In 1990 Ford couldn't turn off your Mustang because you plugged a TwEECer into the J3 port and screwed around with the tune. Best they could do was void your warranty and deny you further upgrades (i.e. tunes flashed as part of a recall or TSB).

These days unauthorized access tends to lose you effective use of the hardware you bought because the hardware requires software features to work and that software often unnecessarily phones home so if the OEM toggles a field in a DB somewhere you lose access to back up assist or whatever other fancy tech features that you a) paid for b) don't strictly need to have dependencies that phone home to work but do "because reasons".