Principles of Operation: Notes

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

The vehicle has 3 module communication networks:

medium speed controller area network (CAN)
high speed controller area network (CAN)
international standards organization (ISO) 9141

The medium speed CAN has an unshielded twisted pair cable, data bus plus circuit 1827 (WH/LG) and data bus minus, circuit 1828 (PK/LG). The high speed CAN also has an unshielded twisted pair cable, data bus plus circuit 1847 (WH/OG) and data bus minus, circuit 1848 (PK/OG). The ISO 9141 communications network, which is a single wire network, circuit 70 (LB/WH). All three networks are connected to 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 three networks from one connector. The DLC can be found under the instrument panel between the steering column and the audio unit.

The high speed CAN is a high speed communication network used for instrument cluster, powertrain control module (PCM) and anti-lock brake system (ABS) module communication. The medium speed CAN is used for smart junction box (SJB) and electronic automatic temperature control (EATC) module communications. The CAN will remain operational even with the severing of one of the bus wires. Communications will also continue if one of the bus wires is shorted to ground or voltage, or if some but not all termination resistors are lost.

The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO 9141 communication network, the diagnostic tool must ask for all information; the modules cannot initiate communications. The ISO 9141 communications network will not function if the wire 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 will fail. The ISO communication network is used to communicate with the restraints control module (RCM).