Short, plain-English definitions of the maintenance, diagnostics, and EV terms you'll run into — from DTCs and VIN to MPG, L/100km, and state of health.
OBD2 is the standardized self-diagnostic system built into nearly every car sold in the U.S. since 1996. It continuously monitors the engine and emissions systems and exposes fault codes through a universal 16-pin port, readable by any compatible scanner or app.
OBD2 fault codes explained guideA DTC is a standardized five-character code (one letter, four digits) that a vehicle stores when its OBD2 system detects a fault. The code identifies the affected system and subsystem — for example, P0301 is a cylinder-1 misfire. Look one up in our OBD2 fault-code reference.
OBD2 fault codes explained guideThe check engine light is a dashboard warning that the OBD2 system has stored a fault code. A steady light is generally non-urgent; a flashing light indicates a severe misfire that can damage the catalytic converter and needs prompt attention.
OBD2 fault codes explained guideA catalytic converter is an emissions-control component in the exhaust system that chemically converts harmful gases into less harmful ones. It is one of the most expensive emissions parts, which is why codes like P0420 should be diagnosed carefully before replacement.
OBD2 fault codes explained guideOEM refers to parts made by, or to the specification of, the company that built the vehicle. OEM parts match the original components exactly; aftermarket parts are made by third parties and vary in quality and fit.
A VIN is the unique 17-character code that identifies a specific vehicle. It encodes the manufacturer, model, year, and plant, and is used for registration, recalls, insurance, and history reports.
A recall is a manufacturer- or regulator-issued notice that a vehicle has a safety defect or fails to meet a standard, requiring a free repair. Owners are notified by VIN, and open recalls can be checked against a vehicle's VIN at any time.
MPG measures fuel economy as the distance a vehicle travels per gallon of fuel — higher is more efficient. It is the standard fuel-economy unit in the United States; much of the rest of the world uses L/100km.
L/100km expresses fuel consumption as the litres of fuel used to travel 100 kilometres — lower is more efficient. It is the standard metric fuel-economy unit and is inversely related to MPG.
Regenerative braking is a system, common on EVs and hybrids, that recovers energy during deceleration by running the electric motor as a generator to recharge the battery. It also reduces friction-brake wear, though the brake fluid and hardware still need periodic service.
EV maintenance schedule guideState of Health is a measure of an EV (or hybrid) battery's current usable capacity relative to when it was new, expressed as a percentage. A gradual decline is normal; tracking it over time reveals the pack's real condition better than any single reading.
EV maintenance schedule guideAn HPDE is an organized, instructed event where drivers learn high-performance and car-control skills on a racetrack in a controlled, non-competitive format. It is the most common on-track entry point for enthusiasts.
A track day is an event where drivers take their own street or track-prepared cars onto a closed circuit to drive at speed safely, outside of public roads. Lap times and car setup are commonly logged to measure improvement.
A service interval is the recommended frequency for performing a given maintenance task, defined by mileage, time, or both — with the rule being to act on whichever comes first. Intervals come from the vehicle's owner's manual.
How to track car maintenance guideThe powertrain is the group of components that generate power and deliver it to the wheels — the engine or electric motor, transmission, and driveshafts. OBD2 codes beginning with the letter P refer to powertrain faults.
OBD2 fault codes explained guide