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 short circuit and the fire can happen while the engine is switched off, and also while the car is parked. A car standing in a garage can catch fire too.

According to the German technical press, in January 2021 around 430,000 cars in Germany and more than half a million worldwide were recalled for this, all E90/E91/E92/E93 3 Series. In the USA more than 700,000 2006 to 2011 3 Series cars had already been recalled for the same thing in autumn 2017, after claimants in three separate cases cited injuries. The maker disputed that the fault had ever caused personal injury or an accident.

The EU Safety Gate names it in two separate alerts: the 3 Series (A12/00390/21) and the X5/X6 (A12/01261/21).

The campaign is free, but only if it was carried out. On a fifteen year old car, ask about it, because nobody will offer it unprompted.

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.

The symptom is a whistling or grinding noise from the turbos, limp mode under load, and power falling away in the upper rev range. Codes pointing to boost pressure appear in the fault memory.

Failures are reported between 60 000 and 120 000 miles, that is between roughly 96 000 and 193 000 kilometres. One thing is worth knowing: a specialist workshop can rebuild the actuator, and that costs far less than a complete turbo replacement. One repair comes to between 400 and 2500 pounds, while a complete turbo costs between 1800 and 3500 pounds each.

The triple turbo version is noticeably less reliable than the single or twin turbo variants: they do not have this failure pattern. If on such a car there is no actuator repair at all in the history past 100 000 miles, that is a bad sign, not a good one.

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 most important thing to know is that the control unit does not signal this: no lamp comes on for low oil pressure, and no fault code is stored either. The symptom is a quiet ticking at idle and a metallic noise under load, and at the rod bearing this is often explained by something else. It can be measured, though: a workshop connects a gauge and reads the real pressure at idle at operating temperature, and below 1.2 bar the engine is running in the period that causes the damage.

The length of the oil change decides matters on this engine. A change between 10 000 and 20 000 kilometres protects the bearing, the long factory interval does not. If the main bearing turns, the crankshaft is damaged too, and the upper half of the main bearing bed is aluminium while the lower is steel, so repairing the crankcase is difficult, and the block often goes out cracked and beyond repair. As prevention an uprated oil pump exists, with larger gears and its own pressure regulator, between 800 and 1150 euros, without fitting.

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.