The legislation has to be robust. No dice if the dongle is generic and $20 like OBD2 in cars, but that on top of that there's a per-manufacturer set of codes that only licensed dealers have access to the software to read those special codes.

The situation today is at least better than it used to be before OBDII. I much prefer using a scanner to get codes then having to count flashing lights. And back then you'd still have to pay a lot for the manufacturer's code reader. The only advantage was the ROM was small enough to disassemble and reflash with new features. I would not want to do that on a car made in 2026.

Most of the codes on a large tractor are j1939. You still want the manufacture database because it often says 'x sensor voltage out of range - check the wiring harness in some not obvious location'