Actron GM Code Scanner CP9001 - Manual (Page 39)

39
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 idle speed
bypass air flow (see IAC).
The engine computer
sends the correct signals
to the motor for control.
TBI
Throttle Body Injection. A
fuel injection system
having one (or two)
injectors mounted in a
centrally located throttle
body, as opposed to
positioning the injectors
close to an intake valve
port.
TCC solenoid
Torque Convertor Clutch
solenoid. The ECM uses
this solenoid to control the
lock-up clutch in the
transmission torque
convertor. (When
activated, the lock-up
clutch directly connects the
engine to the
transmission.) During
warm engine cruise
conditions, the ECM
energizes this solenoid to
eliminate transmission
slippage and increase fuel
economy. The ECM
releases the lock-up action
when driving conditions
require the transmission to
operate as normal.
TDC
Top Dead Center. When a
piston is at its uppermost
position in the cylinder -
maximum compression.
Thermistor
A resistor whose
resistance changes with
temperature. Thermistors
are used as sensors for
vehicle coolant and
manifold air temperature.
The resistance decreases
as temperature goes up.
TPS
Throttle Position Sensor.
This is a rotary type
potentiometer connected
to the throttle shaft. It has
a voltage signal output
which increases as the the
throttle is opened. This
sensor is used by the ECM
for idle speed, spark
advance, fuel delivery,
emission system and
automatic transmission
(electronic type) control.
TTS
Transmission Temperature
sensor. This sensor is a
thermistor - a resistor
whose resistance
decreases as temperature
rises. It is mounted within
the transmission housing.
The ECM uses this sensor
to monitor transmission
operating temperature.
VSS
Vehicle Speed Sensor.
This sensor sends a
frequency signal to the
ECM. The frequency
increases as the vehicle
moves faster to give the
ECM vehicle speed
information.
WOT
Wide Open Throttle. The
vehicle operating condition
brought about when the
throttle is completely (or
nearly so) open. The ECM
will typically deliver extra
fuel to the engine at this
time for acceleration
purposes. The ECM uses
the Throttle Position
Sensor to identify the WOT
condition.