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CTS

See Coolant Temperature
Sensor or Coolant Temperature
Switch.

Cylinder Head

Temperature

Sensor

The Cylinder Head
Temperature sensor is mounted
in the cylinder head usually
near the thermostat.
Temperature is usually
measured by a thermistor - a
resistor whose resistance
changes with temperature. The
hotter the sensor gets, the
lower the resistance becomes.

Detonation

Sensor (KNK)

The ECU uses this device to
detect engine detonation
(knocking). When spark knock
occurs, the sensor sends a
pulsing signal. The ECU than
retards spark advance until no
detonation is sensed. The
sensor contains a piezoelectric
element and is threaded into
the engine block. Vibrating the
element generates the signal.
Special construction makes the
element only sensitive to the
engine vibrations associated
with knocking.

Digital Signal

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.

Digital Volt Meter

(DVM)

An instrument using a numeric
readout to display measured
voltage values as opposed to a
moving needle on a gauge face.
Usually the instrument has other
measuring 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 the circuit under test will
not be electronically disturbed
when the DVM is connected for
a measurement.

Direct Ignition

System (DIS)

DIS uses 1 ignition coil per spark
plug. The coil is mounted directly
to the spark plug (sometimes
called a “coil per plug” system).
No distributor or spark plug wires
are used. Power to the coils is
switched by the ECU or an
ignition module. Information from
various sensors is required to
fire the proper coil at the correct
time. The system needs to know
crankshaft and camshaft position
and speed, engine temperature,
loading, throttle position and
RPM.

DIS

See Direct Ignition System or
Distributorless Ignition System.

Distributor

A mechanical device used to
switch the high voltage,
generated by the ignition coil, to
the proper spark plug.

Distributorless

Ignition system

(DIS)

This system uses one ignition
coil for each pair of cylinders.
The cylinders are paired such
that one is on the compression
stroke while the other is on the
exhaust stroke. When the coil is
powered, spark plugs in both
cylinders fire at the same time.
The spark in the exhaust
cylinder has no effect. (Which is
why this method is sometimes
called a “Wasted Spark” ignition
system.) No distributor is used.
Power to the coils is switched
by the ECU or an ignition
module. Information from
various sensors is required to
fire the proper coil at the correct
time. The system needs to
know crankshaft and camshaft
position and speed, engine
temperature, loading, throttle
position and RPM.

Driver

A transistor “switch” inside the
ECU used to apply power to an
external device. This allows the
ECU to control relays,
solenoids and small motors.

Duty Cycle

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.