Infamous CEL need help

Hello RL I have been reading pages and pages on RL. There is sooo much useful information and gurus on here. Looks like some have moved on and other new gurus have taken their place. I need some help and so I am posting on the forum. So back story: 3rd owner, new to me car (and platform), serviced by reputable shop. C4S 03, has billy boat headers, cat delete and AWE exhaust ( i can verify this by parts being stamped and some paperwork/receipts). When I bought the car, I was told CEL is from passenger side post cat O2 sensor, swapped out for 300 for sensor and the labor. Car was then shipped and I received the car and CEL was on. I can�t recall the code but it was for a faulty O2 sensor (my mechanic looked it over). I tried to figure out what is wrong and then when I took a closer look it made sense. The cat delete is not the x pipe style. The precat O2 sensor on the driver side has the correct O2 sensor in the location, the post cat O2 sensor location was way down stream. It was in the location of the passenger side post cat O2 sensor plug. The same case was for the passenger side. The first shop thought they were swapping out the passenger post cat but the driver side post cat was the issue. My mechanic noted it as well. The O2 sensors were then correctly plugged in as they should be and I swapped out the bad O2 sensor. After 3 track events and couple thousand miles i have fault codes of P0420 and P0430. I don�t have cats. Car passed inspection as well. I am assuming car has tune for the exhaust work that was done in past. Ideas? I am thinking of looking at MAF, but don�t want to start off on some crazy hunt. It really does not make sense to me. I swapped out the pre cat O2 sensors as well. After that process I am hoping to either trouble shoot this with a small fix or just get rid of cat delete (does sound nice and car feels very strong) and get hi flo cats as I do track days. I�m worried that if the issue is not the cat delete and the light stays on after I get the hi flo cats. Trying to solve this without burning my resource kept for tires/pad/rotors/etc Thank you for reading and your helpful responses.

The P0420 and P0430 are related to CAT efficiency. Since you have a CAT delete, the O2 sensors are telling you that the CAT is operating below efficiency, which is to be expected since you have no CAT. Don't know how you solve the problem, unless you get some sport cats. I assume you have a tune that hopefully ignores the CAT efficiency and keeps the car in a correct tuning mode without running to rich or lean. However, that tune cannot make the P0420 and P0430 CEL from coming on. https://axleaddict.com/auto-repair/C...rs-For-Dummies

What DBjoe said. If you are running the stock tune, you need to install O2 sensor extenders on the post-cat sensors to fool the DME. If you are running a tune, I've heard those codes can be coded out. P0420 and 0430 have nothing to do with your O2 sensors. The sensors have their own codes. Not sure how your car passed smog with those codes though.

As others stated, you should be able to eliminate the CEL with a couple O2 sensor extenders, like so: https://www.fvd.net/us-en/FVD111LAMA...ividually.html I believe you can get these from local auto parts stores, they are referred to as spark plug non foulers https://www.napaonline.com/en/p/NDP7302444 (note: 14mm just used as an example, not sure what the correct size is)

I should have mentioned I have very long angled spacers in place. Can't remember their name but a thread on rennlist recommended them as they had success in past. Order of events 7/2017 o2 sensor code, changed out, light returned and then sorted out the connectors were swapped 3/18. CEL again pre cat sensors swapped out. Car was taken for emission testing 7/18 passed. CEL came back on after the emission testing. car must have a tune otherwise there is no way I would have passed emissions/OBD2 testing. That's what doesnt make sense. No cats on car, CEL for cat and it passed. I am assuming there is a tune. I did get a lead from someone. I will follow up on it. If it works i will post it here so others can find a solution versus skimming the internet for hours without a solution.

Update: I bought FVD O2 emulator and ran spacer with cat delete...no CEL. Went for inspection and they a visual...failed. I contacted SOUL performance Gaydos hooked me up at the glen with HJS 200CEL high cats and car passed. My deletes, extenders and emulator will be up for sale. Those deletes sounded amazing. I may dump the exhaust cans to lose weight. A huge Thank you to quadcammer and NYC993 for installing. Quadscammer also installed radiator manual fan switch.