While I had my 09 GT convertible I contributed regularly to this forum. Now that I have a 2014 GT coupe, I'm the one in need of direction. I just had installed a set of GT500 axle backs because the Roushs that came with the car were waay too loud. I also had a check engine light that was throwing codes P0420, P0430. This indicated a Cat converter prob. I reset them twice but they returned quickly. While my mechanic changed out the axle backs I had him research the codes. Here's the surprise- I got Cat eliminator pipes instead of actual Cats. The Oxygen sensors screw right into the pipes but those codes will never go away. Rock Auto has Cats them for approx $135 each which ain't too bad. I asked the mechanic how much for him to get the Cats and install them. He told me that the car normally has two Cats on each side and the price would be high. I did a little research and got the attached image off Tasca Parts and I'm only seeing two Cats (#1 & #2). I think that he's mistaking the resonators (around #6 & #7) as another set. Additionally, per the other image, I'm only seeing two Oxygen sensors and he told me a grand total of four. He advises to leave it as is and live with the check engine light. I am in South Carolina which has no inspection but it's technically illegal and I would like to correct it. Is he correct or not? TIA.