P2279 fault code.

The crankcase breather module keeps the pressure inside the engine at the right level with a membrane. On this V8 the membrane lets pressure through, and from then on the intake draws air and oil vapour out of the engine without regulation. The audible sign is a metallic whistling or grinding noise from the engine bay at idle, which typically only comes when the engine is warm, while the engine warning light is sporadically on. The engine control unit stores P2279 for an intake system leak and P0507 for a raised idle. The oil reaching the intake increases oil consumption, gives blue smoke under load, and leaves an oily film inside the intercooler. In March 2016 Audi issued a service bulletin for this (17-16-70) and named the 2013 to 2016 A6, A7 and A8 with the 4.0 TFSI engine. The factory solution is a fabric-reinforced inner membrane, meaning the breather module is replaced. The module sits between the two cylinder banks, under the intake, so the job also needs the coolant drained, and the replacement costs between 400 and 1,800 euro. The problem is reported above 100,000 km.

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.