Principles 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 and data bus minus, circuit 915 ) and the International Standards Organization (ISO) 9141 communications network, which is a single-wire network (circuit 70 [/WH]). Both networks can be connected to the scan tool through one connector called the Data Link Connector (DLC). The DLC can be found under the instrument panel between the steering column and the radio.

The SCP communication network allows inter-module communication. This allows single inputs or outputs to be shared by multiple modules over common circuits.

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 power, or if some, but not all, termination resistors are lost. The PCM is the only module that contains termination resistors.

The ISO 9141 communications network does not permit inter-module communication. When the scan tool communicates to modules on the ISO 9141 communication network, the scan tool initiates all communications.

Unlike the SCP network, the ISO 9141 communication network will not function if the network is shorted to ground or power. 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. This module also performs all Passive Anti-theft System (PATS) functions. For additional PCM information, refer to Powertrain Management. For PATS information, refer to Antitheft and Alarm Systems.

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. For additional information, refer to Air Bag Systems.

The Electronic Automatic Temperature Control (EATC) module is on the SCP communication network. The EATC module controls automatic climate functions that maintain the vehicle interior temperature at a constant setting. For additional information, refer to Heating and Air Conditioning.

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

For additional GEM information, refer to Multifunction Electronic Control Module.

The Driver Seat Module (DSM) is on the ISO 9141 communication network. The DSM controls the positioning and programming of the driver seat, pedals and both outside mirrors. For additional information, refer to Seats.

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. For additional information, refer to Keyless Entry.

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. For additional information, refer to Antilock Brake System.

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 on four-wheel air suspension systems, or rear height sensors on the rear-wheel suspension systems. 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.

For additional information on the rear-wheel air suspension, refer to Electronic Level Control. For additional information on the four-wheel air suspension, refer to Electronic Level Control.

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. For additional information, refer to Instrument Panel, Gauges and Warning Indicators.

The Parking Aid Module (PAM) is connected to the ISO 9141 communication module. The module controls sensors in the rear bumper that detect close objects when the vehicle is in reverse. For additional information, refer to Collision Avoidance and Parking Assist Systems.