Scion 12204-28020 Valve Sub-Assy, Ventilation

The Positive Crankcase Ventilation (PCV) system reduces hydrocarbon emissions by directing blow-by gases and crankcase vapors into the intake manifold. Fresh air from the air filter housing mixes with these gases in the crankcase before exiting through the PCV valve. During idle and part-throttle conditions, blow-by gases flow through the PCV valve into the intake manifold, while fresh air is drawn into the crankcase. Over time, sludge buildup may reduce the system's efficiency and cause leaks. Regular checks and possible replacements of the PCV valve and hoses during routine maintenance are recommended.

The Positive Crankcase Ventilation (PCV) system reduces hydrocarbon emissions by cutting crankcase vapors. It does this by circulating fresh air from the cleaner to the crankcase, mixing it with blow-by gases. These gases are moved through a PCV valve and taken back to the intake. The PCV has the PCV valve, a blow-by filter, and vacuum hoses connecting them to the engine. The PCV valve is intended to block flow during high-intake vacuum conditions to maintain consistent quality. If there is anything unusual, the system allows blow-by gases to go back into the air cleaner from the vent tube.

With the engine idling at normal operating temperature, place your finger over the valve opening. If there's no vacuum at the valve, check for a plugged hose or valve.