On these engines the oil pump is driven by its own small toothed belt, and that belt runs in the hot engine oil. This is not the large timing belt that drives the camshafts, it is a separate belt in the lower part of the engine. In the oil the rubber hardens over time, its surface starts to crumble, and the loose particles block the suction side of the oil pump, so the oil pressure drops. If the belt snaps, the oil pump stops at once and the engine is left without lubrication within seconds. The rubber crumbs can also ruin the turbocharger and the camshaft adjuster, because they are lubricated from the same oil circuit. The maker specifies no replacement interval for this belt, so most cars still carry the one fitted at the factory, and the failures are reported above 150,000 km. Oil outside the specification and a stretched oil change speed the process up, because this belt ages in the oil. Replacing the belt itself costs between 200 and 600 euro, as long as the engine has not run without oil pressure.

On short urban trips the particulate filter cannot burn through. The engine control unit then injects extra fuel late in the cycle to heat the filter, and part of that fuel passes down the cylinder wall into the sump. The oil level rises, the oil thins out, and it lubricates worse.

The EGR valve and its cooler block up with soot and oily deposits; the particulate filter cannot regenerate on short urban trips. The signs are reduced power, a warning light, and frequent regeneration. The software update after the diesel emissions affair made the EGR operate more often, which accelerated the phenomenon: the maker gave goodwill repairs in several cases.

On this engine the water pump is driven by the timing belt, and the plastic impeller of the pump, along with its electronically controlled shut-off ring, is the weak point: the ring sticks, and the impeller separates from the shaft or disintegrates. The first sign is slowly disappearing coolant and heating that stays cold for a long time. The real risk is not the price of the pump: the leaking water washes the grease off the timing belt rollers, and from then on the belt is what fails. If the timing belt snaps, the engine is badly damaged inside. That is why the two are always replaced together.

The internal springs of the flywheel tire, and the two discs knock against each other. The signs are a rattling or knocking from the bellhousing at idle and when releasing the clutch pedal, and vibration through the floor. If the clutch slips without a burnt smell, that also points to the flywheel. It is worth replacing in time: a disintegrated flywheel can destroy the bellhousing too. At a clutch replacement the two go together anyway.

The vanes of the variable geometry turbo are glued together by soot and oil arriving through the EGR. First you get overboost or a lack of boost, then loss of power above 2,000 rpm, and finally limp mode. Caught in time it is enough to remove the turbo, clean it and fit a new actuator rod. Short urban trips and gentle, low rev driving speed up the deposits.

The G62 sensor tells the engine control unit how hot the coolant is. If it is faulty, the control unit thinks a warm engine is cold, and runs it rich: hard warm or cold starting, a rough idle, markedly increased fuel consumption, and a dash temperature gauge that jumps around or never reaches its usual reading. The part is cheap and can be replaced in half an hour: the trouble is that many people do not recognise it and replace an injector or a lambda sensor instead. If the fault persists, the rich mixture can destroy the catalytic converter too.