Not sure what engine it was but think it was The non turbo one that had a tsb (technical bulletin) where you update The ecu change sparkplugs and clean valves becuse of excsessive sot. Mayby not so helpfull but common on citroen in europ a brand i worked for. The offical failure mode to warrenty The repair was. Anti polution light, porr preformens,sparkplug failure and engine stop when driveing. It was a very big issue atleast in my region/country (sweden) they would warrenty it. Mayby not so helpfull but i rarly seen big fauilers of PSA engines. But if it is a worn piston ring it is more cost effektiv to change engine it takes less time and less likley to damage or improperly repering the engien. ( i know my english is bad but i am working on it 🙂