Data Link Communications Description and Operation

This vehicle is equipped with a computer system capable of performing multiple engine and body control functions. Vehicle components such as windows, locks, mirrors, etc. are controlled directly by their system control module. Each system control module communicates with other system control modules on a serial data circuit. The vehicle system control modules are all attached to the serial data circuit that provides the data link communications. This data link, or serial data circuit, provides 2-way communication between various engine and body control system control modules.

The control modules connected to the class 2 serial data circuit are listed below:

• Powertrain Control Module (PCM)
• Electronic Brake Control Module (EBCM)
• Electronic Suspension Control (ESC) Module*
• Body Control Module (BCM)
• Instrument Panel Cluster (IPC)
• Radio
• Sensing and Diagnostic Module (SDM)
• HVAC Control Assembly (HVAC) (with CJ2) *
• Driver Door Module (DDM)
• Passenger Door Module (PDM)
• Seat Control Module (SCM) *
• Remote Control Door Lock Receiver (RCDLR) *

* If equipped.

Some electrical system components are directly connected to and controlled by their system control module. Others systems accomplish the control functions by sharing data information with other system control modules on the serial data circuit to execute various vehicle functions. All system data information from sensors, switches, etc. can be monitored by any system module that is connected to the serial data circuit. Communications between each system control module is accomplished by sending a digitally coded message consisting of specific information. Communicating data information with other system control modules on the same serial data circuit, either input information or specific program information, provides more accurate and reliable computer system control functions.

All system control modules on the same serial data circuit use a communication process similar to a telephone system, where enormous amounts of information can be exchanged on a single data wire. The serial data circuit is used to communicate information between each system control module. Each system control module is assigned a specific recognition code, called a source ID. This code is used to identify which module is communicating on the serial data circuit. When a message is sent out on the serial data circuit, the recognition code will identify which particular module sent the message. These messages contain specific information, or commands, a system control module requires to function properly.

When a system receives a message it also "learns" the source ID of the system that sent it. This source ID is used to determine which system control module actually sent the message for State of Health (SOH) monitoring. SOH monitoring determines if a system control module is unable to communicate properly. Description and diagnosis of each system and control module is covered in the respective service manual section.