Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has 3 module communications network protocols:
- controller area network (CAN)
- standard corporate protocol (SCP) communications network
- international standards organization (ISO) 9141 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.

All 3 communications networks are connected to the 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 3 communications networks from one common connector. The DLC can be found under the instrument panel between the steering column and the driver door.

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 may be awake when the key is in the OFF position to carry out functions such as accessory delay. In order to do diagnostics, it is necessary to have the key in the ON position.

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. If there are issues with the CAN, there may be missing functionality and problems connecting with a diagnostic tool.

Standard Corporate Protocol (SCP) Communications Network
The SCP communications network is an unshielded twisted pair cable, data plus circuit 914 (TN/OG) and data minus circuit 915 (PK/LB). The SCP communications network remains operational even with the severing of one of the SCP communications network circuits. If one of the bus wires become shorted to ground or voltage, or if some but not all termination resistors are lost, communications can continue at a degraded level. The SCP communications network allows inter-module communication.

International Standards Organization (ISO) 9141 Communications Network
The ISO 9141 communication network is a single circuit communications network, circuit 70 (LB/WH). 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, voltage or a open. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module fails.