Is My Catalytic Convertor Bad? We get this question sometimes. If your vehicle is exhibiting symptoms such as a Strong Sulfur Smell or you are losing Fuel Mileage, it is possible that your CATALYTIC CONVERTOR is bad. It takes Specialized equipment to test your vehicles Catalytic Convertor properly. Also, another symptom you could notice is your vehicle has low power and this could from a clogged Catalytic Convertor. Your Check Engine Light may be on with a P0420 and/or P0430 code in the ECM. If your vehicle has any of these issues give us a call and we will be happy to diagnose your vehicle and let you know what needs to be done to fix it