This system is found only on diesel engines
See Figures 1 and 2
The Crankcase Depression Regulator (CDR) is designed to scavenge crankcase vapors in basically the same manner as the PCV valve on gasoline engines. The valve is located by the right cylinder head cover. On this system, the valve and filter are replaced as an assembly.
The ventilation pipes and tubes should also be cleaned and replaced as wear and tear dictates.
Do not attempt to test the crankcase controls on these diesels. Instead, clean the valve cover filter assembly and vent pipes and check the vent pipes. Replace the breather cap assembly every 30,000 miles (48,000 km). Replace all rubber fittings as required every 15,000 miles (24,000 km).