They definitely can. The Chevy volt complies to the standard, but anything outside (ie to do with the battery diagnostics, or electric propulsion system) is behind a completely different protocol where most normal readers won't read.

Considering how every company is trying to paywall everything, I don't doubt they'll continue to push the "limit" further and further from any standard.

Yea, this has been an issue for 20 years, at least.

Manufacturers make it difficult as possible to retrieve any more than basic codes.

It's the constant cat-and-mouse game, and why I bought a very expensive code reader 15 years ago.

My friend, look up dodges asinine "security" gateway.

In some models you have to strip the dash to remove the entire head unit to get to the two extra plugs, not to mention having to have a compatible scan tool - $$$$

Man people on the Internet need to not engage with cars as much, they're clearly ignorant about them and have single instance counterpoints that clearly negate the fact you've put out there.

I swear by my OBD2 readouts, and my friends think I'm a wizard with a thousand dollar tool, rather than a dingus with a dongle, when I tell them what's wrong with their vehicles.

I can't believe you're being dumped on for having a fact about the industry