[tpmoney]

The EPA has a document here https://www.epa.gov/sites/default/files/2020-12/documents/ta...

With a relevant paragraph on page 2

The site you linked mentions the carve out that the EPA has, but note that it requires both retaining or beating original behavior and requires extensive prod of that fact. A similar law affecting phone home circuits would almost certainly not find disabling the ability to phone home as in compliance.

[jibe]

The part of your post that made me curious was whether fuel mapping, or ECU swapping was illegal. It looks like it is in a grey area under Clean Air Act, but generally interpreted as legal as long as you aren't doing things to make your emissions worse.

[tpmoney]

At least as far as ECUs go, almost every after market ECU I’ve seen doesn’t control OBD II or the CEL (or does so very minimally) and is therefore immediately in violation of not conforming to the requirements to retain OEM level behavior. Fuel mapping is more grey, largely due to the ability of some OEM ECUs to be reflashed and thus retain OBD behavior.