S21 Ultra stuck searching for signal, can't connect to mobile data

[Kelsey Thurman]

(searching) and signal bar is crossed out

Ever since my phone restarted it has been stuck searching for signal when on mobile data. I am able to connect to WiFi and use bluetooth but I get nothing related to mobile data. I have tried all the common fixes for this with no luck. I have pretty much narrowed it down to a hardware problem. My question is: what components could possibly cause this. I am aware that there are a few different antennas inside the S21 Ultra but I have not been able to find much detail regarding the function of each. Could a bad 5G antenna be the cause of this or would the symptoms be different if it was? Again, I don't have any mobile data, even when turning off 5G in the settings. If anybody has experience working on the S21 Ultra or know what may be causing this issue your help would be greatly appreciated. Thanks!

[Da6xn9]

Have you tried changing the access point? If you go to Connections > Mobile networks > Access point names, make sure the correct APN is connected. You can check the correct APN on your SIM provider's website.

[Kelsey Thurman]

Yep, I've tried but sadly no luck. 

[Da6xn9]

1) Do phone calls work?
2) Have you tried putting your SIM in a different phone?
3) Which network provider are you with?

[Kelsey Thurman]

I'm with tmobile. Phone calls work on WiFi and the SIM works in other phones.

[Da6xn9]

Do phone calls not work without WiFi?

[Kelsey Thurman]

Nope. They only work with WiFi on because tmobile allows calls and texts over WiFi. With WiFi off it gets no signal at all.

[mfbas]

Hi Kelsey, I am experiencing the exact same things you have described. I have a galaxy s21, and my provider is metro pcs, which I believe mainly runs on t-mobile's network.

I've been having this problem for about 2 weeks now, and I went to the extent to reach out to my provider and had them restart my line on their end. That helped for a bit, but after a few days I'm back to where i started. 

Before reading your post, like you I had come down to the conclusion that my problem must be a hardware issue. But now, I'm not so sure, the only thing that I could think has changed was the latest update on my phone, which was a few days before I started having any of these network problems. Did you happen to notice this after the update too by any chance??

[umbnich]

Same problem here, have you solved?

[Dave_G]

I have had similar issues since the last update on December 22nd to Android 14 & One UI 6.0.  I lost all mobile data ability.  However, my carrier was an MVNO on the Verizon network and they said that the issue is with Samsung and a defect in the S21 Ultra.  I don't hold out hope that this will be resolved since my S21 Ultra is now at end of life updates except for security patches (to my understanding).  My carrier's fix was to port me to T-Mobile network with manual configuration using APN Alter app (and a lot of help).  Both of my S21 Ultra's worked well until the last major update.