Scion 12204-28030 PCV Valve

The Positive Crankcase Ventilation (PCV) system reduces hydrocarbon emissions by scavenging crankcase vapors. It circulates fresh air from the air cleaner through the crankcase, mixing it with blow-by gases. The mixture is rerouted through a PCV valve to the intake manifold. The PCV valve restricts flow when intake manifold vacuum is high, maintaining idle quality. In abnormal conditions, excessive blow-by gases flow back through the crankcase vent tube into the air cleaner for normal combustion. The PCV system consists of the PCV valve, blow-by filter, and vacuum hoses connecting these components to the engine. Regularly checking and replacing the PCV valve is important.