2018 MacBook Pro Target Display Mode Not Working

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

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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

PS this was only ever an issue on the MBP 2018 15inch, which I have, tested it in the shop before the patch on the 13 inch and it worked, all fixed now on 10.14.1

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.

I'm experiencing the same issues, exactly as you described them. I contacted Apple Support and a ticket was created, and eventually escalated. I recommend you also contact support so the issue can be tracked.

Another user has reached out to me, stated that they've spoken to support, and that support is aware of the issue here: Daniel Storm on Twitter: "Anyone else with the new 2018 MBP having issues with Target Display Mode?"

I'm having the exact same issue with my new 2018 MacBook Pro 15" i9 and my late 2013 iMac as a target display. I've tested multiple apple thunderbolt adapters and thunderbolt cables but didn't work. I called Apple Support and the rep I spoke with was unaware of the issue and seemed to think it was specific to my computer, but I informed her of this thread. After a series of multiple tests and restarts and eventually an OS reinstall, I have the same result in target display- a flashing unstable screen on the iMac. For what it's worth, I connected my iMac to a 2015 MacBook Pro thunderbolt 2 and target display worked perfectly, so I know the issue is with the 2018 MacBook Pro. Very disappointing after spending a small fortune for this machine....

*UPDATE* I connected my 2018 Macbook Pro and my iMac 2015 to a belkin hub. Target Display Mode has been working for an hour. Honestly, I'm afraid to try the direct connection between my MCP and my iMac because I don't want to mess anything up right now. But somehow, the central belkin hub is helping out with the glitching problem. The iMac has been working in Target Display Mode flawlessly (for now). I'll try the direct connection between my MCP and my iMac later in the day.

Same issue. I was using Target Display Mode (TDM) with my MBAir to my 27-inch, Late 2012 iMac, and it worked fine. I bought a 13-inch 2018 MBP I was excited to use with my iMac in TDM to replace my MBAir. I plugged in my new MBP and just got a black screen. After many trips to Best Buy thinking it might be a faulty cord or adaptor, I ended up with what I think is the simplest solution - an Apple branded Thunderbolt II to USB-C adaptor and a Apple branded Thunderbolt II cable. With this set up the best results I get is an intermittent scrammed image fluxing between clear and scrammed (every 30 seconds or so). Sometimes if I wait long enough it will clear and the screen will look fine until I exit out, but when I boot back into TDM it starts the scrambling all over again. If the screen goes black and stays black I will need to exit out of TDM and then wait until the next day to attempt to try to get it to work again.

I called Apple Support they worked with me for two weeks and kept escalating my problem to higher and higher. Finally they said it would be a firmware update for both the iMac and the MBP and to look for it in upcoming software updates.

As of today Sept 19, 2018 there has been two software updates for the MBP and one for the iMac but nothing addressing the TDM issue.

I will be following this post to see what others say.

After tedium with Apple on-phone support it was clear this was going no where fast.

FIXED:

So, for a busy person, I spent way too long researching dongles and found a Sicotool USB-C dongle that has a mini display port in it - worth a try I say. And look at that.... At the same price as a Apple T3-T2 Adapter, this dongle does a marvellous job at getting a monitor signal from one of my 2018 15" MBP's T3 port to my late-2009 iMac's mini display port. I don't even have to faff with Target mode, it instantly finds it and got dual screen. The image is also perfect, better than what I had with my 2012 MBP (i.e., no faint ghosting etc).

Well done random Chinese dongle manufacturer - you've done what Apple can't do!

Possible work-around for most users here, is to launder the signal provided by your 2018 MacBook Pro through a ThunderBolt Hub. This seems to re-drive the signal, and make it conform in a way that the iMac can accept without issues.

I bought my 13" 2018 MacBook Pro when they first came out and have been frustrated with Target Display Mode for so long. Now I can also confirm, the 10.14.1 Beta fixes the problem. I only downloaded it on the MBP and now it is working as smooth as butter. I am VERY VERY VERY VERY HAPPY RIGHT NOW! I will not go through the details of downloading the beta others have already done that in this forum - this is a good day. I hope the person that worked on the fix will be able to reads these very appreciative comments.

I can confirm after testing all new machines and OS at the Apple store that the only effected machine is the MBP 15in running Mojave, the 13inc worked fine with the adapters, hopefully 10.14.1 update fixes it as people have mentioned that the Beta3 of 10.14.1 has fixed the issue, and we can all get back to using our iMac as a second screen

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