KTuner.com

I just installed the stage 1 map on my 2021 NXS and got 4 codes after the initial install. Did the process of clearing outlined in the instructions but was left with 2 codes that will not go away even after multiple clearing attempts. Codes are p04a0 and p0476 which have to do with the back pressure modules. These codes were not present before installation of the tune. Other relevant info is that the car has a Fabspeed catback and the check engine light isn't on even with codes still showing. I've driven the car and everything operates as normal.

Any else have this issue or advice on how to resolve or if it's actually an issue?

You must have had some misunderstanding about the product, which has been announced very clearly. We do not disable error codes in the included stage 1 tunes and have never mentioned the ability to clear codes related to the exhaust valves being removed or disconnected. If you have any other questions refer to Science of Speed's release materials.