Information Bus: Description and Operation

Communications Network

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

Multiplexing is a method of sending 2 or more signals simultaneously over a single circuit. Multiplexing is used to allow 2 or more electronic modules (nodes) to communicate simultaneously over a twisted-wire pair [data (+) and data (-)] network. The information or messages that can be communicated on these wires consists of commands, status or data. The advantage of using multiplexing is to reduce the weight of the vehicle by reducing the number of redundant components and electrical wiring.

The vehicle has 2 module communication networks which are connected to the Data Link Connector (DLC), located under the instrument panel:

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

The HS-CAN and MS-CAN are defined by various ISO documents:

- ISO 11898 specifies the electrical, mechanical, and procedural interface for Controller Area Network (CAN) serial communication technology.
- ISO 15765 specifies network-layer protocol and timing parameters for CAN-based systems.
- ISO 14229 specifies a common set of unified diagnostics and changes the way PIDs, DTCs and active commands are processed and displayed on the scan tool.

Network Topology









Medium Speed Controller Area Network (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
- Audio DSP module (Navigator only)
- Audio RCU (if equipped)
- DCSM (if equipped)
- DSM (if equipped)
- HVAC module
- IC
- LTM (if equipped)
- PAM (if equipped)
- PRB (if equipped)
- SDARS module (if equipped)
- SJB
- RETM (if equipped)

High Speed Controller Area Network (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:

- 4X4 control module (if equipped)
- ABS module
- APIM
- IC
- PCM
- RCM
- TCM
- VDM (if equipped)

Network Termination

The CAN uses a network termination circuit to improve communication reliability. The network termination of the CAN bus takes place inside the termination modules by termination resistors. Termination modules are located at either end of the bus network. As network messages are broadcast in the form of voltage signals, the network voltage signals are stabilized by the termination resistors. Each termination module has a 120 ohm resistor across the positive and negative bus connection in the termination module. With 2 termination modules on each network, and the 120 ohm resistors located in a parallel circuit configuration, the total network impedance, or total resistance is 60 ohms.

Network termination improves bus message reliability by:

- stabilizing bus voltage.
- eliminating electrical interference.