I once had a car where I had to disconnect the battery to clear the check-engine light so it would pass a state inspection.

That usually doesn't work anymore as mechanics can tell that you've done that when hooking up the ODBII port.

I recently noted in my OBD2 scanner that some vehicles support the measure of miles since check engine lights were cleared or something to that extent. It made me ponder at some point in the future there is going to be regulation mandating that to pass an emissions test you must pull up to the test station with a minimal threshold mileage on the car to vet no check engine lights have tripped in that interval.

That's already a thing. Many sensors will be in 'learn mode' and you can't pass emissions until they are fully active.

> Do some vehicle manufacturers just put insane constraints on the drive cycle monitors?

Yes. Combine with the fact some only pass after certain conditions (eg. over 3000 revs for 10 mins, or idle for 5 mins, or only after 3 starts, only when the outdoor temperature is within this range, etc). Sometimes those conditions aren't stated in the manuals.

That makes the checks passing seem more like a random process and driving more will usually make them pass, eventually.

And drivers without a code reader won't know when it has passed, so they are usually instructed by mechanics to drive a long way to be sure before taking it in for a test (don't want to have to reschedule the test just because you didn't drive it enough).

And some jurisdictions will pass some “not ready” codes because a proper cycle may not happen for months.

A code reader really pays off sometimes to reset everything :)

There is a drive cycle set of requirements and it’s usually possible to clear them in under 20 miles. Trying to figure which part of the cycle isn’t accomplished yet is the challenge. I’ve chased it down on my wife’s Honda when we were trying to get it to go “Ready” the same afternoon. Usually just not doing anything unusual for a day or so of normal use is enough, but you can often query the OBD2 system to get the portion of the cycle that’s not yet complete. Just doing a long highway drive isn’t going to do more than a moderate highway drive already did.

That seems reasonable since anyone could clear and tune an engine with minimum effort to pass emissions without a history requirement.