The DMCA is the most relevant law here... and it's less what a court ruled and more what the Librarian of Congress says every 3 years. DMCA says every 3 year they have to issue (or extend for another 3) any exceptions to the law... The exception they've been offering for almost a decade now relevant to jailbreak is that the jailbreaking of smartphones is legal "where circumvention is accomplished for the sole purpose of enabling interoperability of [lawfully obtained software] applications with computer programs on the telephone handset." They've extended that to tablets and other similar devices since the original ruling. But more relevant would be- If what they're doing was writing their own control code to make the car faster this would probably be ok as "lawful modification" If what they're doing is providing a hack they gives your car unpaid-to-tesla access to the existing Boost or P code, possibly not so legal especially if/when Tesla encrypts the canbus content. That is not quite the case... you can't legally "void" a new car warranty other than for a salvage title on the car. You can deny coverage for any issue specifically caused by an aftermarket part, but anything related to aftermarket parts must remain covered by the manufacturer. So for example if you put aftermarket coilovers on the car and some other part of the suspension fails they can reasonably blame the coilovers for- no coverage for that. But they still have to fix your radio if it stops working.