Circuit Description
WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
The OnStar® button assembly consists of three buttons, Call/Answer, OnStar® Call Center and OnStar® Emergency. Ten volts is supplied to the button assembly on the Keypad Supply Voltage circuit. Each of the buttons, when pressed, completes the circuit across a resister allowing a specific voltage to be returned to the Vehicle Communication Interface Module on the keypad signal circuit. Depending upon the voltage range returned, the Vehicle Communication Interface Module is able to identify which button has been pressed.