Information Bus: Description and Operation

The vehicle has two module communications networks.

The Powertrain Control Module (PCM) is connected with unshielded twisted pair cable (Data Bus Plus, circuit 914 [T/O] and Data Bus Minus, circuit 915 [P/LB]), using the Standard Corporate Protocol (SCP) which allows two or more signals being sent over one circuit.

The Integrated Air Bag Module (IABM) and any of the optional modules are connected to the ISO 9141 Link via a single wire (circuit 70 [LB/W]). Both networks can be connected to the New Generation STAR (NGS) tester or other compatible scan tool 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 diagnostic communication network does not permit inter-module communication. When the NGS communicates to modules on the diagnostic communication network, the NGS must ask for all information; the modules cannot initiate communications.

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

Fault Tolerance of the Diagnostic Communications Network
Unlike the SCP, the ISO 9141 Link will not function if the wire is shorted to chassis ground or battery positive voltage (B+). Also, if one of the modules on the diagnostic communication network loses power or shorts internally, communications to that module will fail.

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

The Integrated Air Bag Module (IABM) is on the diagnostic communication network. The IABM controls the deployment of the air bags based on sensor input.

The Generic Electronic Module (GEM) is on the diagnostic communication network. The GEM controls a variety of systems:

- Windshield wipers.
- Courtesy lamps.
- 4-wheel shift on the fly.
- One touch down power windows, etc.

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

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