Equus 3173 - Import Code Reader - Manual (Page 12)

About Import Vehicle Diagnostic Systems
AUTOMOTIVE COMPUTER CONTROL SYSTEMS
9 Chapter 2
AUTOMOTIVE COMPUTER CONTROL SYSTEMS
The main purpose of the vehicle’s Computer Control System is
to provide maximum engine performance with the least
amount of air pollution and the best fuel efficiency possible.
The Computer Control System consists of the on-board
computer, and several related control devices (sensors,
switches, and actuators). Most on-board computers are located
inside the vehicle behind the dashboard, under the passenger’s
or driver’s seat, or behind the passenger side kick panel. Some
manufacturers may still position it in the engine compartment.
The sensors, switches, and actuators are devices such as
oxygen sensors, coolant temperature sensors, throttle position
sensors, fuel injectors, etc., that are located throughout the
engine, and are connected by electrical wiring to the on-board
computer.
The on-board computer is the heart of the Computer Control
System. The computer software contains several pre-
programmed reference values that represent the ideal air/fuel
mixture, spark timing, transmission gear selection, etc., for
any driving condition. These values are programmed at the
factory and are specific to each vehicle model.
The on-board computer receives information (inputs) from
sensors and switches located throughout the engine. These
devices monitor critical engine conditions (coolant
temperature, engine speed, engine load, throttle position,
air/fuel ratio, etc.). The computer compares the actual values
received from these sensors with the reference values that are
programmed in it’s memory. The computer commands the
necessary corrections through operating output actuators as
needed so that the incoming sensor values match the pre-
programmed reference values for that particular driving
condition.
Since vehicle operating conditions are constantly changing, the
computer continuously makes adjustments or corrections
(especially to the air/fuel mixture and spark timing) to keep all
the engine systems operating within the pre-programmed
reference values.