When a positive crankcase ventilation, or PCV, valve goes bad, the valve may be plugged and can cause sludge to build in the engine, as well as oil leaks. A PCV valve can also go bad when there is water inside of it caused by moisture contamination. In this instance, the PCV valve needs to be replaced.
One way to tell that the PCV valve has gone bad is if the vehicle's check engine light turns on. It can also cause noise, such as a whistle or whining sound. In some cars, a bad PCV valve will cause oil to blow into the air filter.
PCV valves do age, and as they get older, sludge may cause them to stick in the open position. Fortunately, they are easy to replace once the location of attachment is found. They usually last about 50,000 to 80,000 miles before they need to be replaced, but a series of short trips can cause the valve to need replacement before the 50,000 to 80,000 mile mark is reached.
The PCV valve reduces blowby emissions from the engine of a vehicle. Their condition can easily be checked by shaking them to see if there is a rattling sound, or using a flow tester to test valve performance.