIM (Vehicle Communication Interface Module). The VCIM incorporates a mobile telephone and a GPS receiver. The unit is connected to the OIM (OnStar Interface Module), radio, microphone, control button unit, GPS/mobile telephone antenna and data link connector via the car's wiring harness. The VCIM is fitted with one 12 pin and one 16 pin connector.

The main functions of the system are as follows:

• To communicate voice and data over the mobile phone network.
• To receive data signals from the GPS and the calculation of the car's position. The position of the car is sent using data communication to the OnStar Call Center.
• To transmit bus messages to the OIM (OnStar Interface Module) for the activation of the car's horn and hazard warning lights.
• To receive bus messages from the OIM when airbags are activated in order to automatically phone for assistance.
• To relay telephone conversations via the system speakers.
• To switch off other sound from the audio system when making a telephone call. This is effected by feeding a "mute" signal from the VCIM to the audio unit which then disconnects the non-conversational inputs to the speakers and to any external amplifiers.
• Diagnostic communication.