Principles of Operation: Notes

WARNING: This page is about a different car, the 2005 Lincoln Navigator and 2005 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

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.

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.

The ISO 9141 communications network is a single circuit communications network, circuit 70 (LB/WH). 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.

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 remains operational even with the severing of one of the high speed CAN circuits. Communications also continues if one of the high speed CAN circuits are shorted to ground or voltage, or if some, but not all, termination resistors are lost.

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 dual automatic temperature control (DATC) module, the instrument cluster, the parking aid module, power liftgate module, and the vehicle security module communications. The medium speed CAN remains operational even with the severing of one of the medium speed CAN circuits. Communications also continues if one of the medium speed CAN circuits are shorted to ground or voltage, or if some, but not all, termination resistors are lost.