OBD-II Acronyms 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. Here is a start on untangling these codes.

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