2019 15" MacBook Pro Throttling Gigabit Ethernet Speed

Hi Everyone,

I recently moved into a new house and I’m now able to have a ethernet connection to my 2019 15" MacBook Pro (running macOS Monterey 12.3) that I use for work. I also have a gigabit internet plan, so I was very excited to get the improved network speeds. However, despite a wide array of permutations of ethernet dongles, ethernet cables, and testing connections with other devices, I’m left that the issue lies solely with my 2019 MacBook Pro and I’m looking for some assistance or confirmation of that theory.

I have confirmed that the dongle and ethernet cable I am using are both capable of handling gigabit speeds by testing on other devices. I have seen gigabit speeds on my wife’s 2017 15" MacBook Pro and my Steam Deck using the exact same cable and dongle. I also confirmed my wife’s MBP was using the same driver as my MBP.

After thoroughly diving into a rabbit hole about MacBook ethernet drivers, I tried testing my MacBook Pro with a 2.5Gbps ethernet dongle which utilizes a different RealTek chip internally as well as a different driver in macOS and unfortunately saw the same Speedtest results as my original dongle.

My current theory is that the issue lies in my MBP’s thunderbolt busses being thermally throttled because my machine idles around 72ºC and near constantly has its fans running. The only other computer I saw throttled ethernet speeds on was my wife’s 2018 MacBook Air, which she has mostly stopped using because of thermal throttling (no clue what the temps are, but she had similar issues with the fan running constantly).

So having laid all that out, I’m hoping to either get more ideas for troubleshooting what my issue may be or a confirmation that I’m not the only person who is seeing this issue and that I likely cannot remedy it without storing my MBP in a refrigerator.

I’ve been trying to hold off buying a desktop M1 Mac for a while now because there still is not one on the market that meets my high-level purchase criteria (<$2k, 32GB Memory, can utilize 3 external displays), but it seems like every day now I’m inching closer to buying a Mac Studio…

Thanks for your time and any knowledge or assistance.

I had a similar experience with a 2020 iMac 27". This was a high-end iMac (core I9, 64GB RAM, 2 TB SDD, 2.5 GB ethernet). In addition to slow network speed, the iMac also had kernel panics with system logs pointing to a hardware component. Extensive troubleshooting steps with re-installing macOS, resetting SMC, changing network switches, ethernet cables, external docks and dongles, etc., failed to resolve the problem. I took the iMac to the Apple Store Genius Bar where a logic board problem was confirmed. A “firmware” upgrade resulted in no improvement. The logic board was replaced TWICE, finally resolving the problem only after the second logic board replacement.

Since you have done extensive troubleshooting already, I recommend taking your MBP to the Genius Bar. I understand that they will do a diagnostic check at no charge. Even if it is not economically feasible to repair that MBP (considering the new M1 Macs), you will at least have the answer.

I eventually resolved all of this by using a 2020 13" M1 MBP for several months and eventually buying a Mac Studio. I convinced Apple to replace my repaired iMac with a new iMac because there was a mistake with the 2nd logic board replacement - the wrong logic board was installed. I sold that “new” replacement and used the proceeds toward the Mac Studio.

Like I had to do, you might just have to throw money at the problem.

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I think Arthur has it, but I’m curious what speeds you are seeing (i.e. how bad the problem is.) I tried to read your post closely for the number; sorry if I’ve missed it.

Good to know I’m not alone in seeing this issue. My work actually “upgraded” me to this MBP from a 2017 15” MBP after I requested a new device soon after the M1 Pro/Max MBPs were announced, so I’ll probably just hold on to this device for a bit to avoid being a nuisance to our IT department.

Thankfully my wifi speeds are by no means slow (200-300mbps) and all my work can be accomplished on a personal device, so I’ll probably wait a few more months to see if a prospective M2 Mac Mini will meet my ideal purchase criteria and if not I’ll pull the trigger on a Mac Studio and be rid of these problems for the foreseeable future.

On my MBP at issue, I’m seeing speeds ranging from ~50-300mbps upload and download. On my other devices I’m seeing ~900mbps upload and download.

Wifi speeds in my home office are ~200-300mbps so this is by no means a dire problem, but I would certainly prefer to get the totality of my internet connection if possible.

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Given the thoroughness of the troubleshooting measures described above, you probably already did the following, but just for completeness I’ll mention other possible steps:

SMC reset.
NVRAM reset.
Reset network settings.
Check your router settings, ensure that QOS or specific-device (MAC address) settings don’t throttle your device.
Re-install macOS.
Connect directly to your cable modem for another test, bypassing all existing switches and ethernet cables.

One more thing - probably doesn’t apply to you since your other devices exhibit normal internet connection speeds:
If applicable for your router, direct the router to perform an internet connection speed test (see below):

The designated router for my Eero Pro 3-unit mesh system is partially controlled by Eero’s cloud servers and regularly (usually daily) performs a speed test. Recently I upgraded my cable internet service tier to “gigabit” download speed. My actual connection speed (approx. 180 Mbps) did not change, despite intervention of the cable company’s support, multiple modem, router and computer re-boots, etc. After a period of head-scratching, gnashing of teeth and deep thinking … the thought of directing my Eero router to perform its own speed test finally occurred to me. Voilà! After the router’s speed test, my download speed to the computer was 930+ Mbps. Apparently the “smart” router regulated local network traffic to “optimize” performance with my internet connection speed.

I tried an SMC reset and that didn’t help.

Noticed while speed testing after that reset that my CPU temps spike from ~72ºC (idle) to upwards of 88ºC during a speed test, so I’m pretty convinced the issue here is solely thermal throttling.

Thanks for your assistance.