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:

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

Medium Speed Controller Area Network (MS-CAN)

The MS-CAN is a medium speed 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 will not communicate while certain faults are present, but will operate with diminished performance with other faults present. The MS-CAN may remain operational when 1 of the 2 termination resistors are not present.

The MS-CAN operates at a maximum data transfer speed of 125 Kbps for bus messages and designed for general information transfer. The network will remain operational, but at a degraded level, when certain circuit faults are present.

The following modules are on the MS-CAN:

- Accessory Protocol Interface Module (APIM) (if equipped)
- Audio Control Module (ACM)
- Driver Seat Module (DSM) (if equipped)
- HVAC module (if equipped)
- Instrument Cluster (IC)
- Parking Aid Module (PAM) (if equipped)
- Power Running Board (PRB) module (if equipped)
- Rear Entertainment Module (RETM) (if equipped)
- Satellite Digital Audio Receiver System (SDARS) module (if equipped)
- Smart Junction Box (SJB)

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

Medium Speed Controller Area Network (MS-CAN) Communication Fault Chart:

High Speed Controller Area Network (HS-CAN)

The HS-CAN is a high speed 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 HS-CAN will not communicate while certain faults are present, but will operate with diminished performance with other faults present. The HS-CAN bus may remain operational when 1 of the 2 termination resistors are not present.

The HS-CAN operates at a maximum data transfer speed of 500 Kbps and is designed for real time information transfer and control. The network will remain operational, but at a degraded level, when certain circuit faults are present.

The following modules are on the HS-CAN:

- 4X4 control module (if equipped)
- ABS module
- Accessory Protocol Interface Module (APIM) (if equipped)
- Instrument Cluster (IC)
- Occupant Classification System Module (OCSM)
- PCM
- Restraints Control Module (RCM)
- Transmission Control Module (TCM) (if equipped)

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

High Speed Controller Area Network (HS-CAN) Communication Fault Chart:

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

CAN Module Commnication Message Chart (Part 1):

CAN Module Commnication Message Chart (Part 2):

CAN Module Commnication Message Chart (Part 3):

CAN Module Commnication Message Chart (Part 4):

CAN Module Commnication Message Chart (Part 5):