I just had my two main cats replaced under warranty...both were clogged up apparently and causing all kinds of problems with check engine lights blaming the O2 sensors. Check your cars in service date to determine if you truly are out of emissions warranty. I thought I was but found out otherwise...saved me a ton of money.
If its the secondary set of cats on the car then I wiould just bypass them. They are not needed as far as i am concerned.
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