Electronic Control Modules (Service Information): Communication: Operation

The Controller Area Network (CAN) data bus allows all ECUs (Electronic Control Units) connected to the bus to share information with each other. Regardless of whether a message originates from a ECU on the lower speed CAN-B bus or on the higher speed CAN-C bus, the message structure and layout is similar, which allows the Body Control Module (BCM) to process and transfer messages between the CAN buses. The BCM also stores a Diagnostic Trouble Code (DTC) for certain bus network faults. These networks and their subnetworks are protected by a Security Gateway Module (SGM).

The CAN-C bus modules are connected in series-parallel (daisy chained) having an internal connection that completes the CAN circuit. The CAN is still a series-parallel circuit, however, each module must remain connected in order to complete the circuit and multiple modules will lose communication if one is disconnected. As long as the communication circuit connections are complete, the network can communicate even if an individual module is not functional. Modules that lose communication with the vehicle due to loss of power, ground, or internal failure will not prevent other modules from communicating. A single non-communicating module in the middle of the bus can be attributed to a loss of power or ground, or an internal failure and is not the result of an open or shorted bus circuit. A unique characteristic for the daisy chain configuration is that when an open circuit is present in either of the bus circuits, multiple modules will be affected. The only exception to this is the last module on the bus; in which case there are no other modules that rely on the throughput circuitry to connect to the bus. However, since the module on the end is a dominant module, total network communication may be affected. As with other networks, when a short is present anywhere on the bus, the entire network will lose communication.

All ECUs transmit and receive messages over one of these buses. Data exchange between nodes is achieved by serial transmission of encoded data messages. Each node can both send and receive serial data simultaneously. Each digital bit of a CAN bus message is carried over the bus as a voltage differential between the two bus circuits which, when strung together, form a message. Each node uses arbitration to sort the message priority if two competing messages are attempting to be broadcast at the same time.

The Controller Area Network (CAN) data bus allows all electronic modules or nodes connected to the bus to share information with each other. Regardless of whether a message originates from a module on the lower speed CAN-B bus or on the higher speed CAN-C bus, the message structure and layout is similar, which allows the Body Control Module (BCM) to process and transfer messages between the CAN buses. The BCM also stores a Diagnostic Trouble Code (DTC) for certain bus network faults.

Refer to the appropriate SYSTEM WIRING DIAGRAM COMMUNICATION section to view the bus topologies and ECU bus assignments.