macOS Sequoia 15.3 wont let me detect my second display

phaed2 wrote:

I tried everything, and it was this that seemed to trigger the monitor being detected again for me! It started with 15.4 and persisted with 15.5. I finally got it working today by completely unplugging the thunderbolt cable, turning it around and plugging it back in again (maybe it was just fully unplugging both ends rather than turning the cable around, I'll probably never know).

For context, I have a MacBook Pro 16 (2021), plugged into a Thunderbolt 3 Anker dock via single cable to provide power and monitor connection (4K monitor is connected to the dock via HDMI). After upgrading directly from Sonoma to Sequoia 15.4 my monitor was no longer detected. I upgraded through a couple of bugfix versions, before getting 15.5 today, and still no luck. I was having to plug the monitor into my MacBrook Pro directly via HDMI in order to get some work done... until today when I tried unplugging everything (only 1 TB3 cable and 1 HDMI cable), plugged the HDMI cable back into the dock, turned the TB3 cable around, and hey presto, the monitor came back to life.

Update: After my MacBook went into sleep mode overnight, it woke up this morning with no access to the external monitor. So back to square 1 for me... I'm not convinced there is a reliable fix for this until Apple fix the issue.

Hi, after trying out different cables, checking the connections, realized that just allowing about 30 - 40 seconds for the display to come up in the external monitor helped to resolve the issue in my case. The external monitor was keep trying to pick up the signal and saying "No signal found" and "Entering into Power save mode", after about 3 / 4 tries, the display started to come up with no issues. I've not used any of the commands recommended in this Forum as this is corporate laptop and I was not sure of my level of authorization in it.

sudo rm -rf /Library/Preferences/com.apple.windowserver.*

this is the fix. 15.5

Edit: fixed it by creating guest account.

external display showing up again

then Log off and go to your main account

For me what helped was this:

• Disconnect monitor
• Run these commands both:

sudo rm -rf /Library/Preferences/com.apple.windowserver.*
sudo rm -rf ~/Library/Preferences/ByHost/com.apple.windowserver.*

• Reboot
• Login
• Reconnect

close the mac. disconnect ALL cables (all!). close the monitor or just disconnect ALL its cables. wait 5 minutes. reconnect and boot all devices. worked for me and I had the exact same problem

I ended up buying new cables. HDMI to usb-c directly without using a docking station or adaptor, Reset NVRAM/PRAM and finally got it to work.

I managed to fix it. It was a combination of the discussed solutions in this thread.

• Disconnect the non working displays from usb c as well as power for some minutes
• Delete the library/preferences/byhost/apple.windowserver.displays.plist file
• Delete Trash

I repeated this procedure 3 times until each display works.

I too had the same issue. I rebooted a few times and still prevailed. I unplugged my thunderbolt hub where my displays are connected via HDMI and that still didn't work. It wasn't until when I pulled the HDMI cables and switched them that for some reason the displays detected again and all is well. Best of luck!

I waited until 15.3 because of all the reported issues with multiple monitors. For me, at least, there are still issues with 15.3. I have a MBP16 with 2 Apple Thunderbolt Monitors.

Both monitors work for me.

HOWEVER, I have to reboot every morning to get both monitors to work. When waking up from sleep, only one of the Thunderbolt monitors is recognized. Restart MBP and back to both Thunderbolts working. A pain but at least they work.

sangy987

User level:

Level 1

32 points

Feb 13, 2025 4:44 AM in response to WozaMAC

First, I ran this command:

sudo find / -name "*windowserver*" 2>/dev/null | tee ~/Desktop/windowserver_files.txt

Then I analyzed wherever the plist files are there.

Then this

sudo rm -rf /Library/Preferences/com.apple.windowserver.*

Then I rebooted. It worked for me. I upgraded to 15.3.1 hoping it would fix the issue but it did not.

My fix was surprisingly simple, that is I switched from a miniDisplayPort-USBC Cable to a HDMI-USBC cable.

Tried all the software fixes discussed to no avail, but this did the trick.

I can't believe after days of trying (with no success) all the fixes people posted on reddit and here, this is what worked for me...TURNING THE CABLE AROUND. Anyways, thank you so much.

shut it down and wait for 5 minutes having disconnected all cables. same for the monitor (disconnect everything)

Ya mon...worked! Connecting a different USB-C hub and both monitors were detected as normal.

Thanks bruh!