Check Engine Code _ P0300 & P0421
 

Had my '03 Mazda Protoge (61k) checked for check engine light. Car seems to run fine, but was told the ignition coils and plugs need replaced before they will check/replace the cat converter (under warranty). Would car run okay if the ignition coils were needing replaced? Any way to test them first?

Coils wear out over time and produce less spark and don't burn all the fuel resulting in converter overheating and failure. It can seem to run fine but run rich. 60k is a bit low mileage for them to be bad but it could happen.