Like any government instigated project, OBD-II quickly became a mouse's nest of acronyms, jargon, shorthand and code phrases that have meaning to the select few and sometimes seem to serve to keep the rest of us at bay.

Here is a start on untangling these codes. Send in your additions to the list as you run across them. If you run across acronyms or jargon you don't understand, send them in and we'll try to decipher them for you.

AFC - Air Flow Control

ALDL - Assembly Line Diagnostic Link. Former name for GM (only) Data Link Connector, the connector socket into which the scan tool plug is inserted; sometimes used to refer to any pre-OBD II computer signals

CAN - Controller Area Network

CARB - California Air Resources Board

CFI - Central Fuel Injection (a.k.a. Throttle Body Fuel Injection TBI)

CFI - Continuous Fuel Injection

CO - Carbon Monoxide

DLC - Data Link Connector

Driving Cycle - A specific sequence of start-up, warm-up and driving tasks that tests all OBD II functions (Details)

DTC - Diagnostic Trouble Code

ECM - Engine Control Module- usually the main in-car computer controlling emissions and engine operation

ECT - Engine Coolant Temperature

EEC - Electronic Engine Control

EEPROM or E²PROM - Electrically Erasable Programmable Read Only Memory

EFI - Electronic Fuel Injection

EGR -  Exhaust Gas Recirculation

EMR - Electronic Module Retard

EPA - Environmental Protection Agency. Federal agency. Office of Mobile Sources is the branch concerned with auto emissions.

ESC - Electronic Spark Control

EST - Electronic Spark Timing

DPFE - Differential Pressure Feedback EGR sensor ( On Ford OBDII systems).

DTC - Diagnostic Trouble Code

FLI - Fuel Level Indicator

Fuel Trim - Engine computer function that keeps the air/fuel mixture as close to the ideal 14.7:1 stoichiometric ratio as possible

HC - Hydrocarbons

HEI - High Energy Ignition

HO₂S - Heated Oxygen Sensor

IAT - Intake Air Temperature

ISO 9141 - International Standards Organization OBDII communication mode, used by Chrysler and most foreign cars. One of three hardware layers defined by OBD II

J1850PWM - (Pulse Width Modulated) SAE-established OBD II communication standard used by Ford domestic cars and light trucks. One of three hardware layers defined by OBD II

J1850VPW - (Variable Pulse Width Modulated) SAE-established OBD II communication standard used by GM cars and light trucks. One of three hardware layers defined by OBD II

J1962 - SAE-established standard for the connector plug layout used for all OBD II scan tools

J1978 - SAE-established standard for OBD II scan tools

J1979 - SAE-established standard for diagnostic test modes

J2012 - SAE-established standard accepted by EPA as the standard test report language for emission tests

MAF - Mass Air Flow

MAP - Manifold Absolute Pressure

MAT - Manifold Air Temperature

MFG - Manufacturer

MIL - Malfunction Indicator Light. The "Check Engine Light" on your dash.

NOx - Oxides of Nitrogen

O₂ - Oxygen

OBD - On-Board Diagnostics

OBDII or OBD II - Updated On-Board Diagnostics standard effective in cars sold in the US after 1-1-96

Parameters - Readings on scan tools representing functions measured by OBD II and proprietary readings

PCM - Powertrain Control Module, the on-board computer that controls engine and drive train

PCV - Positive Crankcase Ventilation

PID - Parameter ID

Proprietary Readings - Parameters shown by on-board computers which are not required by OBD II, but included by manufacturer to assist in trouble-shooting specific vehicles.

PTC - Pending Trouble Code

RPM - Revolutions Per Minute

SAE - Society of Automotive Engineers, professional organization that set the standards that EPA adopted for OBD and OBD II

Scan Tool - Computer based read-out equipment to display OBD II parameters

SES - Service Engine Soon dash light, now referred to as MIL

SFI - Sequential Fuel Injection

Stoichiometric ( Stoy'-kee-o-metric) Ratio - Theoretical perfect combustion ratio of 1 part gas to 14.7 parts air

TBI - Throttle Body Injection

TPI - Tuned Port Injection

TPS - Throttle Position Sensor

VAC - Vacuum

VCM - Vehicle Control Module, the in-car computer that oversees engine management, transmission operation, anti-lock brakes, and other functions not directly related to emissions control

VIN - Vehicle Identification Number

VSS - Vehicle Speed Sensor

WOT - Wide Open Throttle