The fix: replacing the electric switching valve and a software update. The campaign started at the end of 2021; the affected group is the C-Class, E-Class and other OM654/OM656 models.

A recall on the model does not mean it was carried out on this car. Only the franchised dealer can tell you, by VIN.

1) Roller finger followers (Rollenschlepphebel). According to the German technical press, on some cars the followers wear early at around 100,000 to 120,000 km. On 10 July 2018 the maker introduced a strengthened follower from engine number 80278367 (new part number A6540505701 in place of the old A6540501100). On early built cars the risk is higher. A faulty follower develops so much heat that the removed metal shows blue discolouration (Anlaufspur).

2) Oil dilution. The post injection needed to regenerate the particulate filter puts diesel fuel into the engine oil. With short urban use the engine does not get warm enough, the fuel does not evaporate, the oil thins out, and the follower and valvetrain are exactly what suffers most from poor lubrication.

The timing chain sits on the gearbox side: if it stretches, the replacement is labour intensive. There are few complaints of a broken chain, but on the early series about 5,000 cars were recalled for a weak chain, and the Tritan 15 coating was changed to Tritan 18.