My wifi drops when I plug in an external monitor through the thunderbolt port

This same problem appeared for me after months of using the exact same hardware and software setup (MacBook Pro 10,1 + Yosemite + 3rd part Thunderbolt display adapter + Dell monitor).

After trying 5 or 6 suggested fixes, I found that disabling my AirPort Express's AirPlay feature fixed the problem. Obviously this makes it hard to use AirPlay :-(

rodsab wrote:

Try this, go to system preferences then network preferences. Select Thunderbolt Ethernet and "make service inactive" (click sprocket icon at the bottom)

This improved my WiFi connection speed. My thought being that Thunderbolt is a multipurpose port also used for ethernet and may be taking priority when it is plugged into any device. If you are using WiFi Thunderbolt ethernet is obviously not needed.

This tripled my speed on WiFi with a displayport monitor connected. I did not have this issue previously, but today I was using a different cable and my WiFi would not connect at all. After some troubleshooting I discovered that it was only when my 4K Dell displayport monitor was connected. I switched to a different cable where I could negotiate a WiFi connection, but my transfer speeds were about 1/3 of my actual bandwidth with heavy packet loss. After making the Thunderbolt Ethernet service inactive I ran another speed test and had full bandwidth available with no packet loss. This is a pretty messed up problem, Apple. I'm on a 2014 MacBook Pro maxed out running Yosemite 10.10.4.

Im sad to have to say that my Early 2015 MBP Retina 13" (running El Capitan) shows exactly the same problems when connection via HDMI to a ASUS VX24A - no wifi unless I'm in 720p - it supports up to 2560x1440 - main intention was to use it for graphics on the mac when at home!!!

Tried changing my Sky router from auto to both channels 1 and 11, no such luck there either 😟

Actually that did not fix the issue.

Finally figured out a way to make this work. Good news all you poor souls in torment 🙂. I covered my cable with some aluminium foil and voila wifi started to work. I had to adjust the foil so as to cover tightly the head of the mini DP, and form a sort of cone around the cable(away from the head).

First, changing the channel numbers from auto to 1 through 7 did not fix the issue for me. Changing the resolution also did not help. Taking the laptop max distance away from the monitor also did not help.

Configuration :

Macbook Pro 13 El Capitan

LG 27UD68

Verixon MI424WR router

StarTech.com 6 ft Mini DisplayPort to DisplayPort 1.2 Adapter Cable M/M

The root cause of this is indeed interference generated by the DP cable, in my opinion.

The reason why swithcing to channel 1 works for many is that using channel 1 causes the 5Ghz spectrum to come into play. However, this will help only if you have a router which support the dual bands of 2.5 and 5 Ghz. Mine supports only 2.5 Ghz. Fios quatum has dual band routers according to google.

Not sure why even apple DP cable gives this issue for some.

There you have the solution which worked for me. I wonder if I should try out a apple cable as well or just get a better router. Having aluminium foil sticking out next to MBP is not what I would like.

Well I tried all of your solutions guys but none worked for me...

My ISP don't let me change the channel of WiFi

* MacBook Air (Mid 2012)

* OS X El Capitan 10.11.5

* 3rd party HDMI adapter

* LG TV

The cable and TV works fine on non-Apple computers (both windows and Linux). Shame I have access to only one mac.

My complain is that everything was running fine last week, but since Sunday I've got the speed drop issue.

Any Idea?

Already tried to change resolution, unplug-plug, reset router (config blocked by ISP), deactivate Thunderbolt networking :-(

I fixed it by changing the wireless channel too. Option Click the wireless icon in task bar, then Window menu > scan and choose the Best 2.4Ghz recommended channel. In my case channel 2. Then changed the channel in my router's internet page which was 192.168.1.1 for me. Thanks for the thread. Still an issue in 2016. What a joke.

I have this same issue. Just bought a brand new 13" MacAir i7, Dell 28" S2817Q Monitor, and a Henge Dock. Excited evaporated with this unforeseen issue. +20mps drops to less than 4mps when plugging in monitor. Closed lid, in dock, out of dock, open lid, makes no difference. Is it a Thunderbolt thing? This is not a coincidence. C'mon Apple how 'bout a solution instead of a finger point!

I fixed it simply by changing the position of hardware on my desktop.

From mbp > lg4k > wifi router

To lg4k > mbp > wifi route

All hardware is on the same line, near the wall: so I think that display was stopping wifi signal before arrive to mbp.

I hope my magic helps someone.

Bye

I have been struggling with this problem for two days. Brand new MBP 2016 with touch bar. Top of the line 13".

Initially I was using an AUKEY vga hub with 4 usb ports. My wifi would drop to a crawl when the hub was underneath my dell monitor. Also, the monitor was jumping around and the Phase/Pixel Clock would not fix it so it wasn't jittery.

I resolved the problem a bit by moving the vga/usb hub to the opposite side of the desk away from the monitor. This allowed for internet access, but still not as fast as the speed without the hub plugged in.

Also, upon a low battery, when the computer tries to wake from sleep with this hub plugged in, the computer malfunctioned to a point where i could only see the pointer as well as notifications.

After a trip to the apple store (where i spent several years working, leading the sales floor) chatting with my good buddy who is now the genius admin, we determined that it could be a power management issue. Once the laptop had enough power, it was able to figure out its display settings and could view my desktop again.

MAINLY... to resolve this thread issue, I purchased a Belkin usb-c to vga. This adapter has no other use. It has no usb plugs nor does it have a usb-c input that may cause any interference. I now have a clear picture on my monitor and absolutely no wifi issues.

my opinion is that while the technology is suported for the usb-c to handle multiple tasks through one port, it can be overloaded and really hinder the performance of the computer. Try avoiding a hub if at all possible to test my theory.... worked for me, but now ill be carrying a bag of usb-c adapters.

This worked for me too!

Late 2013 Retina Mac Book Pro, Dell P2715Q @4k, and Ubiquiti Router.

This configuration had been working fine for the past few years, the issue just started today (-2 hours!!). Changed the router frequency to channel 1 and it came right.

Wifi was either dropping most packets or not connecting at all. Narrowed it down to the monitor connected with Thunderbolt/DisplayPort and then google found this post.

I had the exact same problem. Some how it started after I upgraded to the latest OS version. Tried everything and nothing worked. I thought it was my tv blocking the signals so tried to put the range extender, still no good. Came across this post and found changing a channel might fixed. I changed the channel from 6 to 2 and it started working. Now I can have monitor connected and still can access wifi/internet. So happy.🙂🙂🙂

Problem on old and New.

I had this problem om my 2011 early Macbook. It broke so I bought the new 2017 Macbook, the stupid one with only 4 USB 3.1 ports. One would think that they would have fix the problem in such a new and expensive computer. But no, it's still there.

Today I discovered that my WiFi drops whenever I plug in ANYTHING (except the charger) through the thunderbolt/usb 3.1 ports. I kinda makes make computer rather useless.

Here is a list of possible sources of interference. http://support.apple.com/kb/HT1365. See bullet 7 which relates to monitors.

I managed to fix it by changing wifi settings on my asus wifi-router. I have changed channel number to 1.

Same problem here.

BRand new mbp retina with apple thunderbolt to dvi adapter. Once i unplug the display wifi works good.

Very big issue for me.