How To Guide G998U and G998U1 Firmware Links and Flashing Discussion Here

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mapl.ph

Senior Member
Feb 18, 2012
152
6
PH
Samsung Galaxy S21 Ultra
No, that's not an AT&T version. All bands should be enabled in all firmwares, but whatever your Service Provider SW is set to is probably what determines priority

I live in the Philippines, I feel that flashing my unit to U1 locked me to US bands. I'm currently not receiving 5G signals on the phone. What I have is the 12/128 Snapdragon variant and my network here supports n78 (3500) 5G bands. Few questions below for clarification.

1. Will sm-g998u1 firmware lock me to US bands? As mentioned I'm not receiving 5G signals here in the Philippines.

2. Will flashing sm-g998w fix my issue with 5g signal?

Any help is appreciated. Thanks
 

iBowToAndroid

Senior Member
Nov 9, 2010
5,183
1
1,644
Twin Cities MN
I live in the Philippines, I feel that flashing my unit to U1 locked me to US bands. I'm currently not receiving 5G signals on the phone. What I have is the 12/128 Snapdragon variant and my network here supports n78 (3500) 5G bands. Few questions below for clarification.

1. Will sm-g998u1 firmware lock me to US bands? As mentioned I'm not receiving 5G signals here in the Philippines.

2. Will flashing sm-g998w fix my issue with 5g signal?

Any help is appreciated. Thanks
You need to research and see which bands are supported by U1 and W models. It's possible that they don't support your bands at all, since you're on the other side of the world. If you want guaranteed band support, you always buy a model from your own country, not a different country
 

Ptuk

Member
Mar 22, 2022
20
1
You need to research and see which bands are supported by U1 and W models. It's possible that they don't support your bands at all, since you're on the other side of the world. If you want guaranteed band support, you always buy a model from your own country, not a different country
That's precisely what he is doing by posting. As of last year n78 wasn't on u1 and w but it might yet be as I think this band is coming in to use in the US. Whether it gets facilitate by a carrier or by Samsung i don't know. There used to be a way of doing it via dialler codes.
 

death365

Senior Member
Finally available for G998U1 xxa

Screenshot_20220328-032822_Software update.jpg
 
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blake .l

Senior Member
May 6, 2011
364
25
53
Newport
I flashed the U1 firmware to my Sim locked and boot loader locked AT&T S21 Ultra 5G. Does it affect the 5G? as of now I don't have a 5G plan so it show LTE+ When I do get my 5G plan the phone should still work correctly and pick up the 5G signal correct? I thought under service provider it was supposed to change from ATT to XXA? mine says ATT/ATT,ATT/ATT
 

kmdigital

Member
Mar 4, 2022
43
2
Samsung Galaxy S21 Ultra
I flashed the U1 firmware to my Sim locked and boot loader locked AT&T S21 Ultra 5G. Does it affect the 5G? as of now I don't have a 5G plan so it show LTE+ When I do get my 5G plan the phone should still work correctly and pick up the 5G signal correct? I thought under service provider it was supposed to change from ATT to XXA? mine says ATT/ATT,ATT/ATT
Yes, since it was an ATT device originally it'll work great. However, if you switch carriers there's a good chance that it won't work properly. I have an unlocked TMo S21U that I flashed to U1, and it doesn't work properly with VZW 5G, though 4G LTE works great. This seems to be because the CSC is stuck on ATT/ATT/TMB/TMB. What's interesting is that prior to flashing to U1, it was ATT/XAE/TMB/TMB (because I originally used it with an ATT MVNO. However, now that I've switched to a VZW MVNO, it stays stuck on only ATT & TMB, and it will NOT switch to VZW. I think I've found the answer at the link below, but I haven't tried implementing this yet. Short version, is that flashing to U1 seems to break the carrier switching, and extra steps need to be taken to get what's needed. https://www.reddit.com/r/GalaxyS21/comments/roqwkc
 
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blake .l

Senior Member
May 6, 2011
364
25
53
Newport
Ok this is the first time I noticed this but I went from the G998U to the G998U1 version of the firmware and my check for update button is gone. Is this normal? I dont guess its a big deal as long as I can get new firmware downloads over the net or here when they are available
 

Limon_Lime

Senior Member
Apr 19, 2017
136
3
Hello, I'm having an issue getting Visible service working on my Galaxy S21 Ultra SM-G998U1.

I purchased the phone on Swappa so I'm not sure exactly what carrier or model its from. But it should be factory unlocked and I can't call, text, or get data.

I tried installing a Verizon sim but still nothing. T-Mobile sim works perfectly though. And I've tried all the troubleshooting steps like network reset, adding APNs, even factory reset.

When I boot the phone or cycle airplane mode, occasionally 5G will turn on for a few seconds and immediately disconnect again.

The APNs all install automatically when I put the SIM in but i just don't get any service, even though it's showing full bars.
 

kmdigital

Member
Mar 4, 2022
43
2
Samsung Galaxy S21 Ultra
Are you 100% sure that it's a factory U1 phone? It sounds like it was a U phone, specifically for T-mobile, and if it says U1, someone flashed it to U1 even though it originally was a U phone. Go to About Phone/Software Information, and then about the 9th line down to Service Provider Software Version and let us know what it says. It will very likely have TMB as the last of 4 listed codes, and more than likely, it'll be TMB on at least 3 out of the 4 codes.
 

Limon_Lime

Senior Member
Apr 19, 2017
136
3
Are you 100% sure that it's a factory U1 phone? It sounds like it was a U phone, specifically for T-mobile, and if it says U1, someone flashed it to U1 even though it originally was a U phone. Go to About Phone/Software Information, and then about the 9th line down to Service Provider Software Version and let us know what it says. It will very likely have TMB as the last of 4 listed codes, and more than likely, it'll be TMB on at least 3 out of the 4 codes.
It says ATT/ATT/ATT/VZW

Does that mean it was originally an ATT or Verizon phone?
 

kmdigital

Member
Mar 4, 2022
43
2
Samsung Galaxy S21 Ultra
No, it was originally a Verizon phone, interestingly enough. However, it was then used on ATT, and for whatever reason, it's not properly picking up the VZW CSC and switching back to it again. If it were at factory U1 phone, the CSC would be XAA on at least 2 of them, and it would automatically switch to VZW when the SIM is installed. In another thread, after a lot of research, it seems that the S21 phones, even when flashed to U1, aren't true U1 phones and will always keep the original vendor as the last code in the CSC list. I had a similar issue with Visible on an original TMB phone, and this is how I resolved it,

It's not difficult (though it does take about 15 - 30 minutes depending on how long it takes to download everything that you need), particularly on a brand new phone where you don't have things set up yet. If you have the phone configured and don't want to redo everything, then you'll need to use the Home CSC file as described, not the other one. If nothing is configured, then I'd probably use the other one. Basically, you need to reflash to U VZW and call that good if you don't mind the Verizon bloatware, or flash it again to either U1 VZW or U1 XAA to get rid of the bloatware. I'm not sure if U1 VZW has bloatware or not, but it may. I do know that XAA doesn't, and I really like the Smart caller ID function that I got after flashing to U1. Essentially, that seems to use any publicly available Google phone number info and automatically provide the caller ID name for any dialed or received calls. This may or may not be on the VZW firmware, as I didn't try it.
 

Limon_Lime

Senior Member
Apr 19, 2017
136
3
No, it was originally a Verizon phone, interestingly enough. However, it was then used on ATT, and for whatever reason, it's not properly picking up the VZW CSC and switching back to it again. If it were at factory U1 phone, the CSC would be XAA on at least 2 of them, and it would automatically switch to VZW when the SIM is installed. In another thread, after a lot of research, it seems that the S21 phones, even when flashed to U1, aren't true U1 phones and will always keep the original vendor as the last code in the CSC list. I had a similar issue with Visible on an original TMB phone, and this is how I resolved it,

It's not difficult (though it does take about 15 - 30 minutes depending on how long it takes to download everything that you need), particularly on a brand new phone where you don't have things set up yet. If you have the phone configured and don't want to redo everything, then you'll need to use the Home CSC file as described, not the other one. If nothing is configured, then I'd probably use the other one. Basically, you need to reflash to U VZW and call that good if you don't mind the Verizon bloatware, or flash it again to either U1 VZW or U1 XAA to get rid of the bloatware. I'm not sure if U1 VZW has bloatware or not, but it may. I do know that XAA doesn't, and I really like the Smart caller ID function that I got after flashing to U1. Essentially, that seems to use any publicly available Google phone number info and automatically provide the caller ID name for any dialed or received calls. This may or may not be on the VZW firmware, as I didn't try it.
Ok so I tried downloading the latest VZW firmware from samfw.com.. but it gave me an AT&T logo on boot.
 

kmdigital

Member
Mar 4, 2022
43
2
Samsung Galaxy S21 Ultra
You need to install the Verizon SIM to make it switch, so you should have flashed it without any SIM in it, or with the Verizon SIM. Have you tried that? When you insert the Verizon SIM it should tell you to reboot it, at which time it'll now come up with the Verizon logo. You can leave it at that or reflash again to XAA U1 to get rid of the logo on boot.
 

Limon_Lime

Senior Member
Apr 19, 2017
136
3
You need to install the Verizon SIM to make it switch, so you should have flashed it without any SIM in it, or with the Verizon SIM. Have you tried that? When you insert the Verizon SIM it should tell you to reboot it, at which time it'll now come up with the Verizon logo. You can leave it at that or reflash again to XAA U1 to get rid of the logo on boot.
It doesn't ask me to reboot, just pulls up the SIM card info and allows me to press "Done".

I flashed it with the Visible sim inside but it still had an ATT logo on boot.
 
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kmdigital

Member
Mar 4, 2022
43
2
Samsung Galaxy S21 Ultra
Hmm, it won't work unless it reboots to Verizon when the SIM is installed. I'd remove the Visible sim, reflash again making sure that you're using the U VZW firmware, reboot and then insert the SIM. It worked for me....
 

Limon_Lime

Senior Member
Apr 19, 2017
136
3
Hmm, it won't work unless it reboots to Verizon when the SIM is installed. I'd remove the Visible sim, reflash again making sure that you're using the U VZW firmware, reboot and then insert the SIM. It worked for me....
I flashed Samfw.com_SM-G998U_VZW_G998USQS5CVCB_fac.zip. Is that supposed to be the right one?
 

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    For those who aren't already aware, G998U is the model number of all of the US carrier versions of the S21 Ultra. The G998U1 is the model number of the same device, but sold by Samsung SIM unlocked and with no carrier bloatware. Firmware is 100% interchangeable among these models: any U or U1 firmware version can be flashed to any U or U1 device at any time, assuming that you're not trying to downgrade the bootloader. A "U to U" or "U1 to U1" flash does not require a factory reset, but changing from one firmware to the other will require one. Also, U firmware is identical for the 4 base files (AP, BL, CP, CSC) for each individual build, no matter which carrier it comes from. So if you download 2 different carrier versions of the exact same build, the 4 base files will be identical. Where the firmware differs is in the USERDATA file - that's where the carrier bloatware and customizations reside.

    Manual Odin flashing is designed for those who:

    - want to manually update to a newer version of U firmware on their U device, either because they don't want to wait for their carrier's OTA or because OTAs aren't working on their device, or a different carrier got a new feature/patch before they did
    - want to flash U1 firmware to their U device
    - want to convert from U1 firmware to carrier U firmware
    - want to convert from one carrier's U firmware (with all apps and bloatware) to a different carrier's U firmware (with all apps and bloatware)

    For those who aren't already aware, anyone can now download firmware for almost any Samsung device any time that they want, via the various firmware download tools posted here on XDA like SamFirm or Frija. There are threads and info about them here on XDA so I won't waste time explaining - do a search if you're not already familiar with these tools. But they only provide whatever the latest/newest/current version is - nothing older. I pay for a subscription to a site that gets the official releases (usually) before they hit the firmware download tools, so that's where my files come from.

    This is not a "beginner's guide to Odin flashing" -type post/thread, so I won't list basic, step-by-step flashing instructions. My threads are geared towards those who already know what they're doing. If you're new to manually flashing Samsung firmware (or haven't done it in a long time), I recommend you consult one of those "beginner's" guides- there are tons of them here on XDA.

    Happy flashing!

    U firmware: https://www.androidfilehost.com/?w=files&flid=322089
    U1 firmware: https://www.androidfilehost.com/?w=files&flid=322090

    Notes:

    - DON'T QUOTE THE OP WHEN YOU REPLY, kthx

    - I have lots of threads just like this one for other Samsung flagships, if it interests you. For those who have already made use of my previous threads for a different device and are upgrading to an S21, welcome back :)

    - My zips are compressed extra small for space and bandwidth savings. The default Windows extractor can't handle it, so you'll need a 3rd party tool like 7zip, WinRAR, etc

    - it's quite time consuming to download the files, zip them up, and upload them to AFH. And, I do threads like this for every single Sx and Note x model, so I won't be uploading every single version. The only full builds that I upload are ones where I get access to a new bootloader and/or Android version early, before they hit the firmware download tools.

    - My naming method for folders on AFH is: build - bootloader - Android version
    So "SAT - 1 - 9.0" means the full build number ends in SAT, it's bootloader version 1, and it's Android 9.0. When bootloader and Android versions increment, the first build to have those changes will have its folder notated appropriately.

    - HOME CSC file keeps data intact; using the other CSC will wipe data. Flashing USERDATA will also wipe data.

    - Since AT&T doesn't allow their firmware to be publicly available (for any of their devices), I'll try to always upload at least one USERDATA per bootloader increment for AT&T (and Cricket, if they get this model). I'll also upload any full builds if AT&T is the only carrier to get that specific build, because you won't be able to find the files anywhere else.

    - For identifying USERDATAS, and to know what region/CSC to use in the firmware download tools if you're downloading yourself:

    AIO = Cricket (not available via firmware download tools)
    ATT = AT&T (not available via firmware download tools)
    BST = Boost Mobile
    CCT = Xfinity Mobile (Comcast)
    CHA = Spectrum Mobile (Charter)
    DSH = Dish Network
    SPR = Sprint
    TMB = T-Mobile
    TMK = Metro PCS
    USC = US Cellular
    VZW = Verizon (available via firmware download tools, but Manual Entry is required - Auto will not work)
    XAA = U1 firmware

    - the correct procedure for switching from one carrier's firmware to another carrier's firmware is:
    1. Flash full U1 firmware package including non HOME CSC
    2. Upon boot, insert a SIM of the carrier whose firmware you want
    3. Watch for the popup that says "reboot to apply new carrier settings" etc, and do it
    4. After that restart completes, reboot back to Download mode and flash the full U firmware package, with the USERDATA file of the carrier whose firmware you want
    2
    Initial U firmware and AT&T USERDATA are posted, along with U1 firmware. U firmware is not yet accessible in the firmware download tools like SamFirm and Frija, but if anyone wants a different carrier's USERDATA (for flashing bloatware to a U1 device or for converting a U device from one carrier's bloatware to a different one), let me know and I'll get it for you
    2
    Could you please find me the USERDATA for Verizon please?
    U firmware is now live on Samsung's servers, so anyone can use the various firmware download tools like SamFirm or Frija to get whatever they need (AT&T and Cricket excluded)
    If I have tmo and flash u1 will I still receive ota updates in the future? Or will I manuallt have to flash new update everytime?
    Yes, you'll get OTAs
    2
    Okay, post deleted, but it's probably worth noting that you don't know what the G998W is. Because it's the same phone as the U and U1. During the One UI 3.0 Beta on the S20 Ultra, I flashed G988U on my G988W, and when the beta continued onto the U1, I flashed those firmware files as well. The Canadian S20/S21 is just a non branded T-Mobile with more supported radio bands in the firmware.

    If you actually look at the carrier info for the S20 Unlocked U/U1/W firmware, they all say XAC and XAA at the bottom no matter whether it's U/U1/W. They are all the same phone and Samsung even uses the same firmware merged, just different radio bands, and because Canadian radio bands support ALL bands, it makes the W firmware the a merge of both U and U1, so it's actually the better choice from what you have posted because it supports every U/U1/W the best. So your post is relevant to the W models whether you want to accept it or not.

    That's why I included a link to the firmware, because it's the same device, same flashing process, completely same procedure, so this thread IS relevant to the W models even if you said U and U1 only, the W is also included in that even if you didn't say it was, doesn't make it true.

    Also the only difference between U and U1 is U is unlocked but INCLUDES carrier bloat, U1 is unlocked and has NO carrier bloat.

    So, closing info here.

    U1 is unlocked, no carrier bloat, US radio bands
    U is unlocked, HAS carrier bloat, US radio bands
    W is unlocked, no carrier bloat, ALL radio bands

    You just need to make sure it's the SM-G998W for AXC and it's the best choice with no bloat.
    Just because you clearly didn't know this about the W phones, doesn't mean you gotta get all snappy, I'm just trying to help the community.
    2
    I would think you would have most features since the U1 firmware is sold by Samsung to work on networks like T-Mobile. However, all I can verify for you is that I got my wifi calling and I have a 5G icon with 305Mb on speed test. This is after flashing U1.

    I had the same issue. Out of the box, without even turning the phone on, I flashed the U1 firmware on my T-mobile S21 ultra but the device just kept saying "NO SIM"

    If you have a T-mobile device, turn it on with an active sim card first with the original U firmware. Don't need to go through the setup, just have to let it find a LTE/5G signal. After that you can power down and flash U1 firmware and won't have any SIM issues.

    Hope this might help anyone who might run into the same issues we did