What would a code PO442 mean on a 2006 Hyundai sonata

On a Hyundai it means that the catalyst is showing as inefficient. Now this usually means that the catalyst is going bad but you can try some catalytic converter cleaner, if it works then the code will stay gone after you clear it from the computer. But if it comes back then your in for an expensive repair. Have you considered getting rid of the vehicle? It is an 06 and a Hyundai with problems. They are only going to be more of them and more expensive as time goes on.