Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has 3 module communications networks:
- controller area network (CAN)
- international standards organization (ISO) 9141 communications network
- universal asynchronous receiver-transmitter (UART) based protocol (UBP) communications network

The diagnostic tool connects to the communications networks through the data link connector (DLC).

The DLC allows a diagnostic tool access to diagnose and test the vehicle systems of any module on the communications networks.

Controller Area Network (CAN)
The CAN has an unshielded twisted pair cable, data plus circuit 1908 (WH) and data minus circuit 1909 (BK). The CAN is a communications network used for the anti-lock brake system (ABS) module, the instrument cluster, powertrain control module (PCM) and the trailer brake controller communications.

The CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If CAN data minus is shorted to ground or an open exists on either bus line, module-to-module and module-to-tester communication is marginal at best. The CAN bus may remain operational when one of the two termination resistors are not present.

International Standards Organization (ISO) 9141 Communications Network
The ISO 9141 communications network is a single circuit communications network, circuit 70 (LB/WH). The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO 9141 communications network, the diagnostic tool must request all information or initiate module commands. The ISO 9141 communications network is a communications network used for the four-wheel drive (4WD) control module, the parking aid module and the restraint control module (RCM) communications. The ISO 9141 communications network does not function if the circuit is shorted to ground or voltage. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module fail.

Universal Asynchronous Receiver-Transmitter (UART) Based Protocol (UBP) Communications Network
The UBP communications network is a single circuit communications network, circuit 693 (OG). The UBP communications network is a communications network used for the electronic automatic temperature control (EATC) module, the instrument cluster and the vehicle security module communications. The UBP communications network does not function if the circuit is shorted to ground or voltage. The UBP communications network is different from the ISO 9141 communications network in that it allows intermodule communication.