A small electric motor built into the rear brake calipers applies the parking brake. This is a known weak point of the B8 platform (A4 B8, A5 8T, Q5 8R, allroad B8): moisture and road salt get into the motor housing, the electronics corrode, and the gears seize. The symptom is a parking brake that will not apply or will not release, with a fault message.

The drains of the fabric roof block up with leaves and dust, the seals wear out over the years, and water runs into the rear footwell, behind the side trim and into the boot. The roof electronics and the switches fail too, and then the roof stops halfway or does not start at all. Soaked connectors are ruined, the roof repair costs parts and labour, and if it stops halfway in the rain the cabin gets soaked.

The combined housing of the water pump and the thermostat is plastic, and it is bolted directly to the hot engine block. The many heat and cool cycles warp it, it becomes brittle, and then it develops a hairline crack: the fault is almost always the housing, not the pump itself. The signs are slowly disappearing coolant with no visible puddle, the coolant level light, a sweet smell from the engine bay, and later a pink stain under the car. The repair means replacing the pump and the housing together, and the intake manifold has to come off for it: 4 to 6 hours of work. It shows up on model years 2015 to 2025.

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 crankcase breather carries the vapour that forms inside the engine back to the intake, and a rubber membrane regulates the pressure. Oil and heat harden this membrane until it tears, and from then on the intake draws air through the hole in it. The engine control unit does not measure that air, so the mixture goes wrong: the engine shakes at idle, stumbles when accelerating, and the fault memory gets P2279 for an intake system leak. In the other direction oil starts towards the intake, which leaves an oily film in the intercooler and on the intake pipe and speeds up the carbon build-up on the intake valves. The audible sign is a whistling or hissing noise from the engine bay, loudest at idle. The tear is reported between 60,000 and 90,000 km. On the first and second generation the breather is a separately replaceable valve (factory number 06H 103 495 AK) and costs between 80 and 400 euro; from the third generation it is built into the cam cover, so there the cover is replaced. The maker issued three versions up to 2016, and fitting the pressure variant that does not belong to the engine brings the same symptom back.

On the Sportback and the convertible the fuel flap often sticks, it does not open from the button or it stays open, and this shows up on cars built between 2010 and 2016. The part is cheap, but you still cannot refuel while the flap stays shut, and on a test drive it takes half a minute to check.