Actuator:
A device that receives a voltage signal or com-
mand from a computer and responds by performing a me-
chanical action.
Air-Fuel Ratio:
The ratio of air to fuel by weight of the air
and fuel mixture drawn into the engine.
Airflow Sensor:
A sensor used to measure the rate, den-
sity, temperature, or volume of air entering the engine.
Air Gap:
The precise space between a pickup coil and trig-
ger wheel. The correct air gap is critical to proper opera-
tion of the sensor.
Ammeter:
An ammeter is an instrument used for measur-
ing the current flow in an electrical or electronic circuit.
Some ammeters are intended for use in direct current (DC)
circuits; others are designed for alternating current (AC) cir-
cuits.
Ampere:
The unit for measuring electrical current flow.
Analog Signal:
A voltage signal or processing action that
varies continuously with the variable being measured or
controlled.
Atmospheric Pressure:
Weight of air at sea level, about
14.7 pounds per square inch, decreasing at higher alti-
tudes.
Available Voltage:
The voltage present at a given point
within the electrical system.
Backpressure
: A pressure created by restrictions in the
exhaust system that tends to slow the exit of exhaust
gases from the combustion chamber.
Binary:
A mathematical system containing only two digits
(0 and 1), used by digital computers to process informa-
tion, make calculations, and develop output commands.
Boost Pressure:
The amount of air pressure increase
above atmospheric pressure provided by a turbocharger.
Breakout Box: (BOB)
A breakout box is a service tool that
tees-in between the computer and the multi-pin harness
connector. Once connected in series with the computer
and the harness, it permits measurements of computer
signals.
Carbon Dioxide (CO2):
A colorless, odorless, incom-
bustible gas formed as a byproduct of combustion in a
gasoline engine. Although not considered a pollutant, car-
bon dioxide percentage in the exhaust can be used to de-
termine combustion efficiency.
Carbon Monoxide (CO)
An odorless, colorless, tasteless,
poisonous gas. A major pollutant from an internal combus-
tion engine.
Catalyst:
Specific compounds that enhance a chemical
reaction without being consumed by the reaction.
Centrifugal Advance:
A method of advancing the ignition
spark using weights in the distributor that react to centrifu-
gal force generated by engine speed.
Check Valve:
A valve that permits flow in one direction but
prevents it in the opposite direction.
Circuit:
A circle or unbroken path of conductors com-
posed of wiring, switches, and other electrical components
that leads to and from a power source through the compo-
nent operated by the electric current.
Closed-Loop:
An operational mode in which the PCM
reads and responds to feedback signals from its sensors
and adjusts system operation accordingly.
Compression Pressure:
The total amount of air pressure
developed by a piston moving to TDC with both valves
closed.
Crankshaft Position Sensor (CKP):
An electronic device
designed to supply engine RPM and position to the PCM.
Data Link Connector (DLC):
A dedicated point for attach-
ing a scan tool to the vehicle communications network.
Data Parameter or Parameter Identifiers:
A measured
value of control system input or output operation. Parame-
ters include voltage signals, as well as temperature, pres-
sure, speed, and other data.
Detonation:
An unwanted explosion of an air-fuel mixture
caused by high heat and compression. Also called knock-
ing or spark knock.
Diagnostic Trouble Code (DTC):
A numeric or alphanu-
meric sequence relating directly to an abnormal signal from
a sensor in the onboard electronic system.
Dielectric Resistance:
A poor conductor of electrical cur-
rent or a high resistance.
Digital Multimeter:
A hand-held meter capable of meas-
uring voltage, resistance, and current flow then displaying
it in digital format on an LCD screen.
Digital Storage Oscilloscope (DSO):
A digital style oscil-
loscope with the ability to store data for review at a later
time.
Diode:
An electronic semiconductor device that acts as an
electrical gate to allow current in one direction but not the
other. Diodes are used to rectify alternating current pro-
duced by a generator into direct current.
Glossary
120
Summary of Contents for ASE-A8
Page 2: ......