Class 2 Data Line

U.S Federal regulations require that all automobile manufacturers establish a common communications system. General Motors utilizes the Class 2 communications system.

Class 2 serial data is transferred at a rate of 10,400 bits per second, and the voltage is toggled between 0 and 7 volts. When communication is not occurring on the data line the voltage is zero or ground and is switched to 7 volts when active.

Class 2 data is also pulse width modulated. Each bit of information can have one of two lengths: long or short. The pulse width modulation of Class 2 data allows better utilization of the data line.

The messages carried on Class 2 data streams are also prioritized. This means if two devices try to communicate on the data line at the same time, only the higher priority message will continue. The device with the lower priority message must wait. The modules on the Class 2 data line are:
^ Body Control Module (BCM)
^ Cellular Telephone
^ Radio Receiver
^ Remote Control Door Lock Receiver (1st design)
^ Sound Processor Interface