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'