What makes the repair expensive: once the inside of the pump wears, metal debris travels through the rail and contaminates the entire fuel system. At that point replacing the pump is not enough: the injectors, the rails, the tank and the lines go with it. That is the difference between a "pump replacement" and a "full system replacement" quote, that is what you should ask about.

The maker started a recall for this in the United States (NHTSA 21V586000, 2014 to 2018 328d / X5 xDrive35d / 535d / 740Ld / X3 xDrive28d). The same campaign did not run in Europe, even though the same pump works in the 320d/520d/X3 20d versions that are common right across Europe. The recall does not cover these cars.

The engine or the gearbox has to come out for the replacement, so the labour is a multiple of the parts cost. If the chain breaks or jumps, the engine is badly damaged inside, and the repair is an engine rebuild.

The problem is worst on engines built between March 2007 and March 2011, and the ones before early 2009 are the worst of all. The maker handled it under a service campaign in several European markets, but in the United Kingdom there was no formal recall. "It was never recalled" does not mean the chain is fine.

According to the German technical press the fault affects the whole N47 series and every power output, inspection is advised from 100,000 km, and factory revisions closed the matter around 2013, so cars built after 2013 are in a significantly better position. Stretching is typically preceded by a distinct rattle.

The maker recalled the 2013 to 2018 four and six cylinder diesels, roughly 800,000 cars worldwide. The first repair attempt proved insufficient, and the leak returned in several cases: the cooler fitted since 2022, from a different supplier, is the valid fix.

So "the recall was carried out" is not enough on its own: you have to check when, and which repair was done. A first round repair does not by itself rule the problem out.

The early symptoms are white, sweet smelling exhaust smoke, slowly dropping coolant, and a rough idle.

It shows up on diesels built between 2013 and 2018. The earlier M57 is not covered by the recall.

The first is wear of the clutch pack and the fluid: in a slow, tight corner (a car park, a roundabout) the car jerks and "hops", as if the drive grabbed and let go. You can also get a jerk when pulling away on a slope. The second is the plastic actuator gear: the position signal is lost, the brake, ABS and 4x4/DSC lights come on together on the dash, and a clicking is audible from the transfer case when you switch the ignition off.

Workshops often propose a full transfer case replacement straight away. But the plastic gear can be replaced on its own, and the wrong tyre size or a mixed set of tyres also imitates the jerking, because the transfer case then slips continuously. So clear up the tyres and the fault code first, before you pay for a transfer case replacement.

A "compressor replacement" on its own often does not fix it: if the air spring keeps leaking, the new pump fails soon too. Air suspension is not fitted to every version, so the equipment list has to be checked separately.

The repair starts with finding the leak (soapy water, ride height sensor, valve block), not with replacing parts blind.

The first is the mechatronics unit: the valve body and the control electronics in one. If the solenoids or the pressure regulation weaken, the gearbox jerks, the D/R engagement is delayed, it logs a gear ratio fault code, and finally drops into limp mode (often staying in 2nd or 3rd).

The second, and often misdiagnosed, is the connector sleeve of the mechatronics unit: the O-ring of the plastic sleeve ages, and ATF leaks from the side of the housing, exactly where the wiring harness enters. This is easy to mistake for a rear crankshaft seal. The trail starts from the driver's side of the housing, not from the clutch side.

On cars built in 2023 there was also a separate safety recall for a welding fault in the mechatronics unit. That is not the same as the wear related sleeve and the valves.

Check the fluid level, the area around the sleeve and the fault codes first; do not accept a "full gearbox replacement" quote straight away.

The fault is often not the "expensive motor" but the wiring fraying at the hinge. And that can only be found with the trim off. If the seller says "the spindle has already been replaced" but the wiring is damaged, the fault will come back.

This applies only to versions with the powered tailgate.