What is a PCV valve?

Example of a typical PCV valve

The abbreviation “PCV” stands for Positive Crankcase Ventilation, which is a process that uses the engine vacuum system to “suck” waste gases and other substances from the engine’s crankcase through a special valve, known as the PCV (Positive Crankcase Ventilation) valve, such as the example shown here.  

On most engines, the PCV valve is a simple one-way valve that allows gases to flow through it in only one direction, which is from the engine to the air intake system where the evacuated gases are mixed with the regular intake air/fuel charge to be combusted in the cylinders as a part of the air/fuel mixture.

Note, though, that not all modern engines have PCV valves because, on some late-model vehicles, the crankcase ventilation system connects directly to the valve cover. This arrangement is common on vehicles that have high oil consumption rates as a result of how their engines are designed. We need not delve into the specifics of why some new engines consume as much as one litre of oil per 1000 kilometres driven, but suffice it to say that the absence of a PCV valve on these engines eliminates the possibility of a PCV valve clogging up or failing in some other way.

Note also that on some vehicles, the PCV valve may incorporate a heating element whose function is to prevent the PCV from freezing up in sub-zero temperatures, which, if it happens, effectively blocks the PCV valve. While sub-zero temperatures are not a major concern in the Australian market, some vehicles that were designed to operate in cold climates are imported into the country every year. Thus, if you drive a vehicle with a heated PCV valve, you may encounter fault codes that were set by failures or defects in the PCV valve’s heating element or its associated electrical circuits.   

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