Principles of Operation

PRINCIPLES OF OPERATION

The vehicle has 4 module communications networks:
- the standard corporate protocol (SCP) communications network (Navigator with navigation system only)
- the international standards organization (ISO) 9141 communications network
- the medium speed controller area network (CAN)
- the high speed CAN

The diagnostic tool connects to all 4 networks through the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one diagnostic tester to be able to diagnose and control any module on the 4 networks from one connector. The DLC can be found under the instrument panel between the steering column and the audio unit.

The SCP communications network (Navigator with navigation system only) remains operational even with the severing of one of the SCP communications network circuits. Communications also continue if one of the SCP communications network circuits are shorted to ground or voltage, or if some but not all termination resistors are lost. The SCP communications network allows inter-module communication.

The ISO 9141 communications network is a single circuit communications network, circuit 70 (LB/WH). The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO 9141 communications network, the diagnostic tool must request all information, or initiate module commands. The ISO 9141 communications network does not function if the circuit is shorted to ground or battery voltage. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module fail.

The high speed CAN has an unshielded twisted pair cable, data plus circuit 1814 (WH/LB) and data minus circuit 1815 (PK/LB). The high speed CAN is a high speed communications network used for the anti-lock brake system (ABS) module, the instrument cluster, the transmission control module (TCM) and the powertrain control module (PCM) communication. The high speed CAN remains operational even with the severing of one of the high speed CAN circuits. Communications also continues if one of the high speed CAN circuits are shorted to ground or voltage, or if some, but not all, termination resistors are lost.

The medium speed CAN has an unshielded twisted pair cable, data plus circuit 2180 (WH/BK) and data minus, circuit 2181 (BK/YE). The medium speed CAN is used for the air suspension control module, the climate controlled seat module, the driver seat module (DSM), the dual automatic temperature control (DATC) module, the instrument cluster, the parking aid module, power liftgate module, and the vehicle security module communications. The medium speed CAN remains operational even with the severing of one of the medium speed CAN circuits. Communications also continues if one of the medium speed CAN circuits are shorted to ground or voltage, or if some, but not all, termination resistors are lost.

Air Suspension Control Module
The air suspension control module uses the medium speed CAN. The air suspension control 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 on 4-wheel air suspension systems, or rear height sensors on the rear-wheel suspension systems. The module controls vehicle height adjustments by monitoring 2 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.

ABS Module
The ABS module uses the high speed CAN. The ABS module controls the brake pressure to the 4 wheels to keep the vehicle under control while braking.

Climate Controlled Seat Module
The climate controlled seat module uses the medium speed CAN. The climate controlled seat module control the temperature of the driver and passenger seats.

DSM
The DSM uses the medium speed CAN. The DSM controls the positioning and programming of the driver seat, pedals and both outside mirrors.

DATC Module
The DATC module uses the medium speed CAN. The DATC module controls automatic climate functions that maintain the vehicle interior temperature at a constant setting.

Instrument Cluster
The instrument cluster uses the medium speed CAN. The instrument cluster also uses the high speed CAN to communicate with other modules. It is an analog face cluster with a digital odometer. The instrument cluster displays a variety of information.

Navigation System Module
The navigation module is on the SCP communications network (Navigator only). The navigation system module controls the global positioning system on the vehicle.

Parking Aid Module
The parking aid module uses the ISO 9141 communications network (Expedition only), or the medium speed CAN (Navigator only). The module controls sensors in the rear bumper that detect close objects when the transmission is in REVERSE.

PCM
The PCM uses the high speed CAN. The PCM controls the engine for better fuel economy, emissions control, failure mode detection and storage. The PCM also controls 4x4 functionality.

Power Liftgate Module
The power liftgate module uses the medium speed CAN (Navigator only). The module controls the motor that opens and closes the liftgate. Restraints Control Module (RCM) The RCM uses the ISO 9141 communications network. The RCM controls the deployment of the air bags based on sensor input.

TCM
The TCM uses the high speed CAN (Navigator only). The TCM controls transaxle shifting, the electronic pressure control, and the torque converter clutch.

Vehicle Security Module
The vehicle security module uses the medium speed CAN. The vehicle security module controls a variety of systems:
- exterior lamps
- interior lamps
- lock functions
- monitors the entry doors and radio
- perimeter security
- power windows
- remote keyless entry (RKE)/keyless entry
- tire pressure monitoring system
- warning chimes
- windshield wipers