Mercedes-Benz OM668

Mercedes-Benz's 1.7 diesel — the OM668 — in the first two A-Class generations and the Vaneo.

It was the first common-rail engine Mercedes put in a small car, and it is a genuinely compact design: the A-Class packages its engine at an angle beneath the floor, which is what makes access to almost everything worse than the engine itself deserves.

Its known items are the injectors and the turbocharger, both ordinary for a first-generation common-rail diesel, and the sandwich-floor packaging is what turns either into a large job.

It is chain-driven, which removes the belt question that dominates its contemporaries — but the chain is not maintenance-free and a rattle on a cold start is the warning.

The OM640 that replaced it in the W169 is a different engine with its own page here, and the two are frequently confused because the W169 carried both.