Principles of Operation

PRINCIPLES OF OPERATION

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

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 either communications networks from one common connector. The DLC can be found under the instrument panel between the steering column and the driver door.

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.

On the SCP communications network there are 3 terminating modules, which are the driver door module (DDM), the lighting control module (LCM), and the instrument cluster.

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 inter-module communications. 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 open. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module fail. The ISO 9141 communications network is used to communicate with the restraint control module (RCM) and the fire suppression module (FSM).

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.

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. 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 the anti-lock brake system (ABS) module and the instrument cluster, which are located at the far opposite ends of the CAN wiring.