Principles of Operation

WARNING: This page is about a different car, the 2003 Lincoln Navigator and 2003 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

The vehicle has three module communication networks:

the standard corporate protocol (SCP) communications network
the international standards organization (ISO) 9141 communications network
the UART based protocol (UBP) communications network

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

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 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 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.

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. For additional information, refer to REMOVAL & INSTALLATION - BLACKWOOD, EXPEDITION, F150 PICKUP & NAVIGATOR - GASOLINE .

The restraint control module (RCM) is on the ISO 9141 network. The RCM controls the deployment of the air bags based on sensor input. For additional information, refer to AIR BAG RESTRAINT SYSTEMS .

The tire pressure monitoring module is on the SCP communications network. The module and sensors monitor tire pressure and alert the driver when a concern may exist. For additional information, refer to INFORMATION AND MESSAGE CENTER .

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. For additional information, refer to CLIMATE CONTROL SYSTEM-GENERAL INFORMATION .

The driver and passenger temperature-controlled seat modules are on the UBP network. The temperature controlled seat modules control the temperature of the driver and passenger seats. For additional information, refer to SEATING .

The vehicle security module is on the UBP communication network. The vehicle security module controls a variety of systems:

windshield wipers
courtesy lamps
warning chimes
interior lamps
exterior lamps
power windows
perimeter security
RKE/keyless entry
lock functions
monitors the entry doors and radio

Refer to MULTIFUNCTION ELECTRONIC 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. Refer to SEATING .

The 4-wheel anti-lock brake/traction control (ABS/TC) module or stability assist module (if equipped) is on the ISO 9141 and the SCP communication network. The ABS/TC module or stability assist module (if equipped) controls the brake pressure to the four wheels to keep the vehicle under control while braking. Refer to ANTI-LOCK CONTROL .

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.

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 air suspension information, refer to VEHICLE DYNAMIC .

The instrument cluster is on the SCP and UBP communication network. It is an analog face cluster with a digital odometer. The instrument cluster displays a variety of information. For additional information, refer to INSTRUMENT CLUSTER .

The parking aid module is connected to the UBP communication module. The module controls sensors in the rear bumper that detect close objects when the vehicle is in reverse. Refer to PARKING AID .

The 4-wheel drive (4WD) control module is on the UBP communication network. The 4WD control module controls the four wheel drive functions for the vehicle. Refer to FOUR WHEEL DRIVE SYSTEMS .

The power liftgate module is on the UBP network. The module controls the motor that opens and closes the liftgate. Refer to BODY CLOSURES .