Note. The smart junction box (SJB) is also known as the Generic Electronic Module (GEM).
Vehicle communication utilizes both the medium and high speed Controller Area Network (CAN) communications. CAN is used for many modules to communicate with each other on a common network. CAN in-vehicle networking, is a method for transferring data among distributed electronic modules via a serial data bus. Without serial networking, intermodule communication requires dedicated, point to point wiring resulting in bulky, expensive, complex, and difficult to install wiring harnesses. Applying a serial data network reduces the number of wires combining the signals on a single network. Information is sent to the individual control modules that control each function.
The vehicle has 2 module communication networks
- Medium Speed (MS) CAN
- High Speed (HS) CAN
Both networks are connected to the Data Link Connector (DLC). This makes diagnosis and testing of these systems easier by allowing one scan tool to be able to diagnose and control any module on both networks from one connector. The DLC can be found under the instrument panel between the steering column and the Audio Control Module (ACM).
Scheme 1
| Module Name | Network Type | Termination Module |
|---|---|---|
| Accessory Protocol Interface Module (APIM) (if equipped) | HS-CAN MS-CAN | No No |
| Audio control module (ACM) | MS-CAN | No |
| Audio Digital Signal Processing (DSP) module (if equipped) | MS-CAN | No |
| ABS module | HS-CAN | No |
| Driver seat module (DSM) (if equipped) | MS-CAN | No |
| Dual Climate Control Seat Module (DCSM) (if equipped) | MS-CAN | No |
| 4X4 control module (if equipped) | HS-CAN | No |
| Headlamp Control Module (HCM) (if equipped) | HS-CAN | No |
| HVAC module (if equipped) | MS-CAN | No |
| Instrument cluster (IC) (gateway module) | HS-CAN MS-CAN | Yes Yes |
| Liftgate/trunk module (LTM) (if equipped) | MS-CAN | No |
| Occupant classification system module (OCSM) | HS-CAN | No |
| Parking aid module (PAM) (if equipped) | MS-CAN | No |
| PCM | HS-CAN | Yes |
| Rear entertainment module (RETM) (if equipped) | MS-CAN | No |
| Restraints control module (RCM) | HS-CAN | No |
| Satellite digital audio receiver system (SDARS) module (if equipped) | MS-CAN | No |
| Smart junction box (SJB) | MS-CAN | Yes |
| Steering angle sensor module (SASM) (if equipped) | HS-CAN | No |
MS-CAN Operation
The MS-CAN communicates using bussed messages. The MS-CAN has an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows sharing of information between all modules on the network.
The MS-CAN is a medium speed communication network used for the following modules
- ACM
- APIM
- DCSM (if equipped)
- DSM (if equipped)
- DSP module (if equipped)
- HVAC module (if equipped)
- IC
- LTM (if equipped)
- PAM (if equipped)
- RETM (if equipped)
- SDARS module (if equipped)
- SJB
HS-CAN Operation
The HS-CAN communicates using bussed messages. The HS-CAN uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows sharing of information between all modules on the network.
The HS-CAN is a high speed communication network used for the following modules
- ABS module
- HCM (if equipped)
- IC
- OCSM
- PCM
- RCM
- SASM (if equipped)
- 4X4 control module (if equipped)
Principles of Operation
Note. The smart junction box (SJB) is also known as the generic electronic module (GEM).
Vehicle communication utilizes both the 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
- High speed (HS) CAN
- Medium speed (MS) CAN
HS-CAN and 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
See also:
• SUPPLEMENTAL RESTRAINT SYSTEM
• SEATING