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 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)

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 data transfer speed of 125 Kbps for bus messages and is 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.

In the event that one of the 2 network circuits (MS-CAN + or MS-CAN -) becomes open to a module on the network, unreliable network communication to all modules on the network may result. The module to which the network circuit is open may repeatedly send network messages indicating there has been partial data received. This type of message is referred to as a negative-acknowledge (NACK) message. Repeated NACK messages may "load" the network with too much activity causing intermittent no communication to other network modules and/or the scan tool.

The following modules are on the MS-CAN:
- Smart junction box (SJB)
- Instrument cluster (IC)
- Audio control module (ACM)
- Audio digital signal processing (DSP) module (if equipped)
- Satellite digital audio receiver system (SDARS) module (if equipped)
- Power running board (PRB) module (if equipped)
- Parking aid module (PAM) (if equipped)
- Liftgate/trunk module (LTM) (if equipped)
- Heating ventilation air conditioning (HVAC) module - electronic manual temperature control (EMTC) (if equipped)
- Heating ventilation air conditioning (HVAC) module - electronic automatic temperature control (EATC) (if equipped)
- Driver seat module (DSM) (if equipped)
- Dual climate control seat module (DCSM) (if equipped)
- Audio rear control unit (RCU) (if equipped)
- Rear entertainment module (RETM) (if equipped)

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 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.

In the event that one of the 2 network circuits (HS-CAN + or HS-CAN -) becomes open to a module on the network, unreliable network communication to all modules on the network may result. The module to which the network circuit is open may repeatedly send network messages indicating there has been partial data received. This type of message is referred to as a negative-acknowledge (NACK) message. Repeated NACK messages may "load" the network with too much activity causing intermittent no communication to other network modules and/or the scan tool.

The following modules are on the HS-CAN:
- PCM
- ABS module
- Restraints control module (RCM)
- IC
- Transmission control module (TCM)
- 4X4 control module (if equipped)
- Air suspension module (if equipped)

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

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 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):