Principles of Operation

Communications Network

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

Vehicle communication utilizes both Medium Speed (MS) and High Speed (HS) Controller Area Network (CAN) communications. CAN is a method for transferring data among distributed electronic modules via a serial data bus.

The vehicle is equipped with 2 module communication networks:

- High Speed (HS) CAN
- Medium Speed (MS) CAN

High Speed Controller Area Network (HS-CAN) and Medium Speed Controller Area Network (MS-CAN)

CAN is a communication network that uses an unshielded twisted pair cable of data (+) and data (-) circuits. The data (+) and the data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As bus messages are sent on the data (+) circuit, voltage is increased by approximately 1.0 volt. Inversely, the data (-) circuit is reduced by approximately 1.0 volt when a bus message is sent. Multiple bus messages can be sent over the network CAN circuits allowing multiple modules to communicate with each other.

The MS-CAN operates at a maximum data transfer speed of 125 Kbps for bus messages and is designed for general information transfer. The HS-CAN operates at a maximum data transfer speed of 500 Kbps and is designed for real time information transfer and control.

Certain network faults may cause inconsistent message communication. The CAN may remain operational with only 1 of the 2 termination resistors present.

The following fault chart describes the specific CAN failures and their resulting symptom:

CAN Communication Fault Chart:

The following chart describes the specific HS-CAN messages broadcast by each module, and the module(s) that receive the message:

NOTE: Network DTCs which are not listed in the below chart either relate to an invalid data concern (the message is not missing but the data value sent not within acceptable range) or indicate an entire network bus outage concern which is not specifically related to missing data from certain modules, i.e. the network is open or shorted.

Refer to the network DTC charts for specific DTC information and recommended action. Diagnostic Trouble Code Tests and Associated Procedures

Module Communication Message Chart (1 Of 4):

Module Communication Message Chart (2 Of 4):

Module Communication Message Chart (3 Of 4):

Module Communication Message Chart (4 Of 4):