There is a standard connector which existed before big screens landed in cars, the OBD2 connector. Dongles are cheap and you can read the output from your phone or computer. Some dongles support bluetooth. The connector is mandated in some markets and I guess that makes it less interesting to add a redundant interface inside of the car. It's fun to try if you're interested. Manufacturers can extend the error codes IIRC.
Tesla has a service mode on the display through which you can scan the car for faults, run a battery test, ... It is password protected but the password is publicly available.
ALDL was proprietary to GM kind of like apple and their connector tomfoolery. In 1990-something CARB probably didn't want to buy all the different diagnostic tools so they said if you want to drive in California your car needs OBD-II. Now, I can check and clear codes on any modern car with a $35 tool.
Interesting fact. OBDII is a CARB requirement, so it’s tied to cars that must meet emissions standards. This is why Teslas don’t need to include one (ands it likely other manufacturers will stop including them in their electric models at some point as well). No emissions systems to check means no need for an OBDII port.
Bingo! You can get a BT adapter for $7 on eBay. Torque is the absolute killer app. I'm stunned something so complete and customizable is free, a few bucks for the full version. I suck at mechanics, but that has saved my butt a time or two.
If you own a car that was made in the last several decades, it has the OBDII connector under the steering wheel and openly accessible. You just plug the adapter in and connect to your phone. The adapter and app are every bit as important to me as a jack, lug wrench and tire pump. No one should be without for a measly $20.
My wife's car occasionally throws an error that kills the cruise control. She can clear the error code while I'm driving! If you have ever had a mysterious check engine light, you can see exactly what it means.
Yeah, particularly it costs more, which you would need customers to want to pay for. If those same customers can just get an OBD-2 connector for a fraction of the upcharge, that's not gonna work out...