After standing for a longer period, on a cold start you hear a rattling, knocking noise from the timing chain for a few seconds. The cause is oil pressure draining away overnight: the chain tensioner can only tension properly once the oil pressure has built up. A slack chain causes misfires and loss of power, and if it jumps a tooth the engine is badly damaged.

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.

On the infotainment of the B9 platform (A4 B9, A5 F5, Q5 FY) the most common complaint is a black screen, a unit that restarts on its own, and a boot that stops partway. A significant part of these are software in origin, not a hardware fault: an update installed at a franchised dealer resolves it.

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.