How do you know when the PCV valve is bad?

You can tell a PCV (Positive Crankcase Ventilation) valve is bad if you notice symptoms such as increased oil consumption, engine misfires, or rough idling. Additionally, if you see excessive engine oil leaks or a check engine light indicating a problem with the emissions system, it may signal a malfunctioning PCV valve. A simple test involves shaking the valve; if you hear a rattle, it's functioning properly, but if it doesn’t, it likely needs replacement.