The common rail high-pressure pump is lubricated and cooled by the diesel itself, because the pump produces over 2,000 bar and has no separate lubrication circuit. If that lubricating film breaks down, the internal running surface of the pump eats itself and metal debris is produced. The debris travels through the whole system with the diesel, the rail, the injectors and the tank as well, because the return line carries it back and the lift pump draws it in again at every start. From there flushing the injectors does not help, all of them have to be replaced and the tank cleaned too. The failure is reported between 120,000 and 160,000 km, and the repair runs from 1,500 to 15,000 euro depending on how far the debris got. The lubricating film is broken by misfuelling and by long runs with an almost empty tank, because below 5 litres the lift pump also draws air. Plain wear of the pump is a different case: there is no debris and only the pump has to be replaced.
What to check
- Ask when the fuel filter was last changed, and ask for the old filter if it is kept
- Look for silvery, shiny metal particles in the filter housing and on the filter
- Ask whether there has been a misfuelling, and whether the car often ran on an almost empty tank
