Class 2 Data Line

The Class 2 data line is powered by the modules that are connected to it during operation. Communication on the Class 2 data line occurs on an as needed basis, rather than being a continuous stream of data. Information is transmitted in bits, with each bit indicating status that is either low (0 volts) or high (7 volts). When no communication is occurring on the Class 2 data line, voltage is low. Class 2 data is transmitted at a higher speed and messages are configured differently than UART data. Class 2 uses the peer to peer method along with message arbitration to manage data line traffic. The control modules on the Class 2 data line are as follows:

• Body Control Module (BCM).
• Instrument cluster.
• Automatic Transfer Case (ATC) control module.
• Vehicle Control Module (VCM).
• Powertrain Control Module (PCM).
• Electronic Brake Control Module (EBCM).

Modules connected to the Class 2 serial data link monitor the link for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for state of health monitoring (Node Alive messages). A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter.