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OBD Acronyms and Jargon

A listing of OnBoardDiagnostics abbreviations and terms.

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.


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


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