Information Bus: Description and Operation

The vehicle has two module communication 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 [PK/LB]) and the International Standards Organization (ISO) 9141 communications network, which is a single wire network (circuit 70 [LB/W]). Both networks can be connected to New Generation STAR (NGS) Tester by 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 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 battery positive voltage (B+), or if some, but not all, termination resistors are lost.

Unlike the SCP network, 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.

The Rear Air Suspension Module (RASM) is connected to the SCP communication network. The RASM controls the vehicle's air ride suspension and the variable assist steering function.

The anti-lock brake control module is connected to the SCP communication network. The module controls the brake pressure to the four wheels to keep the vehicle under control while braking.

The Audio Control Module (ACM) is connected to the SCP communication network and also to the Audio Control Protocol II (ACP II) communication network. The ACM communicates with the compact disc and the cellular phone transceiver.

The Driver Door Module (DDM) is connected to the SCP communication network. The module controls many functions including power windows, power locks, and keyless remote entry. The DDM also communicates with the Driver Seat Module (DSM) to control power seat and mirror memory.

The DSM is connected to the SCP communication network. The DSM controls the driver power seat. The module also communicates with the DDM to control the driver seat memory and both outside memory mirror functions.

The Electronic Automatic Temperature Control (EATC) module is connected to the SCP communication network. The EATC module controls automatic climate functions that maintain the vehicle at a constant temperature setting.

The Electronic Crash Sensor (ECS) module is connected to the ISO 9141 communication network. The ECS module controls the deployment of the air bags based on sensor input.

The Hybrid Electronic Cluster (HEC) is connected to the SCP communication network. The REC displays information received on the SCP including speedometer, odometer, fuel, and message center warnings. The HEC also controls the Passive Anti-theft System (PATS).

The Lighting Control Module (LCM) is connected to the SCP communication network. The LCM controls both interior and exterior lighting, anti-theft functions and warning chimes.

The Next Generation Speed Control (NGSC) servo is connected to the SCP communication network. The servo, when activated, controls and maintains vehicle speed by actuating the throttle linkage.

The Powertrain Control Module (PCM) is connected to the SCP communication network. The PCM controls the engine performance, electronic ignition, emission controls and on board diagnostics.