In most states (all?) this happens thru OBD II, so not a real test, with tons of exemptions depending on car weight/engine type/age.

This https://www.wep-inc.com/inspection-maintenance-programs/texa... is hilarious. You arent testing car emissions, you are reading car computer self report.

In EU, NZ/AU and probably many more places Tailpipe gas emissions test is routine. There are even mobile units with portable Emissions measurement systems. Meanwhile even California doesnt mandate tailpipe tests :o

I didn't say anything about testing. I've never heard of anyone doing emissions testing on tractors after it leaves the factory. I said that the EPA will get mad if someone changes the emissions. The EPA has already hinted that making it possible for random people to violate emissions by changes the software will be a bad thing. Not sure how this will turn out in court and laws, but it is a factor.

When I press people on what parts of their tractors they can't do now it generally comes down to something that would make the tractor not pass emissions if it was tested. Parts and computer test equipment is readily available.

This is precisely my point. Rest of the world tests, they test actual exhaust emissions, and there are regulations and penalties.

US on the other hand legislated computer DRM "for engines" because its cheaper/faster, anything beyond is a super special case. My favorite is actual tailpipe test commercial trucks must pass in NY - they test opacity of gas aka "is the smoke visible?" :o and look for physical presence of all mandated emission hardware for that model/year/exemption status. All of that theater instead of using proper exhaust gas analyzers.

>Parts and computer test equipment is readily available.

Can you download standalone John Deere service software? or did you mean signing up for their paid SAAS package?

They do for older cars.

Its the other way around. Older/weirder stuff is usually fully exempted.