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Cannot start Apple Diagnostics

Hello, I can't start Apple Diagnostics on my MacBook Pro 16" 2019 (MacBookPro16,1)

I have Catalina 10.15.7 and encrypted SSD but I turned off every startup protection.

If I boot with D pressed, the Mac will reboot in 4 seconds after Apple logo appears, then appear the earth revolving and ends with -2104D error with triangle and exclamation mark referring to support.apple.com/mac/startup

The same happens if I boot with Option-D pressed.

I didn't find any reference to this error code.

Anyone can help me?

MacBook Pro 16″, macOS 10.15

Posted on Jan 3, 2021 10:20 AM

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Question marked as Top-ranking reply

Posted on Jan 3, 2021 7:27 PM

It means you have a networking issue of some sort.


Try a PRAM Reset. I don't like how the PRAM Reset is performed on the 2018+ Macs because I'm never sure it actually activates so I now use a Terminal command to clear the NVRAM/PRAM. Launch the Terminal app and use the following command:

sudo  nvram  -c


Press the "Return" key at the end of the line and you will be prompted to enter your admin password. You will not see any characters being typed on the screen so after you type your password press the "Return" key to submit the password.


Reboot your laptop and try using Option + D to access the online diagnostics. Don't let the Mac boot normally or it may modify the NVRAM again negating the PRAM reset you just performed.


If you still have problems try rebooting your router and waiting five minutes for the router to finish booting before you attempt diagnostic mode again.


If you still have issues, then try connecting the laptop directly to the router using an Ethernet cable and a USB-C to Ethernet Adapter so you have a faster more reliable connection and bypassing any possible WiFi issues. If your home Internet connection is very slow or you are using a hotspot, then it may not be adequate to boot to the online resources.

2 replies
Question marked as Top-ranking reply

Jan 3, 2021 7:27 PM in response to maiux

It means you have a networking issue of some sort.


Try a PRAM Reset. I don't like how the PRAM Reset is performed on the 2018+ Macs because I'm never sure it actually activates so I now use a Terminal command to clear the NVRAM/PRAM. Launch the Terminal app and use the following command:

sudo  nvram  -c


Press the "Return" key at the end of the line and you will be prompted to enter your admin password. You will not see any characters being typed on the screen so after you type your password press the "Return" key to submit the password.


Reboot your laptop and try using Option + D to access the online diagnostics. Don't let the Mac boot normally or it may modify the NVRAM again negating the PRAM reset you just performed.


If you still have problems try rebooting your router and waiting five minutes for the router to finish booting before you attempt diagnostic mode again.


If you still have issues, then try connecting the laptop directly to the router using an Ethernet cable and a USB-C to Ethernet Adapter so you have a faster more reliable connection and bypassing any possible WiFi issues. If your home Internet connection is very slow or you are using a hotspot, then it may not be adequate to boot to the online resources.

Jan 3, 2021 9:18 PM in response to HWTech

Many thanks. It turned out that was a network issue: I tried first from an iMac and got the same error, then I used another internet connection (an hotspot) and I got the hardware test running. So I rebooted my router and now works also with my home ISP. I'd think by myself that could be a network issue... but many thanks!

Cannot start Apple Diagnostics

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