Principles of Operation

PRINCIPLES OF OPERATION

NOTE: The smart junction box (SJB) is also known as the generic electronic module (GEM).

Vehicle communication utilizes both medium and high speed controller area network (CAN) communications. CAN is a method for transferring data among distributed electronic modules using a serial data bus.

The vehicle is equipped with 2 module communication networks:
- Medium speed (MS) CAN
- High speed (HS) CAN

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 MS-CAN may remain operational with only one termination resistor present.

The following modules are on the MS-CAN:
- Accessory protocol interface module (APIM) (if equipped)
- Audio control module (ACM)
- Audio digital signal processing (DSP) module (if equipped)
- Driver door module (DDM) (if equipped)
- Driver seat module (DSM) (if equipped)
- Dual climate control seat module (DCSM) (if equipped)
- Heating ventilation air conditioning (HVAC) module (if equipped)
- Instrument cluster (IC)
- Parking aid module (PAM) (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:

MS-CAN Communication Fault Chart:

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 HS-CAN may remain operational with only one termination resistor present.

The following modules are on the HS-CAN:
- 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)
- 4X4 control module (if equipped)

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

HS-CAN Communication Fault Chart:

CAN Module Communication Message Chart (Part 1):

CAN Module Communication Message Chart (Part 2):

CAN Module Communication Message Chart (Part 3):

CAN Module Communication Message Chart (Part 4):

CAN Module Communication Message Chart (Part 5):

CAN Module Communication Message Chart (Part 6):