If left unmanaged, blow-by gases build excessive pressure inside the crankcase, causing catastrophic oil leaks through main seals. The Positive Crankcase Ventilation (PCV) system safely routes these gases out of the crankcase and back into the engine intake manifold to be cleanly burned away.
For a precise diagnosis, always refer to the document for your specific VIN, as Mercedes frequently updates component locations and test plans. mercedes-benz p1d687a