CAN Serial Data Circuit

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The controller area network (CAN) serial data line is used for functional messages only and does not communicate with the scan tool via the data link connector (DLC). The identifier labels both the data content and the priority of the message being sent. Each module can begin transmitting its most important data as soon as the bus is unoccupied. When more than one module starts to transmit simultaneously, the message with the highest priority is assigned first access. A module responds to failure to gain access by automatically switching to receive mode, the module then repeats the transmission attempt as soon as the bus is free again.

The body control module (BCM) acts as gateway between CAN and class 2 serial data lines, transmitting messages from one subnet to another. The BCM emulates the CAN modules on the class 2, embedding the original transmitter ID in translated CAN messages to class 2. Therefore the class 2 modules can set specific non communications DTCs against CAN modules. This concept doesn't apply for class 2 to CAN transmitted messages. Therefore the CAN modules consider the BCM as being the originator of all class 2 messages that they receive. The following modules communicate on the CAN serial data line:

Electronic brake control module (EBCM)
Transmission control module (TCM), w/L61
Engine/powertrain control module (ECM/PCM)