Oil Separator
WARNING: This page is about a different car, the 2018 Jaguar XE. However, it is still accessible from the selected car via links, so may be relevant.
Piston blow-by gases are drawn through the oil separator into the engine air intake manifold and added to the air charge. The depression caused by the engine air intake draws gasses from the crankcase, through the oil separator and the hose into the intake manifold.
The resultant depression in the engine oil pan, front covers and cylinder head covers reduces the load on the joint seals in those areas. Engine oil drawn into the oil separator is collected on angled plates in the separator. The oil collects on the plates and falls back to the oil pan via a hole in the cylinder block.