Information Bus: Description and Operation

The vehicle has two module communications networks. The Powertrain Control Module (PCM) is connected to the Standard Corporate Protocol (SCP) link. The Integrated Air Bag Module (IABM) and any of the optional modules are connected to the ISO 9141 Link via a single wire. 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 diagnostic communication network does not permit inter-module communication. When NGS Tester communicates to modules on the diagnostic communication network, NGS Tester must ask for all information; the modules cannot initiate communications.

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 IABM is on the diagnostic communication network. The IABM controls the deployment of the air bags based on sensor input.

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

The Passive Anti-Theft System (PATS) module is on the multiplex communication network. The PATS module contains circuitry to connect the vehicle electrical system, the transceiver module, the vehicle module communications network and the vehicle theft indicator located in the instrument cluster. The PATS module uses a microprocessor to control the system functions. The PATS module microprocessor stores the ignition key codes in non-volatile memory. The PATS module can be diagnosed through the DLC.

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

A microcontroller-based electronic module 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 of 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 system 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.