Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has 4 module communications networks:
- standard corporate protocol (SCP) communications network.
- international standards organization (ISO) 9141 communications network.
- universal asynchronous receiver-transmitter (UART)-based protocol (UBP) communications network.
- high speed controller area network (CAN).

The diagnostic tool connects to all 4 communications networks through the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one diagnostic tool to be able to diagnose and control any module on the 4 communications networks from one connector. The DLC is found under the instrument panel between the steering column and the radio.

Standard Corporate Protocol (SCP) Communications Network
The SCP communications network is an unshielded twisted pair cable, data plus circuit 4-EG7 (GY/RD) and data minus circuit 5-EG7 (BU/RD). The SCP communications network remains operational even with the severing of one of the SCP communications network circuits. Communications also continue if one of the SCP communications network circuits are shorted to ground or voltage, or if some but not all termination resistors are lost.

International Standards Organization (ISO) 9141 Communications Network
The ISO 9141 communications network uses a single circuit communications network circuit 4-EE10 (GY/BK). 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 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.

Universal Asynchronous Receiver-Transmitter (UART)-based Protocol (UBP) Communications Network
The UBP communications network uses a single circuit communications network circuit 4-ED6 (GY). 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.

High Speed Controller Area Network (CAN)
The high speed CAN is an unshielded twisted pair cable, data plus circuit 4-EC7 (GY/RD) and data minus circuit 5-EC7 (BU/RD). The high speed CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or the high speed CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If the high speed 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 high speed CAN bus may remain operational when 1 of the 2 termination resistors are not present. If there are issues with the high speed CAN, there may be missing functionality and problems connecting with a diagnostic tool. On the high speed 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.