OTC Tools Code Scanner Manual Del Usuario página 58

Crankshaft Position
Sensor. This crankshaft
mounted sensor sends a
frequency signal to the
ECA. (See PIP signal
definition.) It is used to
reference fuel injector
operation and synchronize
spark plug firing on
distributorless ignitions.
Clutch switch.
A diagnostic Self-Test only
used on Sequential
Electronic Fuel Injector
(SEFI) engines. The test
turns each injector on and
off to check if they are
closed or damaged.
Data Communication Link.
A two wire circuit used by
the ECA to exchange
information with other
computer controlled
modules.
An electronic signal which
has only two (2) voltage
values: a "low" value (close
to zero) and a "high" value
(usually 5 volts or greater).
Sometimes the low voltage
condition is called "Off" and
the high voltage condition
is called "On". Signals
which can have any
voltage value are called
"analog" signals.
Distributorless Ignition
System. In general use,
this refers to a system
which produces the ignition
spark without the use of a
distributor. Ford technical
manuals use DIS when
referring to a particular
distributorless ignition
system where the ECA
directly controls timing of
spark firing. (Compare to
EDIS definition.)
A transistor "switch" inside
the ECA used to apply
power to an external
device. This allows the
ECA to control relays,
solenoids and small
motors.
A term applied to frequency
signals – those which are
constantly switching
between a small voltage
value (close to zero) and a
larger value (usually 5 volts
or greater). Duty cycle is
the percentage of time the
signal has a large voltage
value. For example, if the
signal is "high" (large
voltage) half of the time
then the duty cycle is 50%.
If the signal is "high" only
one fourth of the time, then
the duty cycle is 25%. A
duty cycle of 0% means the
signal is always at a "low"
value and not changing. A
duty cycle of 100% means
the signal is always at a
"high" value and not
changing. The engine
control computer uses duty
cycle type signals when it
wants more than just "on-
off" control of an actuator.
This is how it works: A 50%
duty cycle signal going to a
vacuum switching solenoid
means the solenoid will be
"on" (passing full vacuum)
half the time and "off"
(passing no vacuum) half
the time. The average
amount of vacuum passing
through the solenoid will be
one half of the full value
because the solenoid is
only "on" for one half of the
time. (The signal switches
at a rapid rate, such as ten
times a second.) Thus, the
computer can get a
vacuum controlled actuator
to move half way between
"no vacuum" position and
"full vacuum" position.
Other positions can be
achieved by changing the
duty cycle of the control
signal which in turn
changes the average
amount of control vacuum.
Digital Volt Meter. An instru-
ment using a numeric read-
out to display measured
voltage values as opposed
to a moving needle on a
gauge face. Usually the
instrument has other mea-
suring capabilities, such as
resistance and current, and
may be called a DMM
(Digital Multi-Meter). Most
DVM's have 10 Megohm
input impedance. This means
58
the circuit under test will not
be electronically disturbed
when the DVM is connected
for a measurement.
A user action expected by
the ECA during the course
of a diagnostic Self-Test.
Normally, this means
performing a brief wide-
open-throttle action during
the Engine Running Self-
Test. The ECA sends a
single voltage pulse through
the STO circuit (making a
blink on the Code Scanner
LED) signaling the user to
perform the Dynamic
Response action.
Electronic Control
Assembly. The "brains" of
the engine control system. It
is a computer housed in a
metal box with a number of
sensors and actuators
connected with a wiring
harness. Its job is to control
fuel delivery, idle speed,
spark advance timing and
emission systems. The ECA
receives information from
sensors, then energizes
various actuators to control
the engine. Sometimes
vehicles have additional
computers controlling other
functions. These include
anti-lock brake and active
suspension systems.
Engine Coolant Temperature
sensor. This sensor is a
thermistor – a resistor whose
resistance decreases with
increases in temperature.
The sensor is threaded into
the engine block and
contacts the engine coolant.
The ECA uses this signal for
control of fuel delivery, spark
advance, EGR flow and
other emission control devices.
Electro-Drive Fan relay.
The ECA energizes this
relay to apply power to the
Electro-Drive Fan (mounted
in front
of the radiator) for engine
cooling purposes. The fan
is only turned on when the
ECA determines cooling is
necessary.