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Neutral Drive Switch. Used
on vehicles with automatic
transmissions. The ECA
uses this switch to
determine when the
transmission is in or out of
gear. The ECA can adjust
idle speed to compensate
for increased engine
loading due to engaged
transmission.
Neutral Gear Switch. Used
on vehicles with manual
transmissions. The ECA
uses this switch to
determine when the
transmission is in or out of
gear.
Neutral Pressure Switch.
Located in automatic
transaxle. The ECA uses
this switch to determine
when the transaxle is in or
out of gear.
Overdrive Cancel Switch.
Used by vehicle operator.
Signals ECA to prevent
shifting transmission into
overdrive (4th gear)
regardless of operating
conditions.
Overdrive Cancel Indicator
Light. Located in
passenger compartment.
Light turns on when vehicle
operator uses Overdrive
Cancel Switch to disable
4th gear transmission
operation.
A break in the continuity of
a circuit such that no
electrical current can flow.
This is when a control
system performs an action
(expecting a certain result),
but has no way of verifying
if the desired results were
achieved. Example: The
ECA pulses a fuel injector
expecting a certain amount
of fuel to be delivered. (The
ECA assumes everything
in the fuel system is
operating as expected.) In
open loop operation, the
ECA has no way of
checking the actual amount
of fuel delivered. Thus, a
faulty injector or incorrect
fuel pressure can change
the amount of fuel delivered
and the ECA would not
know it.
Electrical signals sent from
the ECA. These signals
may activate relays or
other actuators for control
purposes around the
vehicle. The signals can
also send information from
the ECA to other electronic
modules, such as ignition
or trip computer.
Pressure Feedback EGR
sensor. The ECA uses this
sensor to determine the
amount EGR flow. The task
is involved. In this EGR
system, a small opening
separates the exhaust
manifold from the EGR
valve input. All the gases
flowing through the EGR
valve must first pass
through this opening.
Scientific principles allow
the ECA to calculate EGR
flow providing it can
determine the pressure on
both sides of this opening
(that is, both the EGR valve
input side and the manifold
side). The PFE sensor
measures the pressure
seen at the EGR side. The
sensor sends a voltage
signal which increases as
pressure is increased. The
manifold side pressure must
be calculated by the ECA
based on RPM, exhaust
system characteristics and
other information. The ECA
can then finally calculate
EGR flow. Note that with
this system, the PFE signal
is NOT a direct measure of
EGR flow!
Profile Ignition Pick-Up
signal. It is a frequency
type, providing crankshaft
position and speed
information. The ECA uses
PIP as a reference to
create properly timed
ignition system and fuel
injector signals. The PIP
signal comes from a sensor
mounted in the distributor
(TFI-IV ignitions) or from a
separate crankshaft
mounted sensor
(Crankshaft Position
Sensor) used on
distributorless ignitions.
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Power Steering Pressure
Switch. This tells the ECA
when power steering is
being used. The ECA can
prevent stalling on a small,
idling engine by watching
this switch and increasing
idle speed if power steering
is being used.
Another name for Self-Test.
(See Self-Test definition.)
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
ECA signal to control a
high power device such as
an electric cooling fan.
Read-Only Memory. This is
inside the ECA. The ROM
contains permanent
programming information
the ECA needs to operate
a specific vehicle model.
Included are vehicle
weight, engine and
transmission type, axle
ratio and other specifics.
Spark Advance Word.
A signal used in some
Distributorless Ignition
Systems. Sent from the
ECA to the DIS ignition
module to control spark
advance timing. The SAW
signal is a series of voltage
pulses. The width of the
pulses is what tells the DIS
module what timing is
desired – wider pulses
mean less spark advance.
An extra-wide pulse puts
the DIS module
in a "repetitive spark" mode
where several sparks are
generated for every
cylinder firing (used on
some vehicles at idle for
lower emissions and
smoother performance).
Sometimes called "Quick
Test". A series of tests
built-into the ECA which
help locate vehicle
problems.
The Code Scanner is used
to perform the tests and get
the results (in the form of
code numbers).
Hide quick links:
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