Principles of Operation: Notes

WARNING: This page is about a different car, the 2004 Lincoln Navigator and 2004 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

The vehicle has 3 module communication networks:

The standard corporate protocol (SCP) communications network
The international standards organization (ISO) 9141 communications network
The universal asynchronous receiver-transmitter (UART) based protocol (UBP) communications network

The diagnostic tool connects to all 3 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 3 networks from one connector. The DLC can be found under the instrument panel between the steering column and the radio.

The SCP communications network 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 SCP communications network allows inter-module communication.

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 request all information, or initiate module commands.

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 UBP communications network will not function if the wire is shorted to ground or voltage. The UBP is different from the ISO communication network in that it allows intermodule communication.