There was the DeCSS case, other than Sony's autorun CDs I think that would be the most trivial "DRM" but was still ruled a violation to circumvent.
Auto manufacturers, along with printer manufacturers, are already using IP in the on board diagnostics and printer cartridges to claim copyright violations when people adjust or replace parts "without authorisation."
Because the CSS code was there for the purpose of preventing unauthorized duplication of content, not to restrict people's ability to control the functioning of their DVD players.
Regarding printer cartridges, there have already been court rulings [1] that have determined that "jailbreaking" them isn't a violation of the DMCA, making the distinction specifically on the basis of whether the the element of the product being protected is "creative" or "functional". So we already know from case law that the DMCA doesn't actually prohibit people from circumventing functional lock-outs.
Auto manufacturers, along with printer manufacturers, are already using IP in the on board diagnostics and printer cartridges to claim copyright violations when people adjust or replace parts "without authorisation."