Fuel trim practice by fault family, TrimCase

Pick a family and a tier

Fault family

Unmetered airAir or vapour that reaches the cylinders without passing the MAF: a vacuum leak, or a purge valve stuck open.Vacuum leak, Purge stuck openAir meteringPremiumThe MAF reading low or high, and an exhaust restriction that caps how much air the engine can breathe.MAF reads low, MAF reads high, Restricted exhaustFuel supplyPremiumFuel pressure too low under load, too high everywhere, and an injector that drips when it should be shut.Weak fuel supply, High fuel pressure, Leaking injectorExhaust and sensorsPremiumThings that make the upstream sensor lie: an exhaust leak ahead of it, a biased sensor, a misfiring cylinder.Exhaust leak, Biased upstream sensor, MisfireCoolant temperaturePremiumA coolant sensor stuck at a cold reading, and a thermostat stuck open that never lets the engine warm fully.ECT stuck cold, Thermostat open

Tier

Single fault, cleanSingle fault, noisyTwo faultsPremium

Eight cases. The answer list always holds every fault, so a family narrows what comes up, not what you can pick. About one case in eight is the healthy control.

Reading your saved practice.

Want the free round instead? The daily drill is five mixed cases, new every day.