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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
TECHNICAL TERMS
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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