Just throw an O2 extender on the post cat oxygen sensor. Done deal.
Im surprised you got the CEL still. Many of us run JDL catted headers, myself included without trouble. I know there have been issues with HKS cats for some as well.

 

I've cleared that code by disconnecting the battery and restarting the car that way. Are you on stock overpipe/frontpipe as well?

If you're not ready for a tune getting an o2 extender might help to trick the ecu.

 

^this.

Seen a few examples where they forget to disconnect the battery which causes the sensors to readjust.

 

x3

O2 extender time

 

So to begin, I own a 2014 Scion Frs and had the ft86speed factory uel headers installed and used for about 15k - 20k miles. Since I acquired a 2022 Gr86, I decided to swap the headers out from my Frs.

My thought was that I would not get CEL's due to the fact that the Headers have a hi-flow cat. Another thing to mention is I also have swapped the whole exhaust from header back so now the only cat I have is the one on the headers.

Ft86speed factory catted uel header
Manzo Overpipe/Frontpipe
Mxp Comp-Rs Catback

Before I installed the headers, I looked at the cat and it did not seem to be clogged or chipped/broken in any way. Looks brand new but then again I don't know what to look for in that.

Any suggestions? I cleared the CEL and it came back the next day. Cleared it again and will drive and wait.

I don't have a tune yet I am planning on getting the tune within the month. Thanks

I also have a header with high flow cat and would get a CEL after a few hundred miles driving. Put a defouler spacer on the 02 sensor and you will be fine. The front pipe cat is downstream so it won't affect your CEL. My single cat in the header works well with a dual resonated front pipe--no smell and no extra noise. As TRU said, some of the high flow cat headers cause a CEL on the Gen2 (HKS, apparently the ft86speed, etc.).