The front bearing of the mechanical supercharger on the 3.0 TFSI, the nose bearing, wears, and over the years and the kilometres it drones louder and louder, but only under load. If the bearing seizes, the supercharger is destroyed inside. You will not hear the noise with the engine idling, so the test drive has to include a firm acceleration.

The 7 speed wet clutch S tronic used in the longitudinal engine Audis (0B5 / DL501) is more durable than the early DSG units, but the mechatronics unit is the most common source of faults here too. As the solenoids wear, the regulation of the hydraulic pressure deteriorates: harsh or missed shifts, delayed D/R engagement, and finally limp mode.

With direct injection the fuel does not wash the intake valves: the petrol goes into the cylinder, not behind the valve. The oil mist and soot arriving through the EGR and the crankcase ventilation therefore build up on the valve stem and head, and from 80,000 to 100,000 km they restrict the flow. Symptoms are hesitation, loss of power, a rough cold start and misfire. It is not a part failure: it is a consequence of the design, and therefore it comes back. Cleaning (walnut or dry ice blasting) helps for a few tens of thousands of kilometres.

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.