Immediately after installing a firmware update on a Samsung smartphone, the device may begin to rapidly discharge, slow down the interface, or even lose some of its usual functions, which forces the owner to look for a way to roll back the system to a stable version.
It is important to immediately understand that the “Uninstall update” button in the settings menu does not always work. In most cases, it only resets application settings or the cache, but does not roll back the system itself. For a full downgrade (downgrade), you will need to use a computer and specialized software.
This procedure affects the deep levels of the device’s file system. Before taking active steps, it is necessary to assess the risks and prepare all the tools. Wrong actions can lead to loss of warranty or turning the phone into a “brick.”
Why you should remove the update and what risks exist
The decision to roll back the firmware is often dictated by real need. After installing the new build, users notice that the performance has deteriorated, and the heating of the case has become more noticeable even during simple tasks. Sometimes new functions simply do not take root, making use battery optimization worsened, and the heating of the case became more noticeable even during simple tasks. Sometimes new features just don't catch on, making use One UI less comfortable.
However, the process is not without dangers. The most important threat is the bootloader being blocked due to the counter being triggered Knox. If you try to install unofficial firmware or compromise the integrity of the partitions, many services, including Samsung Pay and Secure Folder, will stop working permanently.
⚠️ Attention: The flashing procedure will void the official manufacturer's warranty if software tampering is detected. Service centers may refuse free repairs.
In addition, there is a risk of losing personal data. When switching to an older version of Android, the system often requires complete formatting of the data section, since new file structures may be incompatible with old encryption algorithms.
Preparation for the system rollback procedure
The success of the operation depends 90% on the quality of preparation. You will need a personal computer or laptop running Windows, since the main tool - the app Odin - does not have versions for macOS or Linux without the use of virtual machines.
Be sure to check the battery level of your device. It should be at least 60-70%. If the phone turns off while data is being written to the partition system or boot, restoring it will be extremely difficult, and in some cases impossible, without a hardware programmer.
It is also critically important to find the correct firmware version. You need a file that has a build index lower than the currently installed one. To check the current version, go to Settings → About phone → Software information and write down the build number.
- 📱 Complete backup of all contacts, photos and documents to external media or to the cloud.
- 💻 Installation Samsung USB Driver drivers to your computer to correctly identify the device.
- 🔌 Original USB cable to ensure a stable connection without loss of data packets.
- 📂 Downloaded stock firmware specifically for your model (SM-G991B, etc.).
☑️ Ready for flashing
Searching and downloading official firmware
Finding the correct file is a non-trivial task. The official Samsung website does not provide direct links to older versions of the software for downloading by ordinary users. You will have to use third-party aggregator resources, such as SamMobile, SamFw or Frija.
When selecting a file, pay attention to the region (CSC). If you bought a phone for the European market, the firmware for the USA or Vietnam may not work or lead to incorrect operation of the radio module. Look for the region code that matches your SIM card.
⚠️ Attention: The interfaces of firmware aggregator sites change frequently, and download speeds may be limited. Check the file hashes, if provided, to ensure the integrity of the download.
After downloading, the archive usually has the extension .zip or .rar. It needs to be unpacked. Inside you will find several files with extensions .tar or .tar.md5. These are the images of the partitions that we will record.
How to decrypt the firmware code?
The firmware code usually looks like this: G991BXXU5DVK3. The first characters (G991B) are the device model. The following (XX) are the region. The letter U/C/A indicates the build type (official/service). Number 5 - Android/Binary version. The last three characters (DVK) are the release date (year, month, day). To rollback, the Binary version must be less than or equal to the current one, but the release date must be older.
Instructions for flashing firmware via Odin
The app Odin is a standard tool for Samsung service engineers. It allows you to download images directly into the phone's memory, bypassing the standard Android bootloader. Download the latest stable version of the utility (for example, Odin3 v3.14.4).
Run the app as an administrator. Now you need to put your smartphone into Download Mode. For modern models without a Home button, press the Volume Down and Power buttons simultaneously when the phone is turned off, then when a warning appears, press Volume Up.
Connect your phone to the computer with a cable. In the Odin app, the field ID:COM should be highlighted in blue or yellow, indicating a successful connection. If this does not happen, reinstall the drivers or try another USB port.
| Slot in Odin | Firmware file | Partition description |
|---|---|---|
BL |
BL_*.tar.md5 | Bootloader |
AP |
AP_*.tar.md5 | System partition and kernel |
CP |
CP_*.tar.md5 | Modem and communication |
CSC |
CSC_*.tar.md5 | Regional settings (with data clearing) |
Distribute the files into the appropriate slots by clicking on the buttons and selecting the unpacked images. Pay special attention to slot CSC. Use a file starting with CSC_, not HOME_CSC_. The first option will perform a complete data reset, which is mandatory when downgrading, the second will only update the settings, which can cause errors.
Go to the Options tab and make sure that the checkboxes are only opposite Auto Reboot and F. Reset Time. No other items, such as Re-Partitioncan be touched unless you are using a PIT file, which is prohibited for the average user.
If the process is stuck at the "NAND Write Start" or "SetupConnection" stage, do not panic. Try disabling your antivirus and firewall while installing the firmware, as they may block writing to the device ports.
Press the button Start to start the process. The progress bar will show the recording status. Do not under any circumstances disconnect the cable until the message PASS! appears in the green field. After this, the phone will reboot automatically.
Using the CSC file instead of HOME_CSC is critical when downgrading Android, as this will ensure that old configuration files that may conflict with the new (old) system are cleared.
Alternative methods and factory reset
If flashing the firmware seems too difficult, you can try a less radical method - resetting to factory settings through the recovery menu (Recovery Mode). This will not delete the update itself, but will remove conflicting user data and cache.
To enter Recovery mode, turn off the phone and hold down Volume Up + Power (on new models, you may need to connect to a PC via USB). In the menu, select the item Wipe data/factory reset using the volume buttons and confirm with the power button.
This method helps in cases where the problem is not caused by the update itself, but by the “garbage” left after its installation. However, if the reason lies in code errors in the new version of Android, this method will not help restore stability.
⚠️ Attention: Resetting via Recovery will delete all photos, contacts and applications from the internal memory. Make sure you have an up-to-date backup before starting the procedure.
There are also applications like Samsung Smart Switchthat allow you to reinstall the software. However, they usually offer only the current version of the system, so they are useless for uninstalling (rolling back) updates.
Frequent errors and ways to solve them
One of the most common problems is an error FAIL! (Auth) in the Odin app. This means that you are trying to install firmware with a lower version of the bootloader (Binary) than what is currently on the phone. Samsung blocks such actions to protect against vulnerabilities.
In this case, it is impossible to remove the update programmatically. The only way out is to wait until the manufacturer releases a new stable branch, or look for service firmware (Engineering ROM), which is extremely risky and requires deep knowledge.
Another error - FAIL! (PIT). It occurs if the partition structure does not match. The solution is simple: do not use the Re-Partition option and make sure that the firmware is designed exactly for your model (for example, you cannot flash S21 on S21 Ultra).
- 🚫 Connection error: check the cable and USB 3.0 port (blue connector).
- 🚫 Hash error: the firmware file was downloaded broken, you need to download again.
- 🚫 FRP Lock: after flashing you will need to enter the Google account that was synchronized earlier.
What is FRP Lock?
FRP (Factory Reset Protection) is protection against theft. If you reset your phone or reflash it, the system will require you to enter the password for your last Google account. Without this, the phone will remain locked, even if the firmware was successfully installed.
Is it possible to remove the update without using a computer?
Unfortunately, using standard Android tools it is impossible to remove a system update and roll back to the previous version without a PC. The “Uninstall update” button in the menu only works for system applications, not for the OS itself.
Will Odin erase all my data on the phone?
Yes, if you use a CSC file (not HOME_CSC), the internal memory will be completely formatted. All photos, contacts and messages will be deleted. The external SD card is usually not affected, but it is better to remove it before starting.
Why does the phone take a long time to turn on after flashing the firmware?
The first boot after recording a new system image can take from 5 to 15 minutes. At this time, applications are optimized and new system files are created. Do not interrupt this process, even if the screen seems frozen.
Will the warranty return after the official firmware?
If you are using the official firmware and the Knox counter has not been increased (0x0), then it is impossible to visually distinguish the phone from the new one. However, in the service documentation there may be a trace of the last connection to the service software.
What to do if the phone went into a cyclic reboot?
Try to enter Recovery Mode and make a Wipe Cache Partition. If it doesn’t help, repeat the firmware procedure via Odin, making sure that the correct files and modes are selected. In the worst case, the board will need to be replaced.