i do as directing pressing D key during power up.
i get black screen with error messages.
any other way to run diagnostic tool?
iMac 21.5″, macOS 10.15
Switch to Hardware Test, as your Mac is too old for Diagnostics.
How to use Apple Hardware Test on your Mac - Apple Support
You might have to scrounge a copy of it.
As MrHoffman has mentioned, your Mac is too old to run Apple Diagnostics. You would have to run the Apple Hardware Test instead. This typically came on one of the original installation discs that came with the Mac.
Which exact model is your iMac that you are trying to run Apple Diagnostics on? What error messages are you seeing?
Late 2012 iMac with Catalina 10.15.7
black screen with
Error: 0x800000000000003, Can’t load ‘EFI/drivers/TestSupport.efi’
Status: 0x00000003
Can’t start apple diagnostic on intel iMac.
