Communications Network
COMMUNICATIONS NETWORKModule Communications Network Components
- anti-lock brake system/traction control (ABS/TC) module or stability assist module
- restraint control module (RCM)
- vehicle security module
- powertrain control module (PCM)
- electronic automatic temperature control (EATC) module
- driver seat module (DSM)
- parking aid module
- four-wheel drive (4WD) control module
- instrument cluster
- tire pressure monitoring system module
- power liftgate module
- air suspension control module
- climate controlled seat modules (driver and passenger)
- navigation system module
PRINCIPLES OF OPERATION
The vehicle has 3 module communication networks:
- the standard corporate protocol (SCP) communications network
- the international standards organization (ISO) 9141 communications network
- the universal asynchronous receiver-transmitter (UART) based protocol (UBP) communications network
The diagnostic tool connects to all 3 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 3 networks from one connector. The DLC can be found under the instrument panel between the steering column and the radio.
The SCP communications 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 voltage, or if some but not all termination resistors are lost. The SCP communications network allows inter-module communication.
The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO 9141 communication network, the diagnostic tool must request all information, or initiate module commands.
The ISO 9141 communications network will not function if the wire 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 will fail.
The UBP communications network will not function if the wire is shorted to ground or voltage. The UBP is different from the ISO communication network in that it allows intermodule communication.
Anti-Lock Brake System (ABS) Module
The anti-lock brake system (ABS) module or stability assist module is on the SCP communication network. The ABS module or stability assist module controls the brake pressure to the four wheels to keep the vehicle under control while braking.
Restraints Control Module (RCM)
The restraint control module (RCM) is on the ISO 9141 network. The RCM controls the deployment of the air bags based on sensor input.
Vehicle Security Module
The vehicle security module is on the UBP communication network. The vehicle security module controls a variety of systems:
- windshield wipers
- warning chimes
- interior lamps
- exterior lamps
- power windows
- perimeter security
- remote keyless entry (RKE)/keyless entry
- lock functions
- monitors the entry doors and radio
Powertrain Control Module (PCM)
The powertrain control module (PCM) is on the SCP communication network. The PCM controls the engine for better fuel economy, emissions control, and failure mode detection and storage.
Electronic Automatic Temperature Control (EATC) Module
The electronic automatic temperature control (EATC) module is on the UBP communication network. The EATC module controls automatic climate functions that maintain the vehicle interior temperature at a constant setting.
Driver Seat Module
The driver seat module (DSM) is on the UBP communication network. The DSM controls the positioning and programming of the driver seat, pedals and both outside mirrors.
Parking Aid Module
The parking aid module is connected to the ISO communication network (Expedition only), and the UBP communication network (Navigator only). The module controls sensors in the rear bumper that detect close objects when the transmission is in REVERSE.
Four-Wheel Drive (4WD) Control Module
The four-wheel drive (4WD) control module is on the UBP communication network. The 4WD control module controls the four-wheel drive functions for the vehicle.
Instrument Cluster
The instrument cluster is on the SCP communication network. The instrument cluster also uses the UBP network to communicate with other modules on the UBP network. It is an analog face cluster with a digital odometer. The instrument cluster displays a variety of information.
Tire Pressure Monitoring System Module
The tire pressure monitoring system module is on the SCP communications network. The module and sensors monitor tire pressure and alert the driver when a concern may exist.
Power Liftgate Module
The power liftgate module is on the UBP network. The module controls the motor that opens and closes the liftgate.
Air Suspension Control Module
The air suspension control module is on the UBP 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.
Climate Controlled Seat Module
The driver and passenger climate controlled seat modules are on the UBP network. The climate controlled seat modules control the temperature of the driver and passenger seats.
Navigation System Module
The navigation module is on the SCP communications network (Navigator only). The navigation module controls the global positioning system on the vehicle.