The balance shaft module drives the oil pump through a hexagonal shaft stub. That hex and its mating part gradually round off, until the shaft finally turns freely: the oil pump stops and the oil pressure is gone. The process gives no warning, and that is exactly what makes it dangerous. The failure typically happens at high revs, and the oil pressure light comes on only once the damage is already done. The factory hex is undersized, so it knocks against the wall of the bore, and the wear accelerates itself. The maker classed it as a "tolerance deviation" and, given the small number of cases against total production, did not recommend preventive repair; Audi alone ran a service action (13D7). The replacement is expensive: on the German market the module replacement is 1,300 to 1,700 euro, and an independent repair touching only the hex is around 650 euro. The reported cases cluster around the Passat B6, Sharan, Audi A4/A6, Superb and Alhambra, in model years between 2005 and 2009. This layout is not only on the pump-injector (PD) engines, it is on the common rail EA189 engines too: the same module, the same hex, the same wear. The failure is typically reported between 100,000 and 160,000 km. The first sign is a short flash of the oil pressure light, in a long bend or a few seconds after a cold start, and then quiet again. The versions without balance shafts (BKD, BMM, BMN, AZV) drive the oil pump differently and are not affected by this wear. If the light stays on or flashes, stop as soon as it is safe, switch the engine off, and do not restart it until the oil pressure has been measured.

The seven speed, wet clutch DQ500 is the DSG of the high torque models (Transporter, Arteon, Tiguan). On a heavy vehicle, on the T5 vans, the splined joint of the differential can shear. Clutch debris blocks the valves of the mechatronics unit, and it jerks on shifts. The pressure sensors fail at around 100,000 to 150,000 km, and then either the even or the odd gears drop out. The control board fails from overheating next to a clogged heat exchanger. It is not repairable, only replaceable.

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.

The most common complaint on the Q3 is the infotainment system: the touchscreen does not respond, dash warnings flicker, the system freezes, or a sensor is faulty. One survey found a fault of this kind on 44 per cent of Q3 cars, and half of the repairs spent more than a week in the workshop. A software update fixes many cases and the update is free, so before you buy, ask whether the latest version is installed.

The dash shows "Error: Workshop! Only leave vehicle in position P" with an audible warning. The message appears in whatever language the car is set to, for example "Fehler: Werkstatt! Fahrzeug nur in Stellung P verlassen" in German.