The PCV is the positive crankcase ventilation system. Because your crankcase is sealed, temperature changes, primarily between operating temperatures and environmental differ, pressure changes occur. Because the crank case holds oil, as well as gasoline, hydrocarbons, combustion byproducts, etc, they are rather harmful to the environment, yet have value in that they can be reburned. As such, the PCV vents said gases back into the intake stream where it is reburned. Where is it on the 850? It is under the intake manifold. How can you check for proper operation? If you don't have a code, it is functioning within normal parameters. But this does not mean that the PCV valve may not be partially clogged. How can you extend the life of the PCV valve/system indefinitely? Run only clean 91+ octane gas (but not too high), keep extreme driving conditions to a minimum, keep oil loss to a minimum (especially from the turbo), use a high quality synthetic engine oil, use a high quality injector cleaner and intake cleaner such as BG's line of products, regularly. Basically, keep gunk/varnish/carbon deposits/ and other combustion and petroleum product by products to a minimum.