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OBD-II Acronyms and Jargon

OBD-II Acronyms and Jargon

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
  • 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


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