Hi... I have an 07 GT with Mac long tubes, mac off road pro-chamber, and cervinis side exhaust, SCT 3 tuner, I got the "check engine code" P0420 im guessing it has to do with the O2 sensors??? Can someone help? Thanks in advance!

 

im pretty sure its a cat prob, your tuner should be able to cut off the o2 sensors for the cat or a custom tune will do it, or a diablosport predator i know will disable them

 

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Look in the book that came with your tuner. It lists all the trouble codes. The exact code means:

Catalyst System Efficiency Below Threshold (Bank 1)

So, yes, cat problem