Toyota AD (1AD / 2AD)

Toyota's 2.0 and 2.2 common-rail diesel — the 1AD and 2AD — in the Avensis, Auris, RAV4 and Corolla Verso.

⚑ This family has the worst reputation of any modern Toyota engine, and saying so is more useful than a generic fault list. Cylinder head cracking and head gasket failure are a documented pattern on the 2AD-FHV in particular — Toyota extended warranties over it — and the symptom is coolant loss with no external leak, later pressure in the header tank.

The injectors are the second known item and their failure is cylinder-specific and code-setting. Injector seals leak combustion gases up around the injector body, which carbons the seat and makes removal a job in itself.

The particulate filter is where most running complaints originate, and the duty cycle that breaks it is short urban journeys: the filter never reaches temperature, and a rising oil level on the dipstick is fuel dilution rather than a servicing error.

The later 1WW, 2WW and 1GD engines replaced it and share almost nothing with it, which is worth establishing before applying anything written about a Toyota diesel.