Information Bus: Description and Operation

The vehicle has two module communications networks. The Standard Corporate Protocol (SCP) which is an unshielded twisted pair cable (data bus plus, circuit 914 [T/O] and data bus minus, circuit 915 [P/LB]) and the International Standards Organization (ISO) 9141 network which is a single wire network (circuit 70 [LB/W]). Both networks can be connected to New Generation STAR (NGS) Tester at one connector called the Data Link Connector (DLC). This makes troubleshooting these systems easier by allowing one smart 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 between the steering column and the radio.

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

The SCP 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 battery positive voltage (B+) or a termination resistor is lost. This faulted condition is detected and reported to the host by the module's network bus interface circuits.

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

SCP Communication Network
The Powertrain Control Module (PCM) is on the SCP communication network. The PCM controls the engine for better fuel economy, emissions control and failure mode detection and storage.

ISO 9141 Communication Network
The ECS is on the ISO 9141 communication network. The ECS controls the deployment of the air bags based on sensor input.

The Generic Electronic Module (GEM)/Central Timer Module (CTM) is on the ISO 9141 communication network. The GEM is equipped on vehicles with four-wheel drive or vehicles with power windows. The CTM is equipped on vehicles with two-wheel drive or vehicles without power windows. The GEM controls a variety of systems:
^ 4x4.
^ Windshield wipers.
^ Courtesy lamps.
^ One touch down power windows, etc.
^ Warning chimes/lamps.

The Remote Anti-theft Personality (RAP) module is on the ISO 9141 communication network. The RAP module controls the anti-theft and keyless remote entry of the vehicle.

The 4-Wheel Anti-lock Brake System (4WABS) module is on the ISO 9141 communication network. The 4WABS module controls the brake pressure to the four wheels to keep the vehicle under control while braking.