OBD-II Diagnostics Glossary
Concise explanations of 30+ core OBD-II terms — DTC, ECU, PID, MAF, lambda sensor, EGR, DPF, EVAP, fuel trim and more.
OBD-II basics
Diagnostics
- DTC Diagnostic Trouble Code — fault code from the ECU.
- VIN Vehicle Identification Number — unique vehicle identifier.
- Fuel Trim Fuel trim correction (STFT + LTFT).
- Misfire Cylinder fails to combust normally.
- Closed-loop Closed-loop fuel control mode.
- Limp mode Engine safe mode.
- Freeze frame Snapshot of parameters at fault time.
- Pending code Unconfirmed fault code.
- Drive cycle Standard driving pattern for readiness monitors.
- Readiness monitor ECU self-test status flag.
- Stoichiometric AFR 14.7:1 — ideal air-fuel ratio for gasoline.
- Boost pressure Turbocharger intake pressure.