Information Bus: Description and Operation

INFORMATION BUS and MODULE CONFIGURATION
The vehicle has two module communication networks. The Powertrain Control Module (PCM) is connected to the Standard Corporate Protocol (SCP), which is an unshielded twisted pair of wires Data Bus Plus, Circuit 914 (T/O) and Data Bus Minus, Circuit 915 (P/LB). The Air Bag Electronic Crash Sensor (ECS) module and any of the optional modules are connected to the ISO 9141 Link via a single wire Circuit 70 (LB/W]).

- The 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 ECS module is on the ISO 9141 Link network. The ECS controls the deployment of the air bags based on sensor input.

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

COMBINING MULTIPLE MODULE COMMUNICATIONS TO ONE ACCESS POINT
Both networks can be connected to the New Generation Star (NGS) Tester 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 Link network does not permit inter-module communication. When the NGS Tester communicates to modules on the ISO 9141 Link network, the NGS Tester must ask for all information; the modules cannot initiate communications.

FAULT TOLERANCE-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 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-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 ISO 9141 Link network loses power or shorts internally, communications to that module will fail.