Knowledgebase: General
OBD-II Acronyms and Jargon
Posted by Alex (Im) E. on 31 January 2013 09:15 PM

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

ECU - Engine Control Unit

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



A/C: air conditioning


AC: air cleaner

AIR: secondary air injection

A/T: automatic transmission or transaxle

B+: battery positive voltage

BARO: barometric pressure

BCM: body control module

CAC: charge air cooler

CFI: continuous fuel injection

CL: closed loop

CKP: crankshaft position sensor

CKP REF: crankshaft reference

CMP: camshaft position sensor

CMP REF: camshaft reference

CO: carbon monoxide

CO2: carbon dioxide

CPP: clutch pedal position

CTOX: continuous trap oxidizer

CTP: closed throttle position

DEPS: digital engine position sensor

DFCO: decel fuel cut-off mode

DFI: direct fuel injection

DIC: driver information center

DLC: data link connector

DTC: diagnostic trouble code

DTM: diagnostic test mode

EBCM: electronic brake control module

EBTCM: electronic brake traction control module

EC: engine control

ECM: engine control module

ECL: engine coolant level

ECT: engine coolant temperature

EEPROM: elecrically erasable programmable read only memory

EFE: early fuel evaporation

EGR: exhaust gas recirculation

EGRT: EGR temperature

EI: electronic ignition

EPROM: erasable programmable read only memory

EVAP: evaporative emission system

FC: fan control FF: flexible fuel

FP: fuel pump

FT: fuel trim

FTP: federal test procedure

GCM: governor control module

GEN: generator (alternator)

GND: ground

H20: water

HO2S: heated oxygen sensor

HO2S1: upstream heated oxygen sensor

HO2S2: up or downstream heated oxygen sensor

HO2S3: downstream heated oxygen sensor

HC: hydocarbon

HVAC: heating ventilation and air conditioning system

IA: intake air

IAC: idle air control

IAT: intake air temperature

IC: ignition control circuit

ICM: ignition control module

IFS: inertia fuel shutoff

I/M: inspection/maintenance

I/M 240: inspection/maintenance 240 emissions test

IPC: instrument panel cluster

ISC: idle speed control

KOEC: key on, engine cranking

KOEO: key on, engine off

KOER: key on, engine running

KS: knock sensor

KSM: knock sensor module

LEV: low emission vehicle

LT: long term fuel trim

MAF: mass airflow sensor

MAP: manifold absolute pressure sensor

MC: mixture control

MDP: manifold differential pressure

MFI: multiport fuel injection

MIL: malfunction indicator lamp

MPH: miles per hour

NOX: oxides of nitrogen

O2S: oxygen sensor

OBD: onboard diagnostics

OBD I: onboard diagnostics generation one

OBD II: onboard diagnostics, second generation

OC: oxidation catalyst

ODM: output device monitor

OL: open loop

OSC: oxygen sensor storage

PAIR: pulsed secondary air injection

PCM: powertrain control module

PCV: positive crankcase ventilation

PNP: park/neutral switch

PROM: program read only memory

PSA: pressure switch assembly

PSP: power steering pressure

RAM: random access memory

RM: relay module

ROM: read only memory

RPM: revolutions per minute (engine speed)

SC: supecharger

SCB: supercharger bypass (wastegate)

SDM: sensing diagnostic mode

SFI: sequential fuel injection

SRI: service reminder indicator

SRT: system readiness test

ST: short term fuel trim

TB: throttle body

TBI: throttle body injection

TC: turbocharger

TCC: torque converter clutch

TCM: transmission or transaxle control module

TFP: throttle fluid pressure

TP: throttle position

TPS: throttle position sensor

TVV: thermal vacuum valve

TWC: three way catalyst

TWC+OC: three way + oxidation catalytic converter

ULEV: ultra low emission vehicle

VAF: volume airflow

VCM: vehicle control module

VR: voltage regulator

VS: vehicle sensor

VSS: vehicle speed sensor

WU-TWC: warm up three way catalytic converter

WOT: wide open throttle

ZEV: zero emission vehicle



Baud Rate: The speed at which bits of computer data are transmitted through the serial data stream or on the controller area network (CAN) bus.

Bus: Another name for the basic circuit that carries data between all the modules in a vehicle. Also refered to as the Controller Area Network (CAN) bus.

CAN: Controller Area Network, the bus circuit over which all the modules in the vehicle communicate with each other. Communication faults over the bus can cause unpredictable driveability problems and will set special fault codes.

Closed Loop: An operating mode of the fuel feedback control system where the powertrain control module uses the rich/lean signal from the oxygen sensor to control the fuel mixture. Closed loop usually does not occur until the oxygen sensor is hot to produce a signal, and the engine has reached a certain temperature. The sooner the engine goes into closed loop operation, the lower are its emissions. A faulty coolant sensor, oxygen sensor or thermostat can prevent the engine from going into closed loop. This usually causes the engine to run rich and pollute.

Code Reader: A type of diagnostic tool that plugs into the OBD II diagnostic connector and displays fault codes. A code reader can also be used to clear codes, and some will show OBD II readiness flags, but most are not capable of reading sensor data or other system information.

Downstream O2 sensor: The oxygen sensor located behind (downstream) of the catalytic converter. This sensor is used primarily to monitor the operating efficiency of the catalyst, but may also be used for long term fuel trim.

Drive Cycle: When the engine is started, allowed to reach operating temperature and then shut down. It may or may not involve actually driving the vehicle.

Enable Criteria: The set of conditions needed for a diagnostic test or OBD II monitor to run.

Fuel trim: This is the fine-tuning of the air/fuel mixture. There is both short term fuel trim and long term fuel trim. Short term compensates for changing operating conditions. Long term compensates for engine wear and other variables.

Loaded Mode Testing: A type of emissions testing that places a load on the vehicle to simulate driving conditions. This is done on a dynamometer while the vehicle is driven at various speeds. Loaded mode testing is used in both I/M 240 and ASM emissions testing.

Misfire Detection: An OBD II monitor that detects misfire in one or more cylinders. Misfire may be caused by ignition, fuel or compression problems. If misfires exceed a certain rate, it sets a misfire code which corresponds to the cylinder(s) involved. If the misfire jumps around from cylinder to cylinder, OBD II sets a "random misfire" code (P0300) which maybe the result of a vacuum leak, EGR leak or low fuel pressure.

Monitor: A self-diagnostic check run by OBD II on a system or component.

Open Loop: An operating mode of the fuel feedback control system where the fuel mixture is fixed (unchanging) and is predetermined by the computer. The engine remains in open loop after it is first started and until it reaches a certain temeprature and the oxygen sensor is hot enough to produce a good signal.

Readiness Code or Flag: An indication that a particular OBD II monitor has run or has been completed. Emission test requirements requires that all by one or two readiness monitors be completed before a vehicle can pass an OBD II emissions test (NOTE: this requirement varies by model year and state).

Scan Tool: A type of diagnostic tool that plugs into the OBD II diagnostic conenctor to access system information including fault codes, history codes, sensor data and other information. Professional grade scan tools are also "bidirectional" and can be used to perform special tests. Some can also be used to reprogram the vehicle computer.

Trip: Driving the vehicle long enough and under the right conditions so that all the OBD II system and component monitors have run at least once.

Upstream O2 sensor: The oxygen sensor located in the exhaust manifold and ahead (upstream) of the catalytic converter. This sensor is used by the fuel feedback control system to monitor the relative richness or leanness of the air/fuel mixture for emissions, fuel economy and performance.

Warm-up Cycle: Starting a cold engine and allowing it to warm up at least 40 degrees F (22 degrees C) and reach a minimum of 160 degrees F (70 degrees C).


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