Description & Operation

WARNING: Vehicles are equipped with air bag supplemental restraint system. Before attempting ANY repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in appropriate AIR BAG RESTRAINT SYSTEMS article.

The Body Control Module (BCM) communicates with the following modules over the class-2 serial data line to control various functions.

Powertrain Control Module (PCM)
Electronic Brake/Traction Control Module (EBTCM)
Sensing & Diagnostic Module (SDM)

Some vehicle systems share data over a serial data line to execute various vehicle functions. Powertrain Control Module (PCM) will generate a message on class-2 serial data line which can be read by any other controller. Each class-2 module is programmed with a list of important serial data messages that should be received by other modules. Also contained are default actions taken by the module if one of the important messages is not received in time. One of these messages is the State Of Health (SOH) message. SOH is sent out periodically (if no other message needs to be sent) to let all other modules on serial data line know the sending module is working correctly.

Each controller relies on information from another controller and incorporates a diagnostic associated with that controller. The diagnostic uses the SOH message to perform a diagnostic. Each time ignition is turned on, all modules on class-2 serial data line learn the other modules connected to class-2 serial data line. Modules are able to learn other modules on serial data line because each important message sent has a source identifier as part of the message.