Actron GM Code Scanner CP9001 User Manual
Page 38
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P/N
Park/Neutral switch. This
switch tells the ECM when
the gear shift lever is in the
Park or Neutral position.
Then the ECM will operate
the engine in an “idle”
mode.
Pressure Con-
trol solenoid
This solenoid is located
inside certain automatic
transmissions. The ECM
uses this solenoid to vary
the internal line pressure,
as required, based on
engine load condition
PROM
Programmable Read-Only
Memory. A small,
replaceable electrical
component hidden behind
an access door on the
ECM. The PROM contains
permanent programming
information the ECM needs
to operate a specific
vehicle model. Included
are vehicle weight, engine
and transmission type,
axle ratio and other
specifics.
PS
Power steering switch.
This tells the ECM when
power steering is being
used. The ECM can
prevent stalling on a small,
idling engine by watching
this switch and increasing
idle speed if power
steering is being used.
Purge solenoid
This device controls the
flow of fuel vapors from the
carbon canister to the
intake manifold. The
canister collects vapors
evaporating from the fuel
tank, preventing them from
escaping into the
atmosphere and causing
pollution. During warm
engine cruise conditions,
the ECM energizes the
Purge solenoid so the
trapped vapors are drawn
into the engine and
burned.
Quad Driver
An electrical device inside
the ECM. It functions as
four separate electronic
“switches” allowing the
ECM to energize relays or
solenoids.
Relay
A mechanical device for
switching high current
circuits on and off. It is
electronically controlled by
a low current circuit.
Relays allows a low power
ECM signal to control a
high power device such as
an electric cooling fan.
Reluctance
sensor
This sensor type consists
of a permanent magnet
with a coil of wire wrapped
around it. Nearby the
sensor is a toothed
“reluctor” ring made of iron
or steel. The ring is
attached around a rotating
component such as the
crankshaft. Whenever a
tooth from the ring passes
by the sensor, it attracts
the magnetic field lines
surrounding the magnet.
As the field lines move,
they pass through the wire
coil which generates a
small voltage pulse
(magnetic induction
principle). Thus, a voltage
pulse is generated every
time a tooth passes by the
sensor coil. The ECM
determines the speed of
rotation by measuring how
fast pulses appear.
Reluctance sensors may
be used for:
Crankshaft or Camshaft
–
speed, position (spark
timing or fuel injector
control).
Driveshaft
– vehicle speed
(transmission or torque
convertor control, cooling
fan use, variable assist
power steering and “cruise
control”).
Wheel Speed
– anti-lock
brake or traction control
systems.
Sensor
Device which give the ECM
information. The ECM can
only work with electrical
signals. The job of the
sensor is to take something
the ECM needs to know,
such as engine tempera-
ture, and convert it to an
electrical signal which the
ECM can understand. The
ECM uses sensors to
measure such things as
throttle position, coolant
temperature, engine speed,
incoming air and the like.
SFI or SEFI
Sequential Fuel Injection
or Sequential Electronic
Fuel Injection. A fuel
injection system using one
injector for each cylinder.
The injectors are mounted
in the intake manifold. The
injectors are fired
individually in the same
sequence as the spark
plug firing sequence.
Shift solenoid
Used in computer
controlled transmissions.
The solenoids (usually
two) are located in the
transmission housing and
are controlled by the ECM.
The ECM energizes the
solenoids individually, or in
combination, to select a
specific gear. (The
solenoids control the flow
of hydraulic fluid to the
transmission shifting
valves.) The ECM selects
the appropriate gear ratio
and shift point based upon
engine operating
conditions.
Short (circuit)
A fault condition: an
unwanted connection of
one electric circuit to
another causing a change
in the normal current flow
path.
Solenoid
A device to convert an
electrical signal to
mechanical motion. It
consists of a coil of wire
with a movable metal rod
in the center. When power
is applied to the coil, the
resulting electromagnetism
moves the rod and
performs some mechanical
action. The ECM often
uses solenoids to switch
vacuum lines on and off.
This allows the ECM to
control vacuum operated
devices such as an EGR
valve. Fuel injectors are
another type of solenoid.