This is the most common N54 fault, and it affects early N55 engines too. The pump is a two part design: fuel goes into one half and lubricating oil into the other, and the sealing ring separating them ages over time. That is what drops the pressure.

The very first symptom is a long crank: the engine does not catch straight away but turns over for several seconds. Later you get a rough idle, misfire, loss of power, and finally limp mode, which can reach you at the side of the road.

The fault code is typically P0087 or P0089. If the control unit also returns a camshaft timing code (P0011, P0012), that is often not a separate fault but a consequence of the pressure drop: it is worth ruling the pump out first.

The 2007 to 2009 cars are the worst; the maker revised the design after that.

The N53 (the lean burn six cylinder sold in Europe) got the same pump. Faults were reported on it. It is not known whether they are as frequent as on the N54, because the N53 was not sold in the USA and there is no official complaint data on it.