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I’ve been struggling for a while now with a check engine light (CEL) on my 2021 C8 Corvette Z51 after installing a valved cat-back exhaust.
Here’s the situation:
2021 corvette z51 htc , performance exhaust
I’ve installed AFM simulators, and they seem to be working fine with no issues on that end.
The exhaust valves themselves are functioning normally — they open and close as they should.
I’ve performed the valve relearning process multiple times, but the CEL keeps coming back shortly after.
I’m attaching a few pictures from my OBD Launch Elite scanner showing the fault codes and data.
At this point, I’m just trying to figure out the root cause — is it a sensor-related issue, ECU adaptation problem, or something else that needs to be tuned out?
Any advice or experiences from other C8 owners who’ve dealt with this would be greatly appreciated.
relearn video link:
https://files.fm/u/n2jkhzmd86
Thanks in advance!
Last edited by shadowhtc; Aug 30, 2025 at 03:18 PM.
I had the same issue when I installed AFE on my 2022 Stingray and my fix was to a local dealer and they did the relearn and no more codes, I put the exhaust on my 25 ERay it had no codes, however I took to the same technician and had him do the relearn and no codes on my ERay
i have no issue with the AFM , simulators work just fine
what i am talking about the npp valves which works as intended when select tour it goes silent and my mod opened up , but still throws cel refer to pics above and video link of trying to do relearn,
I am having a similar relearn issue (Borla S-Type on '21 C8), check engine light being triggered by the passenger side AFM valve. My installer wants to install simulators on the AFM's to eliminate the issue. I'm curious, those of you that have installed simulators on your AFM valves, does the exhaust sound weird when the engine goes into cylinder deactivation but the AFM valves stay open (assuming I understand the operation of the AFM valves correctly)? Thank you in advance for your input.
Persistent CEL Valved Cat-Back – Need Advice
