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M/T:
Manual transmission or manual transaxle.
MAF:
Mass Air Flow (sensor). Measures the amount and density of air entering the
engine and sends a frequency or voltage signal to the PCM. The PCM uses this
signal in its fuel delivery calculations.
MAP:
Manifold Absolute Pressure (sensor). Measures intake manifold vacuum or
pressure and sends a frequency or voltage signal (depending on sensor type)
to the PCM. This gives the PCM information on engine load for control of fuel
delivery, spark advance, and EGR flow.
MAT:
Manifold Air Temperature (sensor). A resistance sensor in the intake manifold
that sends a voltage signal to the PCM indicating the temperature of the
incoming air. The PCM uses this signal for fuel delivery calculations.
MIL:
Malfunction Indicator Lamp. The MIL is most commonly known as the Check
Engine or Service Engine Soon light. A required on-board indicator to alert the
driver of an emission-related malfunction.
Misfire:
Caused by the air fuel ratio being incorrect.
Monitor:
A test performed by the on-board computer to verify proper operation of
emission-related systems or components.
MPFI or MFI:
Multi-Port Fuel Injection. MPFI is a fuel injection 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. The system EGR and Camshafts injects exhaust gases into
the intake manifold to reduce these gases at the tailpipe.
O2S:
Oxygen 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). This sensor only operates after it
reaches a temperature of approximately 349ºC (660ºF). O2 sensors are usually
found both upstream and downstream of the catalytic converter. The PCM uses
these sensors to fine tune the air-fuel ratio and to monitor the efficiency of the
catalytic converter. See Bank 1, Bank 2, Sensor 1, Sensor 2.
OBD II:
On-Board Diagnostics, Second Generation. OBD II is a U.S.
Government-mandated standard requiring all cars and light trucks to have a
common data connector, connector location, communication protocol, DTCs
and code definitions. OBD II first appeared on vehicles in late 1994, and is
required to be present on all cars sold in the US after January 1, 1996.
ODM:
Output Device Monitor.