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 single-wire network (Circuit 70 [LB/W]). Both networks can be connected to New Generation STAR (NGS) Tester through one connector called the Data Link Connector (DLC). This makes diagnosing these systems easier by allowing one smart tester to be able to diagnose and test 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 communications network does not permit inter module communication. When NGS Tester communicates to modules on the ISO 9141 communication network, 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. The PCM is the only module that contains termination resistors.

Unlike the SCP network, the ISO 9141 communication network will not function if the network 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 PCM is on the SCP communication network. The PCM controls the engine for better fuel economy, emissions control and failure mode detection and storage.

The Restraint Control Module (RCM) is on the ISO 9141 communication network. The RCM controls the deployment of the air bags based on sensor input.

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

The Generic Electronic Module (GEM) is on the ISO 9141 communication network. The GEM controls a variety of systems:
^ windshield wipers
^ courtesy lamps
^ 4-wheel shift on the fly
^ warning chimes
^ one touch down power windows

The remote anti-theft personality (RAP) module is on the ISO 9141 communication network. The RAP module controls the remote entry, interior lamp illumination signal to the GEM and panic alarm from the keyless entry remote.
The anti-lock brake control module is on the ISO 9141 communication network. The module controls brake pressure to the four wheels to keep the vehicle under control while braking.

The following describes the rear- and four-wheel air suspension modules:

The air suspension control module is on the ISO 9141 communication network and controls the air compressor motor (through a solid state relay) and all system solenoids. The module also provides power to front and rear height sensors. The module controls vehicle height adjustments by monitoring two height sensors, vehicle speed, a steering sensor, acceleration input, the door ajar signal, transfer case signals and the brake switch. The module also conducts all fail-safe and diagnostic strategies and contains self-test and communication software for testing the vehicle and module.

The control module is mounted in the passenger compartment inside the instrument panel above the radio and temperature controls.

The air suspension control module monitors and controls the system through a 32-pin two-way connector. It is keyed so that the control module cannot be plugged into an incorrect harness. There are two sides of the harness connection to the module. Each is uniquely colored and keyed to prevent reversal of connections.

The instrument cluster is on the SCP communication network. The instrument cluster is also called a Hybrid Electronic Cluster (HEC). It is an analog face cluster with a digital odometer. The instrument cluster displays a variety of information. The instrument cluster now includes the Passive Anti-theft System (PATS) software internally.