Filter
Top Products
41
MAF:
Mass Air Flow Sensor. This sensor mea-
sures the amount of air entering the engine
using a wire or film heated to a specific tem-
perature. Incoming air cools the wire. The
MAF sensor sends a frequency or voltage
signal (depending on sensor type) to the
PCM based on the voltage required to main-
tain that temperature. The signal frequency
or voltage increases when the mass of the
incoming air goes up. This gives the PCM
information required for control of fuel deliv-
ery and spark advance.
MAP:
Manifold Absolute Pressure Sensor. This
sensor measures manifold vacuum or pres-
sure and sends a frequency or voltage sig-
nal (depending on sensor type) to the PCM.
This gives the PCM information on engine
load for control of fuel delivery, spark ad-
vance, and EGR flow.
MAT:
Manifold Air Temperature sensor. A ther-
mistor a sensor whose resistance de-
creases with increases in temperature
is threaded into the intake manifold. It sends
a voltage signal to the PCM indicating the
temperature of the incoming air. The PCM
uses this signal for fuel delivery calculations.
MFI:
Multi-Port Fuel Injection. See MPFI.
MIL:
Malfunction Indicator Lamp. The MIL is also
known as a Check Engine Light or CEL.
Mode:
Refers to a type of operating condition, such
as idle mode or cruise mode.
MPFI:
Multi-Port Fuel Injection. MPFI is a fuel injec-
tion system using one (or more) injector(s)
for each cylinder. The injectors are mounted
in the intake manifold, and fired in groups
rather than individually.
NOx:
Oxides of Nitrogen. A pollutant. The EGR sys-
tem injects exhaust gases into the intake mani-
fold to reduce these gases at the tailpipe.
O2S:
This is an oxygen sensor that is threaded
into the exhaust system, directly in the
stream of exhaust gases. The PCM uses
the sensor to fine tune fuel delivery. The
sensor generates a voltage of 0.6 to 1.1 volts
when the exhaust gas is rich (low oxygen
content). The voltage changes to 0.4 volts or
less when the exhaust gas is lean (high
oxygen content). The sensor only operates
after it reaches a temperature of approxi-
mately 349°C (660°F).
ODM:
Output Device Monitor.
On-Board Diagnostics, Second Genera-
tion (OBD II):
With the passing of the 1990 Clean Air Act
Amendment, the EPA imposed more strin-
gent requirements. These requirements in-
clude the addition of multiple oxygen sen-
sors, one before the catalytic converter and
one after to provide the PCM with informa-
tion on catalyst efficiency and condition.
There are also computer-controlled EGR,
fuel pressure regulators, and smart ignition
systems.
OBD II requires a common data connector
and connector location. Further require-
ments include an industry-standard data
message, defined by both an industry com-
mittee of engineers from most major manu-
facturers and the SAE. Vehicle manufactur-
ers are required by law to provide at least a
minimum amount of data for emissions pro-
grams to access the critical emissions data
available through OBD II. OBD II began to
appear in vehicles in late 1994, and is sup-
posed to be equipment on all cars sold in
the US after January 1, 1996.
Open (Circuit):
A break in the continuity of a circuit such that
no current may flow through it.
Open Loop (O/L):
This is when the control system performs
an action (expecting a certain result), but
does not verify if the desired results were
achieved; i.e. the PCM operates a fuel injec-
tor expecting a certain amount of fuel to be