Scion 12204-28020 Valve Sub-Assy, Ventilation

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On models except 1AR-FE four-cylinder engines, the valve should be removed from the hose.

When purchasing a replacement PCV valve, make sure it's for your particular vehicle and engine size. Compare the old valve with the new one to make sure they're the same.

The PCV valve and hose are located in the valve cover.

The Positive Crankcase Ventilation (PCV) system functions to reduce hydrocarbon emissions by directing blow-by gases and crankcase vapors into the intake manifold, where they combine with intake air before entering the combustion chambers for consumption. Fresh air is drawn from the air filter housing through hoses into the crankcase, mixing with blow-by gases and exiting through the PCV valve into the intake manifold. During idle and part-throttle conditions with high intake manifold vacuum, blow-by gases flow through the PCV valve and crankcase ventilation hose into the intake manifold, while fresh air is drawn from the air intake duct through the fresh air inlet hose into the crankcase. Although there's no fixed maintenance interval, the PCV system may become less efficient over time due to sludge buildup inside the PCV valve and hoses. A clogged PCV system might lead to leaking seals. Checking and possibly replacing the PCV valve and hoses during oil filter, air filter, fuel filter, or spark plug changes is advisable.

The Positive Crankcase Ventilation (PCV) system plays a crucial role in reducing hydrocarbon emissions by effectively scavenging crankcase vapors. The system achieves this by circulating fresh air from the air cleaner through the crankcase, where it mixes with blow-by gases. These gases are then directed through a PCV valve and routed back to the intake manifold. The PCV system consists of three main components: the PCV valve, a blow-by filter, and vacuum hoses that connect these components to the engine. The PCV valve is designed to restrict flow during high intake manifold vacuum conditions to maintain idle quality. However, in the event of abnormal operating conditions such as piston ring issues, the system allows excessive amounts of blow-by gases to flow back into the air cleaner via the crankcase vent tube, where they can be consumed through normal combustion.