Peugeot DW10 (2.0 HDi)

PSA's 2.0-litre common-rail diesel and the larger sibling of the DV6 — fitted across Peugeot, Citroën, and (as the earlier 2.0 TDCi) Ford, Volvo and Mini. A long-lived, generally well-regarded engine that has run through several emissions generations.

The recurring items are the variable-geometry turbocharger, whose vanes stick with carbon and produce a boost fault that often frees with cleaning rather than replacement, and the diesel particulate filter — on the earlier cars an additive-based (FAP) system with its own fluid reservoir and its own set of faults that look like filter faults but are not.

Injector wear producing a rough cold idle, and EGR cooler blockage, complete the list. The additive system deserves particular mention because an empty or unregistered additive tank prevents regeneration entirely, and the resulting cascade of filter codes reads as a failed filter on a car whose filter is fine.