Renault R9M (1.6 dCi)

Renault's 1.6-litre common-rail diesel, developed with Nissan and fitted to the Mégane, Scénic, Kadjar, Qashqai and X-Trail — the engine that replaced the 2.0 dCi in most applications while producing similar output.

It is a modern, tightly packaged engine with a chain drive and a full emissions stack, and its complaints come mostly from the latter: EGR valve and cooler blockage, particulate filter regeneration failure on short journeys, and on later versions the AdBlue system. Turbocharger failures occur and, as with the K9K, are usually a consequence of oil supply rather than an independent fault.

The item worth flagging is oil dilution during repeated failed regeneration, which raises the oil level and thins it. On a car used for short urban trips, a rising level is the engine reporting a problem with its aftertreatment rather than a mistake at the last service.