Apple’s security-focused T2 chip, which is found in the newest MacBook Pro, MacBook Air, Mac mini and iMac Pro, is not just a co-processor. The chip is the secret to many of Apple’s newest and most advanced features. But that's not all about it. The T2 chip is, in fact, a mechanism that allows Apple to lock down its devices from third-party repairs.
Apple introduced the T2 chip with the iMac Pro last year. The chip is a co-processor, and a hardware component necessary for new features like "Hey Siri" and Touch ID. However, Apple has now confirmed that the T2 chip also performs a series of diagnostics whenever certain component has been changed. And if it detects any unauthorized hardware, it bricks the whole device making it an inoperative system.
According to the official Apple document, the replacement hardware must be issued by the company's Authorized Service Provider (ASP). Also, after repairing, it needs to run a software diagnostics tool known as the AST 2 System Configuration suite, that only ASP centers or Apple Store have access to. So theoretically, you no more can repair or rebuild portions of the newest Apple devices on your own.
The parts affected include the display assembly, logic board, top case, and Touch ID board for the MacBook Pro, and the logic board and flash storage on the iMac Pro. The same applies to the newly released MacBook Air and Mac mini as well. However, Apple didn't mention if a technician needs to run the AST 2 System Configuration suite only after replacement of the listed parts, or after every single repairing work. If latter be the case, the DIY type of owners, and repair shops not in the Apple network are out of luck.
While this could be a step to ensure that Apple products get the best possible service, one can also see this as an attempt to grab more market share from the third-party repair services. Apple knows what it's doing, but make sure you take your Apple devices to ASP for repairs, or risk bricking.