Toyota 1NZ

Toyota's 1.5-litre four, and one of the highest-volume engines in the world — the Yaris, Vios, Belta and, as the 1NZ-FXE, the first- and second-generation Prius. An aluminium block with chain drive and VVT-i, designed for low cost and long life rather than output.

It has no single characteristic failure, and that is itself the useful diagnostic fact. Where these engines misbehave, the cause is almost always maintenance or a consumable — ignition coils, the crankshaft or camshaft position sensor, carbon around the throttle body, or a stretched chain on a car that has run on long intervals. Pattern-matching from a European turbo engine's failure list will send you nowhere here.

The hybrid 1NZ-FXE deserves the same caution as the Prius 2ZR: it runs on the Atkinson cycle within a hybrid system, so complaints about starting, charging or idle behaviour need reading against the hybrid control strategy before any engine component is suspected.