63
Self-Test
Connector
The connector that the
Code Scanner plugs into
for testing purposes. The
connector is wired to the
ECA, and is located in the
engine compartment. Tests
are run and codes are read
with the Code Scanner
connected. Sometimes this
connector is called VIP
(Vehicle in Process).
Self-Test Input
(STI)
A wire between the ECA
and either the Self-Test
connector (MCU systems)
or a separate connector
(EEC-IV systems). The
wire is used to activate the
Self-Test procedures. The
Code Scanner connects
STI to vehicle ground when
the Test/Hold switch is in
the TEST position and
disconnects STI when the
Test/Hold switch is in the
HOLD position.
Self-Test
Output (STO)
A wire between the ECA
and the Self-Test
connector. Results of
vehicle diagnostic tests are
sent along this circuit by
using a voltage pulse
signal. The signal switches
between “High” (+5 volts)
and “Low” (close to zero
volts). The Code Scanner
light is OFF when STO is
“High” and ON when STO
is “Low”. Note: the light
may be on or off when the
ignition key is off – depends
upon vehicle. The flashes
represent code numbers
used to locate problems.
Sensor
Device which give the ECA
information. The ECA can
only work with electrical
signals. The job of the
sensor is to
take something the ECA
needs to know, such as
engine temperature, and
convert it to an electrical
signal which the ECA can
understand. The ECA uses
sensors to measure such
things as throttle position,
coolant temperature,
engine speed, incoming air,
etc.
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.
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
elec- trical current 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 ECA often uses
solenoids to switch vacuum
lines on and off. This allows
the ECA to control vacuum
operated devices such as
an EGR valve. Fuel
injectors are another type
of solenoid.
Spark Retard
Solenoid
Used on MCU systems
having a knock sensor. The
MCU module energizes this
solenoid during engine
knock conditions. The
solenoid bleeds vacuum
from the distributor
advance to retard spark
timing.
SPOUT
Spark Output signal from
the ECA. Sent to TFI-IV or
DIS ignition modules to fire
the ignition coil(s) and
create spark voltage.
SS1
Shift Solenoid #1. Located
in certain electronically
controlled transmissions
along with Shift Solenoid
#2. The ECA energizes
these solenoids (one or
both) to engage the desired
transmission gear.
Stepper Motor
A special type of electric
motor with a shaft that
rotates in small “steps”
instead of a continuous
motion. A certain sequence
of frequency type signals is
required to step the motor
shaft. A different signal
sequence will step the shaft
in the opposite direction.
No signals keeps the shaft
still in position. A constant
signal drive will
continuously rotate the
shaft. The shaft is usually
connected to a threaded
assembly which moves
back and forth to control
things such as throttle
position. The engine
computer sends the correct
signals to the motor for
control.
STI
Self-Test Input. (See Self-
Test Input definition.)
STO
Self-Test Output. (See Self-
Test Output definition.)
TAB
Thermactor Air Bypass
solenoid. (Sometimes
called AM-1.) The ECA
energizes this solenoid to
apply vacuum (and thus
activate) the TAB valve.
Normally, this valve allows
incoming air to pass into
the rest of the system.
When activated, the valve
takes the incoming air and
dumps it back into the
atmosphere. Refer to
Thermactor Air System
description for more details.
TAD
Thermactor Air Diverter
solenoid. (Sometimes
called AM-2.) The ECA
energizes this solenoid to
apply vacuum (and thus
activate) the TAD valve.
Normally, this valve directs
incoming air to the catalytic
converter. When activated,
the valve takes the
incoming air and and
directs it to the exhaust
manifold. Refer to
Thermactor Air System
description for more details.
TDC
Top Dead Center. When a
piston is at its uppermost
position in the cylinder –
maximum compression.
