OTC Tools Code Scanner Manual Del Usuario página 52

E C A
BRAINS OF THE
COMPUTER
(oil pressure, fuel level, etc.)
Signals running into the computer
are referred to as "inputs."
Sensors monitor such things as:
• Engine temperature
• Intake manifold vacuum
• Throttle position
• RPM
• Incoming air (temperature, amount)
• Exhaust gas oxygen content
• EG R Valve flow
Mo st engine computer system s will use
the sensor types listed above.
Additional sensors may be used
depending upon the engine, vehicle
type or other tasks the computer must
do. Note that information from one
sensor may be used by the computer
for many different tasks. For example,
engine temperature is something the
computer needs to know when
controlling fuel delivery, spark timing,
idle speed and emission syst ems. The
sensor information may be very
important for one engine control
function, but only used to "fine tune" a
second one.
• Thermistor – This is a resistor whose
resistance changes with temperature.
It is used to measure temperatures of
coolant or incoming air. It has two
wires connected to it.
• Potentiometer – This signals a
position, such as throttle position or
EG R valve position. It connects to
three wires: one for power, one for
ground and one to carry the position
signal back to the computer.
• Switches – These are either ON
(voltage signal to the computer) or
OFF (no voltage signal to the
computer). Switches connect to two
wires and tell the computer simple
things, such as whether or not the air
conditioner is running.
• Signal Generator – These create
their own signal to tell the computer of
some condition, such as exhaust
gas oxy gen content, camshaft
position, or intake manifold
vacuum. They may have one , two
or three wires connected to them.
The computer can only send out
electrical signals (referred to as
"outputs"). Devices called actuators are
powered by the computer to control
things. Actuator types include:
• Solenoids – These are used to control
a vacuum signal, bleed air, control fuel
flow, etc.
• Relays – These switch high amperage
power devices on and off, such as
electric fuel pumps or electric cooling fan s.
• Motors – Small motors are often used
to control idle speed.
Not all of the computer outgoing signals
go to actuators. Sometimes information is
sent to electronic modules, such as
ignition or trip computer.
Operation and emiss ion performance
depend upon precise fuel control. Early
computer controlled vehicles used
ele ctronically adjustable carburetors, but
fuel injectors were soon introduced.
The job of the computer is to provide the
optimum mixture of air and fuel (air/fuel
ratio) to the engine for best performance
under all operating conditions.
The computer needs to know:
• ...what the engine operating condition
is. Sensors us ed: coolan t te mperature,
throttle position, ma nif old absolute
pressure, mass air flow, RPM.
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