Information Bus: Description and Operation

The module communications network consists of the following:
^ Powertrain Control Module (PCM).
^ Integrated Air Bag Diagnostic Monitor (IABM).
^ Passive Anti-Theft System (PATS) Module.
^ Generic Electronic Module (GEM).
^ Remote Anti-Theft Personality (RAP) Module.
^ Rear Air Suspension (RAS) Module/4-Wheel Air Suspension (4WAS).
^ 4-Wheel Anti-Lock Brake System (4WABS) Module.

The vehicle has two module communications networks. The Powertrain Control Module (PCM) is connected to 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]). 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 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 tester communicates to modules on the diagnostic communication network, the NGS tester must ask for all information; the modules cannot initiate communications.

Fault Tolerance Of The SCP
The Standard Corporate Protocol (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 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 Of The Diagnostic Communications Network
Unlike the Standard Corporate Protocol (SCP), the ISO 9141 Link will not function if the wire is shorted to 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 air bag diagnostic monitor is on the diagnostic communication network. The air bag diagnostic monitor 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.
^ Warning chimes.
^ One touch down power windows.

The Remote Anti-Theft Personality (RAP) is on the diagnostic communication network. The RAP module controls the remote entry, interior lamps, 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 the 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 data link connector.

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.