Mercedes-Benz M274

The longitudinally mounted four-cylinder petrol of the C-Class and E-Class, in 1.6 and 2.0 litre forms — direct injection, turbocharged, and the volume petrol engine of those cars for a decade. Its transverse sibling is the M270, mechanically closely related but fitted to the front-drive A-Class and B-Class; the two are frequently confused and a part number for one is often wrong for the other.

It also appears outside Mercedes-Benz: Infiniti fitted it to the Q50, which is the kind of cross-badge fact a per-vehicle reference cannot state.

The recurring complaints are camshaft adjuster (variable valve timing) wear producing a rattle on start-up and timing codes, the usual direct-injection intake-valve carbon, and — on higher-mileage examples — the balance shaft and chain. A cold-start rattle that lasts a second or two before oil pressure builds is the pattern to recognise.