The most common source of faults on the longitudinal 7 speed S tronic that replaced the DL501 (0CJ / 0CK / 0CL) is the mechatronics unit as well. Typical faults are the input or turbine speed sensor (which makes the shifting unpredictable), clutch slip under load, and abnormal operation of the park lock.

The four groups of parts in the air suspension (compressor, valve block, ride height sensors, air springs) work together, and any weak link causes a fault message, an uneven ride height or a car that settles. The characteristic symptom: the car sits down on one corner overnight, levels itself for minutes in the morning, and the compressor runs long and loud. According to the reports the compressor lasts 80,000 to 100,000 km; and a leaking air spring takes the compressor with it, because it keeps trying to make up the loss.

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.

The crankcase ventilation (PCV) of the third generation 1.8/2.0 TSI fails less often than its predecessors, but it is not faultless. After sustained full load acceleration, under hard braking, the return branch of the ventilation can be overloaded, and the oil ends up in the intake instead of draining. The symptoms are oil consumption, blue smoke after load, and deposits in the intake.

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.

The per cylinder ignition coil of these direct injection, turbocharged petrol engines fails. According to the Haynes service material this and similar simple electrical faults account for roughly eighty per cent of workshop visits.