> Missing hardware diagnostics
My iMac can’t enter hardware Diagnostics. When I hold the D key down during startup, it complains that it can’t load EFI/Driver/TestSupport.efi and I have to restart. How can I check its hardware?
Although normally easy to enter, it’s worth preparing your Mac carefully before holding the D key during startup to enter Diagnostics. If you have a firmware password enabled, turn that off first or it won’t work. Shut down and disconnect all peripherals apart from keyboard and mouse/ trackpad, which should be wired not wireless, any Ethernet cables, and external displays. If your Mac still won’t enter Diagnostics, shut down, ensure your Mac has a good wired or
Wi–Fi internet connection, and try again, this time with Opt and D held down together, for Remote Diagnostics.
The software for Diagnostics is hidden on your startup disk, and can get removed, for example if your Mac’s internal storage has been replaced. This is a surprisingly difficult issue to resolve: you should go to bit.ly/mac361 diagnose for advice, or Apple Support should talk you through it.