Last Updated: June 3, 2026
Getting your SM-G991B/DS Galaxy S21 5G back to normal is easy when you use the official Samsung Galaxy S21 5G SM-G991B/DS firmware. You will find every file and step you need right here, including tools, drivers, and guides for FRP bypass, hard resets, and IMEI repair.
Device: Samsung Galaxy S21 5G SM-G991B/DS | Chipset: Samsung Exynos 2100 (5 nm) | Flash Tool: Odin
Android: Android 11, One UI 3.1 | File Type: .tar.md5 / ZIP (Contains AP, BL, CP, CSC files for Odin)
⚠ Warning: Flashing erases all data. Back up first.
Samsung Galaxy S21 5G SM-G991B/DS Firmware (Flash File) Drivers, Tools & Guide
Installing the official Samsung Galaxy S21 5G SM-G991B/DS firmware requires the correct Odin version, the right drivers, and the exact flash files for your specific model. Using Odin to install stock software on your phone is a simple process if you have the correct files. I have gathered everything you need right here to get the job done without any guesswork.
Before you do anything else, sign out of your Samsung account if one is currently logged in. Skipping this step will trigger Knox security, and fixing a KG lock later takes much more effort. When you download the software, it arrives as a ZIP file. Use WinRAR or 7-Zip to extract it. You should see files labeled AP_*.tar.md5, BL_*.tar.md5, CP_*.tar.md5, and CSC_*.tar.md5 (or HOME_CSC_*.tar.md5). If those files are missing, you downloaded the wrong package.
Remember that installing stock software completely wipes your phone. This is exactly what you want if you are trying to fix software bugs, remove FRP locks, fix battery drain, or recover a device stuck on the logo.
Hard Reset Samsung Galaxy S21 5G SM-G991B/DS
You can factory reset the Samsung Galaxy S21 5G SM-G991B/DS without a computer by holding the Volume Up and Power buttons together until the recovery menu loads. Once the menu appears, use the volume keys to highlight “Wipe Data/Factory Reset” and press the Power button to confirm your choice.
Performing a hard reset wipes everything and returns the phone to its factory settings. This usually clears up common glitches like forgotten screen locks, freezing, and constant restarting. If the phone still acts up after the reset, flashing the full software with Odin is your next step.
Samsung Galaxy S21 5G SM-G991B/DS FRP Bypass
The easiest way to bypass FRP on the Samsung Galaxy S21 5G SM-G991B/DS is by using a free Android apps launcher to access settings during the initial setup screen. I have been there, and a Google account lock is frustrating to deal with after a reset. You can use our free Android apps launcher to get past it quickly. To avoid this completely, always remove your Google account before wiping the device.
Why Do We Need Samsung Galaxy S21 5G SM-G991B/DS Firmware?
Flashing the official Samsung Galaxy S21 5G SM-G991B/DS firmware is necessary to fix severe software issues, update the operating system, or recover a bricked phone. Samsung phones are flashed using Odin, no matter which processor they use. Installing the official software will resolve most of the problems you might encounter:
- Remove locks if the phone is disabled.
- Install the newest Android version available for your specific model.
- Stop freezing, lagging, and continuous bootloops on your SM-G991B/DS Galaxy S21 5G.
- Fix battery drain and over-the-air update errors.
- Bring the phone back to its original factory state to keep your warranty valid.
- Recover the device if it only boots into the recovery menu.
- Fix KG lock or Knox errors caused by a bad flash.
Learn more about stock ROMs and why flashing works.
Choosing the Right Firmware Version
You must verify your exact model number, region code, and binary level before downloading the right firmware version for your phone. Do not worry if this seems confusing at first. Installing the wrong file is a tough mistake to fix, so take a minute to check these details:
- Check Your Exact Model: Open Settings › About Phone and read the full model number (like SM-G991B/DS). The letter at the end is important, U/U1 means USA, W is Canada, N is Korea, and B/F is International/Global. Using the wrong variant causes major errors.
- Match the CSC Region: The 3-letter code in the file name needs to match your phone. You can find your current CSC under Settings › About Phone › Software Information, or check Download Mode. Common codes include XAA (US), BTU (UK), INS (India), and SER (Russia).
- Look at the Binary Level: Check your current software version string (for example,
XXU9BZDP). The number after the letters is the binary level. You cannot downgrade this number. If you are on Binary 9, you must use Binary 9 or higher. - Check the Build Date: The last 4 characters of the PDA show the build date. The first letter is the year (A=2024, B=2025, C=2026), and the second is the month (A=Jan through L=Dec).
- Verify in Download Mode: Turn off the phone and hold Volume Down + Power to open Download Mode. This screen lists your exact model, CSC, and software version so you can double-check everything.
Firmware Details for Samsung Galaxy S21 5G SM-G991B/DS
The official firmware specifications for the Samsung Galaxy S21 5G SM-G991B/DS include Android 11, One UI 3.1, and a file size of 716.82 MB.
| Firmware Information | Details |
|---|---|
| Device Model | Samsung Galaxy S21 5G SM-G991B/DS |
| Firmware Version | V00 |
| File Size | 716.82 MB |
| Android Version | Android 11, One UI 3.1 |
| Platform | Samsung Exynos 2100 (5 nm) |
| Release Date | Released 2021, January 29 |
| Region | Global, Africa and Asia |
| File Type | .tar.md5 / ZIP (Contains AP, BL, CP, CSC files for Odin) |
Which Firmware Version Should I Download?
You should download the firmware version that matches your specific situation, such as choosing the latest version for a dead phone or an older version if the latest OTA caused bugs. I get asked this all the time, so I created this quick reference table. Find your scenario and grab the correct file:
| Your Situation | What I Recommend |
|---|---|
| Phone is completely dead or stuck on logo | the latest version, download this one. It is the latest Samsung Galaxy S21 5G SM-G991B/DS firmware available. |
| FRP / Google account lock only | See the FRP bypass guide above, you likely do not need the full firmware for this. |
| Not sure which region/CSC to download | Check Settings › About Phone › Software Information for your current CSC, or enter Download Mode (Volume Down + Power), it shows the CSC on screen. Match the 3-letter code (e.g. XAA, BTU, INS) to the firmware filename. |
| Phone slow after a recent OTA update | Try the next older version, sometimes the latest OTA introduces new bugs and an older build runs better. Make sure the binary level is the same or higher than what your device currently has. |
| IMEI missing after a previous flash | Re-flash the latest version first, then follow the IMEI repair guide. Do not skip the reflash. |
| the latest version failed with a flash error | Try the next older version instead and double-check your AP/BL/CP/CSC file assignments in Odin before assuming the firmware is the problem. |
| Restoring to factory / warranty repair | the latest version, clean state, fresh start. |
To tell which Samsung firmware is newer, look at the last 4 characters of the PDA version string (e.g. S938BXXU9CZDP). The first character is the year (A=2024, B=2025, C=2026), the second is the month (A=Jan, B=Feb… L=Dec, Z=final stable), and the last two are the revision (0-9 then A-Z, where Z is highest). But before comparing dates, always check the binary level: the digit just before the date code (e.g. XXU9CZDP = Binary 9). You cannot downgrade to a lower binary level. If your device is on Binary 9, only flash Binary 9 or higher. Also make sure the 3-letter CSC code in the firmware matches your device region.
Download Samsung Galaxy S21 5G SM-G991B/DS Firmware
You can download the official Samsung Galaxy S21 5G SM-G991B/DS firmware directly from the links provided below. The most recent release is the latest version. Once the download finishes, check that the file size matches the details listed earlier. If the size is different, the file might be corrupted, and installing it will only create more problems.
| Software Details | Download Link | Members Link |
|---|---|---|
|
File Name: COMBINATION_FAC_FA81_J610GUBU1ARI4_FACFAC_CL14321305_QB19776235_REV00_user.rar Size: 716.82 MB | Download Link | Download Link2 |
Only download firmware that is fully compatible with your exact device model. See the firmware selection guide above if you are not sure.
- Your model number is a variant of SM-G991B/DS with a different letter suffix. Check About Phone carefully, one letter difference can cause a failed or broken flash.
- Your chipset differs from Samsung Exynos 2100 (5 nm). Confirm in recovery mode before proceeding.
- You downloaded the file from a source other than this page.
- The file size differs significantly from the sizes listed in the table above, a size mismatch usually means a partial download, which will fail mid-flash.
Prerequisites for Samsung Galaxy S21 5G SM-G991B/DS Firmware
The main prerequisites for flashing the Samsung Galaxy S21 5G SM-G991B/DS firmware include backing up your data, removing all accounts, and installing the correct USB drivers. Check these items off your list before opening Odin. Two things cause the most headaches: leaving a Samsung account logged in (which causes KG lock) and using a cheap charging cable that disconnects during the flash. Always use a high-quality data cable.
- Back Up IMEI Numbers: Dial *#06# and write down both IMEI numbers right now. You will need these if you have to restore your IMEI after flashing.
- Remove Google Accounts: Sign out of all Google accounts to prevent FRP lock after flashing.
- Remove Samsung Accounts: Sign out of all Samsung accounts to avoid KG lock.
- Back Up Your Data: Save your photos, contacts, WhatsApp chats, and important files. Flashing wipes the device completely.
- Charge Your Device: Ensure you have at least 50% battery. A device that powers off during a flash is very difficult to recover.
- USB Cable & PC: Use a proper data USB cable and a Windows computer with available USB ports.
- Install Required Drivers:
How to Install Firmware on Samsung Galaxy S21 5G SM-G991B/DS
You can install the firmware on your Samsung Galaxy S21 5G SM-G991B/DS by using the Odin flash tool to load the AP, BL, CP, and CSC files while the phone is in Download Mode. We will use Odin for this process. Make sure “Auto Reboot” and “F. Reset Time” are both checked in Odin for the best results. If you need help picking an Odin version, visit our Odin versions page.
- Download and Extract:
- Download the correct firmware package from the links above.
- Extract the ZIP to a simple folder path. Avoid paths with spaces or special characters, as some flash tools have trouble reading them.
- Install the Listed Drivers:
- Confirm all drivers listed above are installed and that your PC has been restarted. Skipping the restart is a common reason drivers do not work correctly.
- Load the Firmware File:
- In Odin, click “BL” and select the BL_*.tar.md5 file. Click “AP” and select the AP_*.tar.md5 file. Repeat for “CP” and “CSC”. Use HOME_CSC to keep data, or CSC for a clean flash.
- Connect Your Device:
- Enter Download Mode: Turn off your phone, then hold Volume Down + Power until the warning screen appears. Press Volume Up to confirm and enter Download Mode.
- Connect your phone to your PC via USB. Odin should show “Added..” in the log area, which means your device is detected.
- Start Flashing:
- Click the “Start” button to begin.
- Do not disconnect, move the cable, or touch the device until the process is fully complete. Disconnecting mid-flash is how devices get bricked.
- Wait and Reboot:
- Once flashing finishes successfully, disconnect the device.
- Power on your device. The first boot will take longer than usual, so give it up to 8 minutes.
Video Guide for Flashing
What to Expect After Flashing Samsung Galaxy S21 5G SM-G991B/DS Firmware
After flashing the Samsung Galaxy S21 5G SM-G991B/DS firmware, you should expect a longer first boot time, warm device temperatures, and a complete wipe of your personal data. Many people panic and think they broke their phone when everything is actually working perfectly. Here is what is completely normal:
- How to know the flash was successful: Odin will display “PASS.” in green text at the top-left of the log area. Seeing this means everything went exactly as planned.
- First boot takes 3 to 8 minutes, do not force-reboot the device. The operating system is setting itself up from scratch. Interrupting this process causes bootloops.
- The phone will feel warm during first boot, this is expected behavior. The device will cool down after a few minutes once the initial setup finishes.
- All your apps are gone, this happens by design. Reinstall them from the Play Store. If you had a Google account backup active, it will offer to restore your apps automatically during setup.
- Dial *#06# immediately after setup to check your IMEI. Do this before you insert a SIM card. If it shows “unknown” or “null”, follow the IMEI repair guide below before doing anything else.
- Be careful when re-adding your Google account, if you did not remove it before flashing, you may see an FRP prompt. Add it fresh during the setup wizard, not afterwards through Settings.
- Wi-Fi, Bluetooth, and mobile data should all work right after setup. If mobile data is not connecting, go to Settings › SIM and Network and re-enter your APN manually, the flash sometimes clears carrier APN settings.
- Stuck in a bootloop after first boot? Enter recovery mode and do a factory reset from there, see the hard reset guide above. This can happen occasionally and does not mean the firmware is wrong, it is usually a conflict with leftover data from the old install.
- Samsung Smart Switch: After flashing your Samsung Galaxy S21 5G SM-G991B/DS firmware, Samsung Smart Switch may prompt you to install additional updates. Let it complete, this ensures your device has the latest security patches for your region.
Missing IMEI or Corrupt Baseband on Samsung Galaxy S21 5G SM-G991B/DS After Flashing?
A missing IMEI after flashing usually means the EFS partition became corrupt, which you can often repair using dedicated software tools. Do not worry if this happens. The EFS partition holds your IMEI and network data. Restoring an IMEI that does not belong to your phone is illegal in many places, so only restore your original numbers. Programs like ChimeraTool or BFT can fix this issue. Please check your local laws first.
Video Guide: How to repair IMEI
Common Issues When Flashing Samsung Galaxy S21 5G SM-G991B/DS
- Odin Shows “FAIL” Instead of “PASS”:
- This usually means there is a mismatch between the software region and your device. Double-check your exact model number in Settings › About Phone before selecting the file. Even a single letter difference in the model code will cause this error.
- Samsung Galaxy S21 5G SM-G991B/DS Not Recognized by Odin:
- Reinstall the Samsung USB drivers and ensure your phone is in Download Mode. Try using a different USB cable, because Odin can be sensitive to cable quality.
- KG Lock / Knox Triggered After Flashing:
- This error occurs when a Samsung account remained signed in before the flash, or if unofficial software was applied. Always sign out of Samsung accounts beforehand. If KG lock is already active, you generally need a professional unlocking tool.
- Boot Loop After Flashing:
- Open recovery mode (Volume Up + Power) and perform a factory reset. This clears out any leftover data from the previous installation that might be causing the conflict.
Frequently Asked Questions
Q1: Will flashing the Samsung Galaxy S21 5G SM-G991B/DS firmware erase my data?
A: Yes. Installing this software with Odin returns your phone to its factory state, which includes the default settings for Android 11 and One UI 3.1. Every app, photo, contact, and account will be deleted. Make sure to back up anything you want to keep before you begin, because you cannot recover data after the flash is done.
Q2: Is this firmware compatible with other Samsung models?
A: No. This package is made specifically for the Samsung Galaxy S21 5G SM-G991B/DS using the Samsung Exynos 2100 (5 nm) processor. Even another variant of the SM-G991B/DS might use a completely different chipset. Installing the wrong file can leave your phone very difficult to fix. Always verify your exact model number in Settings › About Phone.
Q3: Can I downgrade from the latest version to an older firmware version?
A: While it is technically possible on some Exynos builds, I advise against it. Rolling back can introduce security flaws and app compatibility errors on Android 11, One UI 3.1. If the newest update is giving you trouble, leave a comment below. There is usually a much better solution than downgrading.
Q4: What should I do if I encounter an FRP lock after flashing?
A: You can use our free Android apps launcher. FRP activates on the Samsung Galaxy S21 5G SM-G991B/DS if a Google account was still active before the flash. This is exactly why I suggest removing your Google account prior to flashing, it prevents the lock entirely.
Q5: Are custom ROM options available for the Samsung Galaxy S21 5G SM-G991B/DS?
A: This page only covers official Samsung stock software. The availability of custom ROMs for the Samsung Galaxy S21 5G SM-G991B/DS depends on whether the Samsung Exynos 2100 (5 nm) chipset has open-source kernel support. You can check our Custom ROMs page or browse the XDA Developers forum for specific custom ROM threads.
Q6: My Samsung Galaxy S21 5G SM-G991B/DS is not detected by Odin. What should I do?
A: Check your drivers first. Reinstall the Samsung USB drivers, restart your computer, and try again. Move to a USB 2.0 port if you are currently using USB 3.0, because Samsung phones connect more reliably to USB 2.0. Temporarily disable your antivirus software. If it still fails, leave a comment below with the exact error message and I will help you troubleshoot.
Q7: How do I enter recovery mode on my Samsung Galaxy S21 5G SM-G991B/DS?
A: Turn the phone off entirely, then press and hold Volume Up + Power together until the recovery menu shows up. If you have an older Samsung phone with a physical Home button, press Volume Up + Home + Power instead. The recovery menu will display the build number for your Samsung Galaxy S21 5G SM-G991B/DS, which is helpful for verifying your current software version.
Q8: My IMEI shows “unknown” after flashing the Samsung Galaxy S21 5G SM-G991B/DS. Is my phone permanently damaged?
A: No. It looks scary, but it is usually fixable. Follow the IMEI repair guide located in the troubleshooting section above. For Samsung phones, you should check the EFS partition for corruption first. Make sure you do not insert a SIM card until the IMEI is fully restored.
Q9: How long does it take to flash Samsung Galaxy S21 5G SM-G991B/DS firmware?
A: The actual installation in Odin typically takes 3 to 10 minutes, depending on the file size and your USB connection speed. The first boot after the installation takes a bit longer, usually between 3 and 8 minutes. Do not unplug or restart the phone during either phase. If the progress bar in Odin seems stuck, wait a few extra minutes before assuming something broke.
Final Thoughts on Samsung Galaxy S21 5G SM-G991B/DS Firmware
Following this guide will allow you to successfully install the official Samsung Galaxy S21 5G SM-G991B/DS firmware and restore your phone to full working order. If you followed each step carefully, your device should now be running a completely clean build.
If you ran into an unexpected error or if a specific step did not work for your setup, leave a comment below. Please include as much detail as possible, such as the exact error message, the step you are currently on, and the fixes you have already attempted. I read every comment and will help you figure it out.
If this article helped you fix your phone, please consider sharing it. Sharing is the easiest way to help someone else who might be facing the exact same issue.
Browse all Samsung firmware downloads for more devices.
Disclaimer: Flashing stock firmware is performed at your own risk. Follow the instructions on this page carefully. I cannot be held responsible for any damage to your device, but I will always try to help if something goes wrong.
