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Hall Effect Sensor:
This sensor is a three wire-type of sensor
containing electronic circuitry. Two wires
supply power and ground, while a third
wire carries the sensor signal back to the
PCM. The sensor consists of a perma-
nent magnet and a small module con-
taining a transistorized Hall Effect switch.
A small air gap separates the sensor and
the magnet. The magnetic field causes
the Hall switch to turn on and send out a
low voltage signal. If a metal strip (iron or
steel) is placed in the gap, it will block the
magnetic field from reaching the Hall de-
vice. This causes the Hall switch to turn off
and send a high voltage signal out on the
signal wire.
The metal strips (blades) are part of a cup
or disk attached to a rotating component
such as the crankshaft or camshaft. As
the blades pass through the sensor gap,
the signal voltage will switch high and low,
creating a series of pulses. The PCM de-
termines the speed of rotation by mea-
suring how fast pulses appear. Hall Effect
type sensors may be used to measure
speed and position of the crankshaft or
camshaft for spark timing and fuel in-
jector control.
HO2S
Heated Oxygen Sensor.
IAC:
Idle Air Control. This is a device mounted
on the throttle body which adjusts the
amount of air bypassing a closed throttle
so that the PCM can control idle speed.
The IAC moves a pintle within the air by-
pass passage. When the PCM wants to
change idle speed, it will move the pintle
backwards for more air and a fast idle, or
forward for less air and a slower idle.
ICM:
Ignition Control Module.
I/M:
Inspection and Maintenance.
Inputs:
Electrical signals running into the PCM.
These signals come from sensors, switches
or other electronic modules. They give the
PCM information about vehicle operation.
ISC:
Idle Speed Control. This refers to a small
electric motor mounted on the throttle body
and controlled by the PCM. The ISC motor
moves a spindle back and forth. When the
throttle is released during idle, it rests on
this spindle. The PCM can control idle speed
by adjusting this spindle position. The PCM
determines the desired idle speed by look-
ing at battery voltage, coolant temperature,
engine load, and RPM.
Knock Sensor (KS):
This sensor is used to detect engine deto-
nation or knock. When spark knock occurs,
the sensor emits a pulsing signal. Depend-
ing on the vehicle, this signal either goes to
the PCM or a separate ESC (Electronic Spark
Control) module. Then the spark advance is
retarded until detonation stops. The sensor
contains a piezoelectric element and is
threaded into the engine block. Vibrating the
element generates the signal pulse. Spe-
cial construction makes the element sensi-
tive only to engine vibrations associated with
detonation knocking.
Knock:
See Detonation.
KOEO:
Key On, Engine Off.
KOER:
Key On, Engine Running.
LCD:
Liquid Crystal Display.
LT:
Long Term fuel trim.
M/T:
Manual transmission or manual transaxle.