This document is an attempt to corral some of the alphabet soup that accompanies automotive terminology, in particular, terms that we are likely to encounter while working on fuel saving projects. If you run across an acronym that should be included here, be sure to write me at email@example.com. If you can't find it here, then check in AutoZone's extensive online Automotive Terms Glossary.
AFS: Air/Fuel Ratio Sensor. Also spelled "A/FS".
DTC: Diagnostic Trouble Code. The code number that the ECU gives you to help diagnose an error condition. For 1996 and newer vehicles, these can be read by standard OBD-II readers. Older vehicles may have a system for initiating a blink code, whereby the error numbers are read by the number of blinks of the Check Engine Light.
EOP: Engine Oil Pressure sensor.
HEGO: Heated Exhaust Gas Oxygen sensor. Another name for an oxygen sensor.
MAP: Manifold Absolute Pressure sensor. Measures the pressure inside the intake manifold. The ECU compares this to the barometric pressure sensor (outside air pressure) to determine the difference between the pressure in the manifold and the outside air.
MAT: Manifold Air Temperature.
MIL: Malfunction Indicator Light. Same as CEL (Check Engine Light). See above.
MMW: Milliliters per Minute per Watt. This is a unit of measure of how efficient a cell is at making hydrogen. It doesn't tell us the total output of a cell. But it does tell us how much HHO is being made per watt of energy expended to make it. It starts out with LPM or liters per minute, which is the usual way HHO output is measured. It multiplies this by 1,000, which converts Liters to Milliliters. Then it divides that number by the number of watts (watts = volts times amps). The result is MMW, or Milliliters per Minute per Watt.
O2S: Oxygen Sensor.
OBD-II: On Board Diagnostic system. Prior to 1996 the systems varied by manufacturer. Jan 1, 1996 marked the beginning of a mandated standard for all new vehicles to conform to. This was ODB-II. Now the same reader can plug into any car and read it's information, including engine sensor readings, trouble codes, etc. For more information see this page.
PCV: Positive Crankcase Ventilation. Also PCV valve. See wiki for more information.
PWM: Pulse Width Modulator. OK, fine. But what the heck is a pulse width modulator? For more information, please see What is a PWM?
Stoichiometric ( Stoy'-kee-o-metric) Ratio - Not an acronym, I know. But it comes up a lot and I don't have another good place for it. This is the theoretical perfect combustion ratio of 1 part fuel to 14.7 parts air.
VCM: Vehicle Control Module. Yet another name for the ECU. Aren't acronyms fun?
VSS: Vehicle Speed Sensor.
WOT: Wide Open Throttle sensor.