This is word for word from ALLDATA for the explination of the PCV system
Engine Ventilation
The engine ventilation is pressure-controlled. Depending on the intake pipe partial vacuum and charge-air pressure, venting takes place either via a 6-way distributor rail in the inlet ports or into the fresh air pipe before the exhaust turbocharger (cylinders 4 to 6). The distributor rail is integrated in the cylinder head cover.
Two valves are fitted for engine ventilation.
Non-return valve with pressure limitation The non-return valve with pressure limitation regulates the flow depending on the applied intake pipe partial vacuum and controls the introduction of the blow-by gases into the inlet ports.
As of a defined charge-air pressure, the non-return valve closes with pressure limitation.
Non-return valve to the fresh air pipe The 2 fresh air pipes are arranged after the intake muffler. Each of the 2 fresh air pipes connects the air filter to an exhaust turbocharger. In the fresh air pipe, the air cleaned in the air filter is transported to the compressor.
As of a defined charge-air pressure, the prevailing partial vacuum in the fresh air pipe opens the non-return valve. The blow-by gases are vented into the fresh air pipe to the exhaust turbocharger (cylinders 4 to 6).
The ventilation connection to the fresh air pipe has an engine ventilation heating system based on the PTC principle (positive temperature coefficient). The engine ventilation heating is activated via terminal 87.