Excursion 4WD V10-6.8L (2002)
Information Bus: Description and Operation
Principles and Operation
The vehicle has three module communication networks:
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Standard Corporate Protocol (SCP) communications network
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International Standards Organization (ISO) 9141 communications network
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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 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 Four-Wheel Anti-lock Brake System (4WABS) module is on the ISO 9141 communication network. The module controls brake pressure to the
Wheels to keep the vehicle under control while braking.
The 4-Wheel Drive (4WD) control module (if equipped) is on the ISO 9141 communication network. The 4WD control module controls the four wheel
drive functions for the vehicle.
The Restraint Control Module (RCM) control the deployment of the air bags based on sensor input. The RCM is on the ISO 9141 network. Refer to Air
Bag Systems.
The Overhead Trip Computer (OTC) is connected to the ISO 9141 communication network. The OTC computes and displays in metric or English:
average fuel economy, distance to empty, and compass heading. Refer to Instrument Panel, Gauges and Warning Indicators.
The parking aid module is connected to the ISO 9141 communication network. The module controls the sensors in the rear bumper that detect close
objects when the vehicle is in reverse. Refer to Collision Avoidance and Parking Assist Systems.
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.
The Auxiliary Powertrain Control Module (APCM) is on diesel engine equipped vehicles. The APCM is connected to the SCP communication network.
The APCM provides an operator interface to the drive-by-wire powertrain control system to affect charge protection, rpm control, and manual throttle
control between 1,300 and 2,500 rpm.
The Passive Anti-Theft System (PATS) module is connected on the SCP communication network. The PATS module enables or disables the PCM to
deter drive-away theft. Refer to Antitheft and Alarm Systems.
The instrument cluster is connected to the SCP communication network and the UBP communication network. The instrument cluster displays driver
information, including tachometer reading, fuel level, engine coolant level and speed. The message center is included in the high option level cluster and
displays door/hatch ajar information, lamp outage and low washer fluid level. Refer to Instrument Panel, Gauges and Warning Indicators.
The Driver Seat (DSM) Module (if equipped) is connected to the UBP communication network. The DSM controls the driver power seat. In addition,
the DSM is programmable to store seat position and pedal position. Refer to Seats.
The Electronic Automatic Temperature Control (EATC) module is connected to the UBP communication network. The EATC module controls
automatic climate functions that maintain the vehicle at a constant temperature setting. Refer to Heating and Air Conditioning.
The vehicle security module is on the UBP communication network. The vehicle security module controls a variety of systems:
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exterior lamps (RKE flashing and panic)
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RKE/keyless entry
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lock functions
