2018 MacBook Pro Target Display Mode Not Working

Solved on 2018 MBP 13" with TouchBar to mid-2011 iMac 27" and late-2013 iMac 21.5". Using the Apple Thunderbolt cable, my iMacs easily switch Target Display Modes with each other .. just beautiful. But even with the Apple USB-C to Thunderbolt adapter and the same TB-to-TB cable, from 2018 MBP to 2013 iMac worked only sometimes and often did the flickering deal. To the 2011 iMac, all I got was a black screen on the iMac. Finally I remembered my company had given me a Belkin dock which I don't use since the MBP can drive 3 external displays by itself. Using the dock, I connected my MBP to the dock with a USB-C to USB-C cable. Then plugged in the USB-C to TB adapter to the second USB-C port on the dock. Plugged in the TB to TB cable to the adapter. Now both iMacs go into TDM easily and stay connected with no flicker at all. MBP runs High Sierra (I cannot update to Mojave yet, since it breaks some company proprietary apps), 2011 27" iMac runs High Sierra and 2013 iMac runs Mojave.

This is the dock

https://www.bestbuy.com/site/belkin-thunderbolt-3-express-dock-hd-silver/5947892.p?skuId=5947892&ref=212&loc=1&extStoreId=1501&ref=212&loc=1&gclsrc=aw.ds&&gclid=EAIaIQobChMI9ueqgJC94AIVWR-tBh0CGwL1EAQYASABEgK_i_D_BwE

I had to upgrade my 2018 15" MBP to Mojave for the iMac TDM to work.

I had the same problem. It ended up that my third party keyboard did not transfer the command properly. I dug out my old bluetooth keyboard (that came with my iMac) and it worked. -- Good luck!

SIDE NOTE: I think Mojave needs to be upgraded to recognize when an additional device (monitor/pc) is attached and ask the user how they want to proceed. As it is, I have to hit CMD-F2 every time I start or wake my MBP, which means I have keep my old iMac keyboard and track pad on my desk for that sole purpose.

My Story:

Late 2012 iMac (was running Sierra)

MacBook 2017 (not Pro)

Was so happy when I found out my iMac was capable of TDM.

Immediately forked out $90 for the two cables (tb3->tb2) and the (tb1->tb1), originals from Apple.

When I tried it according to the description i got a notification on my MacBook that thunderbolt devices are not supported.

Of course Apple for some reason chose not to support tb3 on the Macbooks from 2017, only a standard USB-C connector sans tb3 (not been watching the WWDC's since Steve passed and just expected tb3 to be on all new mac products).

Since then I purchased a new 13" MacBook Pro (2018) so that I would be able to hook up the old iMac (and will be selling my MacBook (2017)).

Getting this to work with the new MacBook Pro was a PITA, this is what I ended up doing:

• Installed latest version of Mojave (10.14.5) on both the iMac and the MacBook Pro (2018)
• Dug up the original iMac Bluetooth keyboard and connected it
• Logged Off the iMac
• Logged On the MacBook Pro (2018)
• On the iMac pressed Cmd & Fn & F2 (even though keyboard is set to use Function Keys!)

In retrospect I guess installing Mojave on the iMac was unnecessary.

If it doesn't work right away, keep pressing Cmd & F2 or Cmd, Fn & F2 at the log in screen on the iMac.

Good Luck!

I had a customer who has two Mac computers

• MacBook Pro (15-inch, 2018) - Mojave 10.14.6*

•iMac (27 inch, Late 2013) - Mojave 10.14.6*

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STEPS:

1. I kept the iMac on the login screen (if your iMac is logged in, please log them out.) By Pressing on the apple logo and clicking on the last option being "Log out ..."
2. on the MacBook Pro this time have them logged in (admin user) (which was the only user)
3. keep in mind the cable has to be connected to both Macs
4. and now to focus on the the iMac you basically press ----> CMD F2 > and it basically starts TDM

so now you see it as the iMac being the display as it isn't logged into a user and the MacBook Pro being the main Mac where it basically as would have the content viewable on the iMac

_____________________________________________________

I am not sure if it was supposed to be this way now whether it may be with Mojave or with other OS

but this certainly helped me. and I advise you try this as the very first step once you've done all other TS

I had to update to Mojave and it worked. Fingers crossed that Apple provides a fix for High Sierra because we are not ready to upgrade to Mojave. Tested on the same 2018 MBP.

Been having the same frustrating issue for months now. Worked fine until I got this new MBP in Sept 2018.

I've found that when I log out of my user and back in on the macbook pro it works again every time, until it doesn't again. Seems to be a problem with the Macbook Pro, maybe the graphics card?

System:

MacBook Pro 15in 2018

macOS Mojave 10.14.5

2.9 GHx Intel Core i9

Intel UHD Graphics 630 1536 MB

iMac 27in late 2012

macOS Mojave 10.14.5

3.4 GHz Intel Core i7

NVIDIA GeForce GTX 680MX 2 GB

Yes. I have 2018 15" MBP with touchbar connected to mid-2011 27" iMac. Had problems until I realized my old 3rd party keyboard was not recognizing keyboard strokes CMD F2 until I went back to original keyboard. This may or may not be your issue. It's crazy that there are multiple ways for this configuration to fail, but it may help to know someone else has figured it out -- good luck!

This is a long thread, but you may find your solution. There are multiple solutions that people found for their setup. For me, I also have the mid-2011 27" iMac. I use it with my 2018 MBP with touchbar. My solution involved going back to my original keyboard -- not using my third party keyboard which did not recognize the key commands. But I now have to have that keyboard sitting on my desktop for the sole purpose of using the iMac monitor. Apple should upgrade the OS to auto-detect connected devices, ask what you want to happen, then remember the setup.

Did not solve the problem for me. 2018 MBP 15 with mid 2011 27" iMac, using

thunderbolt on iMac to thunderbolt on USB-C docking station on MBP.

Just upgraded to mojave 10.14.2. My iMac (high sierra) does nothing. Doesn't seem to

recognize key strokes at all. Tried all the suggestions. Original

bluetooth keyboard no longer works. Have McCally wired replacement with

identical mac keyboard. Tried original anyway. Nothing. Aargh!

and the list of "if it does not work" from the article are all does not apply?

If Command-F2 doesn't work

If your iMac doesn't switch to Target Display Mode when you press Command-F2, check these things:

• Make sure that the iMac you're trying to use as a display supports Target Display Mode. 
• Target Display Mode works only when your primary Mac is logged in to a macOS user account. For example, if your first Mac is at the FileVault login screen, pressing Command-F2 on your iMac does not enable Target Display Mode. You must first log in to your Mac (using a regular display, if necessary) before you can use an iMac in Target Display Mode.
• Make sure that you're pressing Command-F2 on the keyboard that's connected to the iMac you want to use as a display.
• In Keyboard System Preferences, if the checkbox is enabled for "Use all F1, F2, etc. keys as standard function keys," the key combination changes to Command-Fn-F2.
• Make sure that your Mini DisplayPort or Thunderbolt cable is connected to both computers.
• If you're currently logged in on the iMac you want to use as a display, try logging out to return to the login window. Then press Command-F2 again.
• Some older Apple keyboards and third-party keyboards might not allow Command-F2 to toggle display modes. If this happens, use the keyboard that came with your iMac to toggle Target Display Mode on and off. 
• If your iMac is currently started up in Windows, it won't enter Target Display Mode. Target Display Mode isn't supported in Boot Camp.

I have Mojave 14.3 on both a brand new MBP 2018 and a late-2012 iMac. I just got the needed TB2-TB3 adaptor and when I plug the two machines in and hit CMD-F2 on the iMAc the screen goes black and will not come back until I unplug the TB cable from it. Mojave has not solved anything in my personal experience. Glad it did for many, but this is frustrating, given I contacted support and read all the official apple pages on this prior to buying the cables and it seemed it would be fine.

Has anyone else had luck using the most recent Mojave version, 14.3?

No idea, as I only have the one MBP. My last one was a 2008 model that died years ago. BUT updated to add that while on the phone with a USELESS tech support person today it worked. Maybe it was her screen-sharing with me that pushed it over the edge? So random.

one note: on my mac, despite having my Function keys set to their F1, F2, etc. setting i STILL need to hit CMD+FN+F2. CMD+F2 alone does nothing. AND I need to hold the three keys down for about a second for it to work. I'm still not convinced this is going to work reliably going forward, but I'm happy for today at least.

Hi katbay, Thanks for advice! I have tried with Mac USB and BT Keyboards. They are the same ones that used to work for connecting Target display for 2+ years.

It is good to know that you have similar setup. I spoke to tech at the Apple Store, who told me they were having trouble with this particular model of MBP - am unsure if they meant Radeon GPU or just the 2018 model in general.

Thanks again.

I have a iMAC (27-inch, mid 2011) runs on macOS High Sierra version 10.13.6 and MacBook Pro (15-inch, 2018) runs on macOS Mojave 10.14.3. and connects the two using Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter. I could report that the target display mode is now working. I am so happy that Apple listened and fixed the problem. THANK YOU APPLE. You are the best.