OnStar

OnStar is a new on-vehicle communications system which is a dealer installed option. The BCM acts as the interface between the OnStar and the vehicle architecture. It receives the following Class 2 messages from the Vehicle Interface Unit (VIU).
^ Door unlock or lock activation
^ Horn control
^ Interior light control
^ Exterior lighting; activates the parklamps and lowbeams. In the event the exterior lamps are active due to either DRL, twilight sentinel or wiper-on lighting, the message sent from the VIU will override these modes, turning the parklamps or lowbeams On or Off as required.

The BCM is hard wired (CKT XY999) to the Inflatable Restraint Sensing Module. After the ignition is turned to the On position, the restraint module sends voltage pulses as a test message to the BCM. When an airbag deployment has occurred, the BCM continues to receive the voltage pulses but at a greater number and repetitive rate. The BCM then sends a Class 2 message to the VIU that a restraint system was activated.