Actron GM Code Scanner CP9001 - Manual (Page 35)

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(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 measure-
ment.
ECM
Electronic Control Module.
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 ECM
receives information from
sensors, then energizes
various actuators to control
the engine. The ECM is
sometimes called PCM
(Powertrain Control
Module) in vehicles having
other computers. These
other computers are used
for climate control,
entertainment systems,
etc.
EFI
Electronic Fuel Injection. A
term applied to any system
where a computer controls
fuel delivery to an engine
by using fuel injectors.
EGR
Exhaust Gas Recirculation.
The EGR system
recirculates exhaust gases
back into the intake
manifold to reduce NO
x
emissions. The EGR valve
controls the flow of
exhaust gases back into
the intake manifold. Some
EGR valves are operated
with a vacuum signal while
others are electrically
controlled. The amount of
EGR valve opening
determines the flow
through the valve. EGR
recirculation is only used
during warm engine cruise
conditions. EGR flow at
other times can cause
stalling or no starts. There
are three types of EGR
systems controlled by the
ECM.
One system uses exhaust
backpressure to operate
the EGR valve. The ECM
does not control the EGR
valve in this case, but it
can switch off the valve
completely when desired.
(The ECM operates a
solenoid switch to cut off
the backpressure control
signal to the valve.)
The second system uses
an EGR valve entirely
controlled by the ECM.
This valve contains three
individual flow passages:
small flow, medium flow
and large flow. Each
passage has an electric
solenoid. (Passage closed
when solenoid off -
passage open when
solenoid energized.) The
ECM energizes one or
more solenoids in
combination to set up
different flow rates through
the valve as required.
The third system is also
directly controlled by the
ECM. This EGR valve is
vacuum operated (the
normally closed valve
opens as vacuum is
applied). The ECM applies
control vacuum to the EGR
valve using a solenoid
connected to a vacuum
source. The ECM uses a
duty cycle type signal to
vary the amount of vacuum
passing through the
solenoid. (See “Duty
Cycle” definition.)
EMI
Electromagnetic
Interference. Undesired
signals interfering with a
needed signal. For
example: static on a radio
brought about by lightning
flashes or closeness to
high voltage power lines.
ESC
Electronic Spark Control.
This is an ignition system
function which works on
vehicles having a knock
sensor mounted on the
engine block. The knock
sensor is wired to circuitry
in a separate module
(early version) or inside the
ECM (later version). If the
sensor detects engine
knock, the ESC function
alerts the ECM which will
immediately retard the
spark to eliminate the
knock condition.
EST
Electronic Spark Timing.
An ignition system where
the ECM controls the spark
advance timing. A signal
called EST goes from the
ECM to the ignition module
which fires the spark coil.
The ECM determines
optimum spark timing from
sensor information - engine
speed and RPM, throttle
position, coolant
temperature, engine load,
vehicle speed, Park/Neutral
switch position and knock
sensor condition.
EVO
Electronic Variable Orifice
actuator. This is a solenoid
mounted in the power
steering pump. It is used in
some variable assist power
steering systems. The
solenoid controls the
amount of fluid passed to
the steering gear.
Increasing fluid flow
generates more power
steering assist. The ECM
controls the solenoid by
using a duty cycle type
signal (see “duty cycle”
definition). The ECM uses
information from the
vehicle speed sensor
(VSS) and the handwheel
sensor (which sends a
signal related to the rate of
steering wheel turning).
During low speed turns, the
ECM increases the EVO
solenoid opening to provide
additional steering assist.
The ECM decreases
steering assist during
straight line driving by
reducing fluid flow through
the EVO solenoid.
EVRV
Electronic Vacuum
Regulator Valve. This
actuator is controlled by
the ECM and is used to
vary the amount of vacuum
applied to a vacuum
operated device - usually
the EGR valve.
FBC
Feedback Carburetor. This
is used on early versions of
computer controlled
engines. It is a carburetor
which can have its fuel