https://www.theverge.com/2018/10/4/17938820/apple-macbook-pro-imac-pro-third-party-repair-lock-out-software

Apple is reportedly using new proprietary software diagnostic tools to repair MacBook Pros and iMac Pros that, if not used on key part repairs, will result in an “inoperative system and an incomplete repair,” reads a document distributed to Apple’s Authorized Service Providers last month. A copy of the document was obtained by MacRumors and Motherboard today, both of which reported on the contents of the document and the apparent implications on third-party repair services.

It would seem that, without the proprietary software, third-party repair services will not be able to fix MacBook Pros that suffer from issues with the display assembly, the logic board, the keyboard and trackpad, and the Touch ID board, according to Motherboard. For iMac Pros, the lock will engage if you replace the logic board or flash storage. The computer won’t be usable again until Apple Service Toolkit 2, the name of the diagnostic tool, is used by a member of the company’s Authorized Service Provider program.