A P0420 or P0430 code, a rattle from a broken substrate or a converter that has been overheated to the point of melting are the usual reasons to replace one.
Converters are certified for a specific engine family and emissions standard, and a federal converter cannot legally replace a California-certified unit on a California vehicle. Substrate loading and the position of the oxygen sensor bosses differ between applications even when the pipe shape matches. Replacing a converter without finding the rich condition or the oil consumption that killed it is a guaranteed repeat failure.
Listings state the engine, the certification and whether the unit is direct-fit. Diagnose the upstream cause before ordering, and check for a stored misfire or a coolant leak into the exhaust.
