So I took my truck to my mechanic today to check why my check engine light came on, they said that the Catalytic converter was bad. I told them that the car dealership that I bought this truck from replaced that. They told me to contact the dealership and I did. Have an appointment in the morning to have them check it also. Now I need to know( what could be causing the Catalytic Converter to be going bad? ) My mechanic didn't check for the problem so I will have the dealership do that. any Ideas on what could cause this problem?