Last Updated: June 3, 2026
If your SM-G991Q is acting up, downloading the official Samsung Galaxy S21 5G SM-G991Q firmware is the best way to get it back on track. You will find all the necessary files right here, including flash tools, USB drivers, FRP bypass steps, hard reset instructions, and IMEI repair guides.
Device: Samsung Galaxy S21 5G SM-G991Q | Chipset: Samsung Exynos 2100 | Flash Tool: Odin
Android: Android 15, One UI 7 | 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-G991Q Firmware (Flash File) Drivers, Tools & Guide
Installing the Samsung Galaxy S21 5G SM-G991Q firmware using Odin is a simple task when you have the correct files and instructions. I have gathered the right Odin version and the exact steps you need right here on this page. Do not worry if this is your first time; just take it step by step.
Before you do anything else, make sure to sign out of your Samsung account if one is currently active. Skipping this step will trigger Knox security, and dealing with a KG lock takes much more effort to fix. Also, remember that Samsung packages its software in .tar.md5 format. Once you extract the main folder, look for files labeled AP_*, BL_*, CP_*, and CSC_* (or HOME_CSC_*). If those are missing, you might have downloaded the wrong package.
Your Samsung Galaxy S21 5G SM-G991Q firmware download will arrive as a ZIP archive. You can extract it using WinRAR or 7-Zip. Inside, you should see the AP_*.tar.md5, BL_*.tar.md5, CP_*.tar.md5, and CSC_*.tar.md5 (or HOME_CSC_*.tar.md5) files. If you do not see these, you may have the wrong firmware package for your device.
Keep in mind that installing stock firmware will wipe all your data. This is exactly what fixes persistent software problems like FRP locks, app crashes, sluggish performance, forgotten passwords, a phone stuck on the logo, connectivity issues, battery drain, and soft brick situations.
Hard Reset Samsung Galaxy S21 5G SM-G991Q
You can factory reset the Samsung Galaxy S21 5G SM-G991Q without a computer by turning the device off, then pressing and holding Volume Up + Power together until the recovery menu pops up. (For older models with a Home button, press Volume Up + Home + Power). Use the volume buttons to highlight “Wipe Data/Factory Reset” and press the Power button to confirm.
Performing a hard reset will completely erase your data and return the Samsung Galaxy S21 5G SM-G991Q to its factory defaults. This resolves most common software hiccups like lagging, app crashes, forgotten screen locks, and bootloops. If the problem sticks around after the reset, the full Odin flash guide in the next sections will take care of it.
Samsung Galaxy S21 5G SM-G991Q FRP Bypass
The quickest method to bypass FRP on the Samsung Galaxy S21 5G SM-G991Q involves using a free Android apps launcher to reach your settings during the initial setup. After a factory reset or a firmware flash, you might run into a Google account lock (FRP). I have been there, and our free Android apps launcher is the easiest way around it. This is exactly why I always suggest removing your Google account before you flash anything, it saves you from this headache entirely.
Why Do We Need Samsung Galaxy S21 5G SM-G991Q Firmware?
Flashing the official Samsung Galaxy S21 5G SM-G991Q firmware is necessary to resolve severe software issues, update the operating system, or recover a bricked phone. Samsung phones like the Samsung Galaxy S21 5G SM-G991Q rely on Odin for flashing, no matter which processor they use. Whether you are facing a boot failure or general software glitches, installing the official software usually fixes it:
- Unlock a device that has been disabled or locked.
- Upgrade to the newest Android version available for your phone.
- Stop startup loops, lagging, and freezing on your SM-G991Q Galaxy S21 5G.
- Fix battery drain and failed OTA updates.
- Bring back the original stock ROM to keep your warranty intact.
- Recover a phone that only boots into recovery mode.
- Fix KG lock or Knox errors caused by an interrupted or incorrect flash.
You can learn more about stock ROMs and why flashing works.
Choosing the Right Firmware Version
Selecting the correct firmware version for your Samsung Galaxy S21 5G SM-G991Q is crucial because flashing the wrong file can cause serious system errors. Take a moment to verify your files before you start. Installing the wrong software is a tough mistake to undo:
- Identify Your Exact Model Number: Open Settings › About Phone and check your full model number (e.g. SM-G991Q). The letter at the end is important, U/U1 means USA, W means Canada, N means Korea, and B/F means International/Global. Using the wrong variant causes problems.
- Match the CSC (Region): The 3-letter region code in the firmware name must match your phone. You can find your current CSC under Settings › About Phone › Software Information, or check the Service Provider line in Download Mode. Common codes include XAA (US), BTU (UK), INS (India), and SER (Russia).
- Check the Binary Level: Look at your current firmware version string (e.g.
XXU9BZDP, the number after the letters is the binary level). You cannot downgrade past this number. If your phone is on Binary 9, you must flash Binary 9 or higher. - Confirm the Build Date: The final 4 characters of the PDA version show the build date, the first character 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 the phone off, then hold Volume Down + Power to open Download Mode. This screen lists your exact model, CSC, and current software version, use it to double-check before you flash.
Firmware Details for Samsung Galaxy S21 5G SM-G991Q
The firmware details for the Samsung Galaxy S21 5G SM-G991Q include the device model, Android version, platform, and file type. Here is a quick overview of the official specifications:
| Firmware Information | Details |
|---|---|
| Device Model | Samsung Galaxy S21 5G SM-G991Q |
| Firmware Version | N/A |
| File Size | N/A |
| Android Version | Android 15, One UI 7 |
| Platform | Samsung Exynos 2100 |
| 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 directly addresses your specific issue, whether it is a dead phone, FRP lock, or a buggy OTA update. This is the question I get asked most often in the comments, so I put together a simple guide. Find your situation in the table and go straight to the right 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-G991Q 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-G991Q Firmware
You can download the official stock firmware for the Samsung Galaxy S21 5G SM-G991Q directly from the links provided below. The latest available version is the latest version. Once the download finishes, check that the file size matches the table above. A mismatched file size usually means the download was interrupted or corrupted, and flashing a broken file will only create more problems.
Only download software 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-G991Q 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. 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-G991Q Firmware
Before opening Odin to install the Samsung Galaxy S21 5G SM-G991Q firmware, you must complete a few prerequisites to ensure a smooth and successful flash. Go through this checklist first. Two things commonly cause headaches with Samsung phones: forgetting to sign out of your Samsung account (which triggers KG lock) and using a cheap charging cable that drops the connection halfway through. Always grab a proper data USB cable for this.
- Back Up IMEI Numbers: Dial *#06# and write down both IMEI numbers now. You will need these if you need 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: Back up everything, photos, contacts, WhatsApp chats, important files. Flashing wipes the device completely.
- Charge Your Device: 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, not a charge-only cable, and a Windows computer with available USB ports.
- Install Required Drivers:
How to Install Firmware on Samsung Galaxy S21 5G SM-G991Q
You can install firmware on the Samsung Galaxy S21 5G SM-G991Q by using the Odin flash tool to load the AP, BL, CP, and CSC files onto the device. We are using Odin for this. A quick tip: keep “Auto Reboot” and “F. Reset Time” both checked in Odin, those two options together give you the cleanest flash result. If you are not sure which Odin version to use, check our Odin versions page. Some older Samsung devices work better with older Odin builds.
- 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 with them.
- Install the Listed Drivers:
- Confirm all drivers listed above are installed and that your PC has been restarted since installation. 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 (add Home button on older models) 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, this 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, give it up to 8 minutes.
Video Guide for Flashing
What to Expect After Flashing Samsung Galaxy S21 5G SM-G991Q Firmware
After flashing the Samsung Galaxy S21 5G SM-G991Q firmware, you should expect a longer first boot time, a warm device, and a completely clean system state. I get a lot of comments from people who think something went wrong when it actually did not. Do not worry if things look a bit different right after the flash. Here is what is completely normal after a successful installation:
- How to know the flash was successful: Odin will show “PASS.” in green text at the top-left of the log area. If you see this, everything went fine.
- First boot takes 3 to 8 minutes, do not force-reboot the device. The operating system is setting itself up from scratch. Interrupting this is how devices end up in bootloops.
- The phone will feel warm during first boot, this is normal. It settles after a few minutes once the initial app setup is complete.
- All your apps are gone, this is expected. 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-G991Q 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-G991Q After Flashing?
A missing IMEI on the Samsung Galaxy S21 5G SM-G991Q after flashing usually indicates a corrupted EFS partition where your IMEI and carrier settings are stored. Please note that restoring an IMEI that does not belong to your original device is illegal in most regions, so only attempt this if you are restoring the phone’s original number. Tools like ChimeraTool or BFT can help you fix this. Check your local laws before proceeding.
Video Guide: How to repair IMEI
Common Issues When Flashing Samsung Galaxy S21 5G SM-G991Q
- Odin Shows “FAIL” Instead of “PASS”:
- This is usually a mismatch between the firmware region or model and your device. Confirm your exact model number in Settings › About Phone before selecting the firmware. Even a single letter difference in the model code matters.
- Samsung Galaxy S21 5G SM-G991Q Not Recognized by Odin:
- Reinstall the Samsung USB drivers. Make sure you are in Download Mode. Try a different USB cable, Odin can be sensitive to cable quality.
- KG Lock / Knox Triggered After Flashing:
- This happens when a Samsung account was still signed in before flashing, or when unofficial firmware was used. Always sign out of Samsung accounts before flashing. If KG lock is already active, a professional unlocking tool is generally needed.
- Boot Loop After Flashing:
- Enter recovery mode (Volume Up + Power) and perform a factory reset. This clears any leftover data from the previous firmware that may be causing the conflict.
Frequently Asked Questions
Q1: Will flashing the Samsung Galaxy S21 5G SM-G991Q firmware erase my data?
A: Yes, installing this software with Odin completely wipes the phone and restores it to factory settings, including the default Android 15, One UI 7 layout. Every app, photo, contact, and account will be deleted. Make sure to back up anything important beforehand, as there is no way to get this data back once the process is done.
Q2: Is this firmware compatible with other Samsung models?
A: No, this package is strictly for the Samsung Galaxy S21 5G SM-G991Q running the Samsung Exynos 2100 processor. Even a slightly different variant of the SM-G991Q might use completely different internal hardware. Flashing the wrong file can leave your phone very difficult to repair. Always verify your exact model in Settings › About Phone.
Q3: Can I downgrade from the latest version to an older firmware version?
A: While it is technically possible on certain Exynos builds, I advise against it. Rolling back can introduce security flaws and break app compatibility on Android 15, One UI 7. If the newest update is giving you trouble, leave a comment below and we can usually find a better solution than downgrading.
Q4: What should I do if I encounter an FRP lock after flashing?
A: Grab our free Android apps launcher. FRP activates on the Samsung Galaxy S21 5G SM-G991Q when a Google account remains signed in prior to flashing. This is exactly why I always recommend logging out of your Google account first, it prevents the lock from happening.
Q5: Are custom ROM options available for the Samsung Galaxy S21 5G SM-G991Q?
A: This guide only covers official Samsung stock software. Whether custom ROMs exist for the Samsung Galaxy S21 5G SM-G991Q depends on the open-source kernel support for the Samsung Exynos 2100 platform. Feel free to check our Custom ROMs page or browse the XDA Developers forum for specific custom ROM threads.
Q6: My Samsung Galaxy S21 5G SM-G991Q is not detected by Odin. What should I do?
A: Start with the drivers, reinstall the Samsung USB drivers, reboot your computer, and try again. If you are plugged into a USB 3.0 port, switch to a USB 2.0 port, as Samsung phones tend to connect more reliably to the older standard. Temporarily turn off your antivirus software. If it still fails, drop 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-G991Q?
A: Turn the phone off entirely, then press and hold Volume Up + Power together until the recovery menu loads. If you have an older Samsung phone with a physical Home button, press Volume Up + Home + Power. The recovery menu will display the build number for your Samsung Galaxy S21 5G SM-G991Q, which is useful for checking your current software version before flashing.
Q8: My IMEI shows “unknown” after flashing the Samsung Galaxy S21 5G SM-G991Q. Is my phone permanently damaged?
A: No, your phone is not broken, even though it looks scary. Just follow the IMEI repair guide in the troubleshooting section above. For Samsung phones, you should check the EFS partition for corruption first. Most importantly, do not put a SIM card into the phone until the IMEI is fully restored.
Q9: How long does it take to flash Samsung Galaxy S21 5G SM-G991Q 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 reboot after the flash takes a bit longer, usually between 3 and 8 minutes. Do not touch or unplug the phone during either phase. If the Odin progress bar seems to pause, just give it a few extra minutes before assuming something failed.
Final Thoughts on Samsung Galaxy S21 5G SM-G991Q Firmware
You now have all the tools and steps required to successfully install the official Samsung Galaxy S21 5G SM-G991Q firmware (the latest version) using Odin. If you followed the instructions closely, your phone should be running smoothly on a fresh system.
If you ran into a snag, like a specific error code or a step that did not work, leave a comment below. Please include as much detail as possible: the exact error message, where you are in the process, and what you have tried so far. I read every comment and will help you figure it out.
If this walkthrough made things easier for you, please consider sharing it. It is a great way to help someone else who might be stuck on the same problem.
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.
