Principles of Operation: Notes

WARNING: This page is about a different car, the 2006 Mercury Milan, 2006 Lincoln Zephyr, and 2006 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

The vehicle has 2 module communications networks:

High speed controller area network (CAN)
Medium speed 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.

Both 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.

High Speed Controller Area Network (CAN)

The high speed CAN is an unshielded twisted pair cable using data plus circuit VDB04 (WH/BU) and data minus circuit VDB05 (WH). The high speed CAN is not designed to operate under single point fault conditions. If either circuit is shorted to voltage or the high speed CAN data plus is shorted to ground, module-to-module and module-to-tester communication is not possible. If the high speed 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.

There are 2 terminating modules on the high speed CAN, which are the powertrain control module (PCM) and the instrument cluster located at the far opposite ends of the high speed CAN wiring. The high speed CAN bus may remain operational when one of the two termination resistors are not present. If there are issues with the high speed CAN, there may be missing functionality and problems connecting with a diagnostic tool.

The termination resistors are internal components to the module. If a module's termination resistance is found to be the cause of the high speed CAN network fault, a new module must be installed.