Communications Network: Notes

Fig 1: Locating Module Communications Network Components

Courtesy of FORD MOTOR CO.

The vehicle has two module communication networks: the standard corporate protocol (SCP) network, which is an unshielded twisted pair of wires (data bus plus, circuit 914 [T/O] and data bus minus, circuit 915 [PK/LB]), and the international standards organization (ISO) 9141 network which is a single wire (circuit 70 [LB/W]). Both networks can be connected to scan tool at one connector called the data link connector (DLC). This makes troubleshooting these systems easier by allowing one tester to be able to diagnose and control any module on the two networks from one connector. The DLC can be found under the instrument panel directly below the steering column.

The ISO 9141 network does not permit inter-module communication. When scan tool communicates to modules on the ISO 9141 network, scan tool must ask for all information; the modules cannot initiate communications.

The SCP 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 chassis ground or battery positive voltage (B+) or if some, but not all, termination resistors are lost.

Unlike the SCP, the ISO 9141 network will not function if the wire is shorted to chassis ground or battery positive voltage (B+). Also, if one of the modules on the ISO 9141 network loses power or shorts internally, communications to that module will fail. There are two modules on each network.