Focus L4-2.0L DOHC VIN 3 (2002)
Information Bus: Description and Operation
Principles and Operation
The vehicle has two module communication networks:
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The Standard Corporate Protocol (SCP) communications network.
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The international standards organization (ISO) 9141 communications network.
The diagnostic tool connects to the two 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 inter-module 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 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 air bag control module controls the deployment of the air bags based on sensor input. The air bag control module is on the ISO 9141 network.
The Anti-lock Brake System (ABS) module is connected to the SCP communication network. The module controls the brake pressure to the four wheels
to keep the vehicle under control while braking.
The instrument cluster is connected to the SCP communication network. The instrument cluster displays driver information, including tachometer
reading, fuel level, engine coolant level and speed.
The Generic Electronic (GEM) module is on the ISO 9141 communications network. The GEM controls a variety of systems:
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Windshield wipers
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Courtesy lamps
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Warning chimes
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Interior lamps
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Exterior lamps
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Power windows
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Security
For additional GEM information, REFER to Multifunction Electronic Control Module (General Module).
