imho The catalyst efficiency will suffer when the engine is mafunctioning. Even if it "feels" like it's running ok, there is an issue if p0420 sets, repair the issue before replacing the cat.So I have a 2012 Chevy Cruze Lt 1.4 I'm having trouble with this code I replaced the O2 sensors I replaced the front catalytic converter and the rear catalytic converter I totally don't know what's wrong with my car when I went to a local mechanic he said it was my front catalytic converter I replaced it but the check engine light kept coming on with that code GM they told me that it was my rear catalytic converter said they saw a crack near my flex pipe but it didn't penetrate to do any damageb from what I saw once I replaced it can anybody give me any type of help I really don't know what I should do my check engine light just keeps coming on?
Make sure that the cat you received from the local mechanic is a GM GENUINE catalytic converter!!! Aftermarket catalytic convertors will not work on the 1.4 engine and will set a p0420. Even with the engine performing well, p0420 will still set eventually with a non GM part.
Ask for your original cat back, it may still be useable if you received a non-GM converter during the repair.
Is there a reputable Chevy dealer repair shop known for diagnostic excellence in your area? or get 2nd opinion from a top notch independent mechanic...
I am not a mechanic and other members on this forum will be much better to help you with this... @JLL et al. But I have enough experience with our 2 cruzes to know that a p0420 should not be a reason to automaticly replace the $900 catalytic converter without chasing down the underlying engine issues first.
If I am understanding... without knowing what troubleshooting the mechanic performed, but replaced both cats to solve a p0420?? Look upstream 1st to solve cat probs.
Of course it is also possible that the cat was indeed dead...
Too many words and hope you have success finding an answer.