Check Engine Code P0421

A code will never point to one item as needing replacement, it takes a diagnosis of the related systems to determine the fault. Here are some things to check for that code: A code P0421 may mean that one or more of the following has happened: * The catalytic converter is no longer functioning properly * An oxygen sensor is not reading (functioning) properly * A spark plug is fouled up

read it somewhere in the manual.timing belt i think.