Lexus 12204-20040 Valve Sub-Assy, Ventilation

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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.