A recent NPR story exclaims that “copyright law makes it illegal to repair [farm] machinery run by software.” (DIY Tractor Repair Runs Afoul Of Copyright Law). WIRED essentially ran this same article a few months ago (We Can't Let John Deere Destroy the Very Idea of Ownership). Both authors make some good points, but both also overstate the facts to make their case. The Digital Millennium Copyright Act (DMCA) does grant John Deere (and other ag equipment manufacturers) the ability to prevent tampering with their proprietary software--such as the engine ECU--but contrary to the NPR article’s premise, normal maintenance and repairs do not run afoul of the law.
Farmers can still change the oil, replace parts, and service their equipment without breaking the law. But hack into the software to change how the engine runs or bypass emission controls and its a different story. As I stated in my prior response, John Deere does not own your tractor, just the software. However, it is worth debating whether farmers should have the right to tinker with how their machines operate.
For now, don't blame John Deere for using the DMCA to protect its technology investment. Apple does the same thing.