Reflashing Xiaomi Redmi S2: a complete guide with unlocking the bootloader

Xiaomi Redmi S2 (codename ysl) is a budget smartphone of 2018, which is still popular due to the ability to install custom firmware and upgrade to modern versions of MIUI or Android. However, the firmware of this device has nuances, from the mandatory unlocking of the bootloader to the risk of “bricking” if errors in the process.

In this article, you will find the most current ways to flash Redmi S2 in 2026, from official updates via MIUI Updater to manual installation via Fastboot or TWRP Recovery.

• 🔓 How to unlock the bootloader without errors (including bypassing the account binding restriction)
• 📥 Where to download the verified firmware for ysl and how to choose the version (Global, China, EEA)
• ⚙️ Step-by-step instructions for each firmware method with process illustrations
• ⚠️ Common Errors (such as anti-rollback or invalid image) and how to avoid them

Important: Redmi S2 is the default lock bootloader, which means that custom firmware installations (like LineageOS or Pixel Experience) will require official unlocking via the Mi Unlock Tool, a process that can take up to 720 hours (30 days) to first connect to an account.

1. Preparation for flashing: what to do before the start

Reflashing the Xiaomi Redmi S2 requires pre-preparedness to avoid data loss or turning the device into a brick.

1. Back up all the data. Even if you plan to upgrade without a reset (OTA), there is always a risk of failure.

• 📁 Mi Cloud (for contacts, notes, photos) – check that sync is enabled in Settings → Xiaomi account → Mi Cloud
• 💾 Local backup through Settings → Additionally. → Backup and reset → Local backup
• 🖥️ ADB Backup (for applications and their data) – command: adb backup -apk -obb -shared -all -f backup.ab

2. Check the current firmware version and device model. This is critical for choosing the right firmware file. Go to Settings → About the phone and write down:

• 📋 Version. MIUI (for example, MIUI Global 12.5.3 Stable)
• 📋 Assembly number (e.g, V12.5.3.0.REFMIXM)
• 📋 Device code – must be ysl (for Redmi) S2)

3. Make sure the battery is charged. The firmware process can take up to 30 minutes, and an interruption due to battery discharge is almost guaranteed to cause a failure. The optimal charge level is at least 60%.

⚠️ Note: If your device has previously undergone unofficial modifications (e.g., Magisk installation or modification) boot.img), Unlocking the bootloader may not work properly, in which case you will need a full reset to the factory settings before the procedure begins.

I recorded the version. MIUI and assembly number|Created a backup of the data|Battery charge ≥60%|I downloaded the necessary firmware (see section 2)|Installed Xiaomi drivers on PC (if required)|Disabled antivirus (can block Mi Flash Tool)-->

2. Selection of firmware: official vs custom

The Redmi S2 has several firmware types available for stability, functionality and installation requirements.

How to choose a version of MIUI? Official firmware for Redmi S2 are divided into:

• 🌍 Global – for the international market (Google Services support, many languages)
• 🇨🇳 China – China version (without Google, but with additional features for China)
• 🇪🇺 EEA — European version (corresponding to the GDPR, without some Xiaomi services)
• 🇷🇺 Russia – adapted for Russia (pre-installed local services)

For most users, the Global Stable is the best choice. If you want the latest innovations, go to Xiaomi.eu Weekly (an unofficial port with weekly updates).

⚠️ Warning: Installing firmware with a lower version of Android (downgrade) than the one already installed on the device may result in anti-rollback protection activated.This will lock the device at bootloader level! Always check the Android version in the firmware name (e.g, V12.5.3.0.REFMIXM — M here means Android 10).

3. Unlocking the bootloader: step-by-step instructions

Without unlocking the bootloader, you can only install official updates through MIUI Updater. For manual firmware via Fastboot or TWRP, unlocking is mandatory.

Step 1. Link your Xiaomi account to your device.

1. Go to Settings → Xiaomi Account and log in.
2. Enable Settings → Additional → Developers → Linking the Mi (Mi Unlock status) account.
3. Link the device to your account (an internet connection is required).

Step 2. Install the Mi Unlock Tool on your PC.

• 🖥️ Download the latest version of the tool from the official website.
• 🔌 Connect your phone to your PC in Fastboot mode (turn off the device, then press Volume down). + Nutrition).
• 🔓 Launch the Mi Unlock Tool, log in and follow the instructions.

Step 3. Wait for the waiting timer to finish.

When you first connect your account, Xiaomi blocks the unlock for 720 hours (30 days), this timer cannot be bypassed legally!

⚠️ Note: If you are buying a Redmi S2"Hands on hand”, make sure that the previous owner untie his Xiaomi account from the device. Otherwise, unlocking will not be possible without his login details.

1. disable two-factor authentication in your Xiaomi account.

2. Use another USB-cable (preferably original).

3. Launch the tool on behalf of the administrator.

4. Make sure that the same account is used on the phone and in the Mi Unlock Tool.-->

4. Firmware via Fastboot (Mi Flash Tool)

Fastboot is the most reliable method for installing official firmware, as it flashes through all parts of the device, including boot and recovery, and is suitable for restoring a bricked phone or a clean installation.

What you need:

• 🖥️ Windows computer (7/10/11)
• 🔌 Cable USB (original or high-quality)
• 📥 Firmware in.tgz format (download from the official website)
• 🛠️ Mi Flash Tool (last version)

Step-by-step:

1. Unpack the firmware. The.tgz file contains the partition image folder. Unpack it into the root of the C:\ drive (the path should not contain Cyrillic!).
2. Install drivers. When you connect your phone in Fastboot mode, Windows should automatically install the Android Bootloader Interface driver. If that doesn't happen, download the driver manually from the Android site.
3. Start the Mi Flash Tool. Select the folder with the unpacked firmware, then press Refresh - the device must be determined.
4. Select firmware mode: Clean all - complete cleaning (recommended when changing the version of MIUI) Clean all and lock - cleaning + lock bootloader (only for official firmware!) Save user data - data storage (not always stable)

Start the firmware.

Flash

If the process is 99% dead or there is an invalid sparse file error, try:

• 🔄 Restart your PC and phone.
• 🔌 Use the other USB-port (preferably) USB 2.0).
• 📥 Download the firmware again (possibly the file has been downloaded with errors).

💡

Fastboot erases all data on the device, including internal memory (/data). Always back up before the process begins!

5.Firmware through TWRP Recovery

Installing via TWRP allows you to flash custom firmware (like LineageOS) or modified versions of MIUI (like Xiaomi.eu). However, there is a nuance to the Redmi S2: the official TWRP may not support data encryption, so you will need to format /data after installation.

Step 1. Install TWRP Recovery.

1. Download the latest version of TWRP for ysl from the official website.
2. Rename the file to twrp.img and place it in the folder with ADB.
3. Connect your phone in Fastboot mode and execute the command: fastboot flash recovery twrp.img fastboot boot twrp.img

Step 2. Fix the firmware through TWRP.

1. Download the firmware in.zip format and place it on SD-card.
2. In TWRP, select Install → specify the firmware file.
3. Additionally, file Magisk (if root is needed) or Disable Force Encryption (if the firmware does not support encryption).
4. Run Wipe → Format Data (required for custom firmware!).
5. Reset the device.

⚠️ Note: If after installing custom firmware, the phone is stuck on startup the Xiaomi logo or reboots in a loop, then the firmware is not compatible with your version of the bootloader. Try a different build or return to the official one. MIUI via Fastboot.

6. Solving typical firmware errors

Even if you follow the instructions, you can still get errors, and the following are the most common problems and solutions for the Redmi S2:

This MIUI version cannot be installed on this device

This error occurs when you try to install firmware for another model (e.g., Redmi 6 instead of Redmi S2). Always check the device code (ysl) in the firmware file name. For example, the correct file name should contain:

ysl_global_images_V12.5.3.0.REFMIXM_20220315.0000.00_10.0_global_...

Here ysl is the device code, REFMIXM is the Global version, 10.0 is the Android version.

1. disable driver signatures in Windows (via gpedit.msc).

2. Use the Mi Flash Tool version 20180510 or later.

3. Connect the phone to the port USB 2.0 (blue) - ports USB 3.0 is sometimes a problem.-->

7.Update via MIUI Updater (without unlocking)

If you don’t need custom firmware, the easiest way to upgrade the Redmi S2 is to use the built-in MIUI Updater, which doesn’t require unlocking the bootloader and saves all the data.

How to update through OTA:

1. Open Settings → About the phone → System update.
2. Click Check Updates. If the update is available, download it.
3. After downloading, click Reboot and Update.

How to update manually (if OTA does not come):

1. Download the full service pack (.zip) from the official website (select Redmi S2 → Recovery ROM).
2. Put the file in the root of internal memory (not in folders!).
3. Open Settings → About Phone → System Update → Click on the three dots in the upper right corner → Select the update file.
4. Select the downloaded file and confirm the installation.

Advantages of this method:

• ✅ Does not require unlocking the loader.
• ✅ Stores all data and settings.
• ✅ Minimum risk of error.

Disadvantages:

• ❌ Updates come with a delay (especially for older devices).
• ❌ It is impossible to install custom or modified firmware.

8. Frequently Asked Questions (FAQ)