Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has 4 module communications networks:
- the standard corporate protocol (SCP) communications network (Navigator with navigation system only)
- the international standards organization (ISO) 9141 communications network
- the medium speed controller area network (CAN)
- the high speed CAN

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

Standard Corporate Protocol (SCP) Communications Network
The SCP communications network (Navigator with navigation system only) 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. The SCP communications network allows inter-module communication.

International Standards Organization (ISO) 9141 Communications Network
The ISO 9141 communications network is a single circuit communications network, circuit 70 (LB/WH). The restraint control module (RCM) and the parking aid module (Expedition only) are located on the ISO 9141 communication network. 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 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.

Medium Speed Controller Area Network (CAN)
The medium speed CAN has an unshielded twisted pair cable, data plus circuit 2180 (WH/BK) and data minus, circuit 2181 (BK/YE). The medium speed CAN is used for the air suspension control module, the climate controlled seat module, the driver seat module (DSM), the electronic automatic temperature control (EATC) module, the instrument cluster, the parking aid module (Navigator only), power liftgate module, and the vehicle security module communications. The medium speed 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.

High Speed Controller Area Network (CAN)
The high speed CAN has an unshielded twisted pair cable, data plus circuit 1814 (WH/LB) and data minus circuit 1815 (PK/LB). The high speed CAN is a high speed communications network used for the anti-lock brake system (ABS) module, the instrument cluster, the transmission control module (TCM) and the powertrain control module (PCM) communication. The high speed 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.