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 front suspension of the longitudinal engine Audis (and the Seat Exeo derived from them) works with four control arms per side: two above, two below. That gives excellent steering when new, but it also means four ball joints and eight bushes per side: sixteen wear points at the front in total.

Channels around the sunroof frame carry the water away, leaves, dust and dirt block them, the rubber valve at the end of the channel sticks shut, and the water runs into the headlining, the A-pillar, the footwell and the boot. On the B8 A4 this often leads to electrical faults: you often miss the water and notice instead that something electrical starts behaving oddly, and by then the control unit in the floor is already corroding. Cleaning the drains is a cheap repair, replacing a soaked control unit is expensive.

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.