Principles of Operation: Notes

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

The vehicle has three module communication networks protocols:

Controller area network (CAN)
Standard corporate protocol (SCP) communication network
International standards organization (ISO) 9141

The CAN has an unshielded twisted pair cable, data bus plus circuit 1827 (WH/LG) and data bus minus circuit 1828 (PK/LG). The ISO 9141 communications network, which is a single wire network (circuit 70 [LB/WH]), and the standard corporate protocol (SCP), which is an unshielded twisted pair cable, data bus plus, circuit 915 (PK/LB) and data bus minus circuit 914 (TN/OG). 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 radio.

The CAN communications network is a high speed communication network used for diagnostic communication. The CAN communication network will operate in a degraded mode with the severing of one of the bus wires. Communications will also operate in a degraded mode 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 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.