Controller Area Network (CAN) Serial Data Line w/M82

WARNING: This page is about a different car, the 2004 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.

The Controller Area Network (CAN) serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the engine control module (ECM) and transmitted to the class 2 serial data line by the ECM. The following modules communicate on the CAN serial data line:

The ECM w/LA3/LY9
The TCM w/LA3/LY9

The CAN serial data line is high speed serial data bus used to communicate information between the engine control module (ECM) and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure that the required real-time response is maintained.

The addressing scheme employed with CAN assigns a label to every message, with each message receiving a unique identifier. The identifier classifies the content of the message. Each module processes only those messages whose identifiers are stored in the module's acceptance list. This is CAN's form of message filtering.

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.