See Figures 1, 2, 3, 4 and 5
The BMW crankcase emission control system is considered a sealed system. Rather than purging the crankcase of blow-by vapors with fresh air is done conventionally, the blow-by emissions are routed directly to the air cleaner or air collector with crankcase pressure behind them. Since the purpose of the PCV valve in conventional systems is to regulate the volume of purging air even with varying intake vacuum, this valve and the maintenance associated with it are eliminated.
The Crankcase Emission Control System is virtually maintenance-free. The connecting tube from the top engine cover to the air cleaner or air collector should be inspected during the routine maintenance services and replaced if cracked, distorted or plugged.
With the engine operating and the connecting tube disconnected, a vacuum should be noted at the air cleaner or air collector side of the hose. If vacuum is not present, an air leak or plugged air induction system may be the cause.