Principles of Operation

PRINCIPLES OF OPERATION

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

The CAN has an unshielded twisted pair cable, data plus, circuit 1827 (WH/LG) and data minus, circuit 1828 (PK/LG).

The UBP communications network uses a single circuit communications network circuit 1906 (VT), as does the ISO 9141 communications network, which is a single circuit communications network, circuit 70 (LB/WH).

All 3 communications networks are connected to the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing 1 diagnostic tool to be able to diagnose and control any module on the 3 communications networks from 1 connector. The DLC can be found under the instrument panel between the steering column and the audio unit.

Controller Area Network (CAN)
The CAN is an unshielded twisted pair cable, data plus circuit 1827 (WH/LG) and data minus circuit 1828 (PK/LG). The CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or the CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If the 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. If there are issues with the CAN, there may be missing functionality and problems connecting with a diagnostic tool. On the CAN, there are 2 terminating modules which are composed of the powertrain control module (PCM) and the instrument cluster which are located at the far opposite ends of the CAN wiring.

Universal Asynchronous Receiver Transmitter (UART)-based Protocol (UBP) Communications Network
The UBP communications network does not function if the circuit is shorted to ground or voltage. The UBP communications network allows inter-module communication. If one of the modules on the UBP communications network loses power or shorts internally, communications to that module fail.

International Standards Organization (ISO) 9141 Communications Network
The ISO 9141 communications network does not permit inter-module communication. When the diagnostic tool communicates to modules on the ISO 9141 communications network, the diagnostic tool must ask for all information; the modules cannot initiate communications.

The ISO 9141 communications network does not function if the circuit is shorted to ground or battery voltage. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module fail.