The high pressure fuel pump wears from the inside, and metal dust forms in the friction pairs. The debris gets into the system and blocks everything there. The wear is reported above 160 000 kilometres, and the upper limit of the pump's life is around 200 000 kilometres, beyond which an overhaul is needed.

The metal dust travels on to the injectors and destroys those too, so a pump fault easily turns into a repair of the whole injection system: the system has to be flushed and the injectors replaced. The pump can also give up suddenly, even on a motorway, and the engine then stops while driving.

The injectors themselves also give up at around 200 000 kilometres, and their symptoms are easy to recognise. The most characteristic is difficult starting on a warm engine. With it comes damaged atomisation at the nozzle, a back-leak through the worn nozzle which makes starting worse still, and fuel getting into the crankcase and raising the oil level.

That last sign is the one that can be caught on the dipstick: if the oil has risen above MAX and smells of diesel, it belongs to the injection system.