Xiaomi Mi S2 firmware: a complete guide from unlocking to installing custom software

Xiaomi Mi S2 (codename siris) is a popular smartphone of 2018, which is still actively used due to its reliability and the ability to install current firmware. However, the process of firmware of this device has nuances related to the unique architecture of Qualcomm Snapdragon 625, protection Mi Anti-Rollback and the features of unlocking the bootloader. In this article, we will analyze all the methods of firmware – from official updates via MIUI Updater to install custom builds such as LineageOS or Pixel Experience.

It’s important to understand that the Mi S2 firmware requires preparation. For example, switching from Android 8.1 to Android 10 can block a device due to the Anti-Rollback 3 mechanism if you do not follow the procedure. We will describe each step in detail, including unlocking the bootloader, choosing the correct version of the firmware and solving typical errors like EDL Mode or “blinking red indicator”.

This article is relevant for all Mi modifications. S2 (including a global version M1803E6G Chinese M1803E6T) And it takes into account the latest changes in Xiaomi's bootloader unlock policy (2026). If you're a beginner, start with the official method, TWRP bypassing the Anti-Rollback.

1. Firmware Preparation: What to Do Before Starting

Before you start firmware, make sure that all the preliminary steps are followed, and neglecting them can lead to a "brick" (complete failure) of the device.

• 🔋 Battery charging level must be at least 60%. S2 may go into mode EDL, exiting from which will require special equipment.
• 📋 Backup: Save data from internal memory (photos, contacts, messages) and firmware via Fastboot or TWRP erase user files.
• 🔗 Cable. USB — Use the original Xiaomi cable or certified USB 2.0 Cheap cables can cause data transmission errors.
• 💻 Drivers – Install Mi Flash Tool and Qualcomm drivers to work properly in Fastboot mode.

Also check the current firmware version in the Settings → About Phone → MIUI version. If your Mi S2 is running MIUI 10 or older, installing custom firmware will require a rollback to MIUI 9 followed by unlocking the bootloader.

2. Unlock the bootloader on Xiaomi Mi S2

The Xiaomi Mi S2 bootloader is locked by default. To install unofficial firmware or modified cores, it must be unlocked through the official Mi Unlock Tool. The process takes up to 720 hours (30 days) of waiting if the Mi Account is not tied to the device in advance.

Step-by-step:

1. Link your Mi Account to your phone: go to Settings → Xiaomi Account → Sync and enable all options. Wait 7 days (minimum time for new accounts).
2. Download the Mi Unlock Tool (version no lower than 5.5.224.24 for the Mi S2).
3. Transfer the phone to Fastboot mode: turn off the device, press Volume down + Power before the hare appears in the hat.
4. Connect the Mi S2 to your PC, launch the Mi Unlock Tool and log in. Press Unlock. If a Couldn't unlock error appears, try again in 24 hours.

Once successfully unlocked, the phone will display Unlocked in Fastboot mode, and you can now install TWRP or flash the device through Fastboot.

⚠️ Note: If you unlock the bootloader but haven’t installed custom software within 30 days, Xiaomi can automatically block it again. TWRP or official firmware through the Mi Flash Tool.

3. Ways of firmware Xiaomi Mi S2: which one to choose?

There are three main Mi S2 firmware methods, each suitable for different purposes:

For most users, Fastboot is the best option, allowing you to install any official firmware, including Stable, Developer or regional versions. Castom firmware is recommended only for advanced users, as it can contain bugs (for example, broken). IR-blaster NFC assemblies).

4. Firmware through Fastboot: step-by-step instructions

This method is suitable for complete flashing of the device, for example, when switching from Global ROM to China ROM or recovering from a software failure.

• 📱 Unlocked loader (see section 2).
• 🖥️ PC with Qualcomm and Mi Flash Tool drivers installed.
• 📁 Firmware in.tgz format for Mi S2 (You can download the Xiaomi Firmware Updater).

Instructions:

1. Unpack the archive with firmware in a folder without Cyrillic characters (for example, C:\MiS2_Fastboot).
2. Transfer the phone to Fastboot mode (clamp Volume down + Power).
3. Connect the Mi S2 to your PC and launch MiFlash.exe. In the program, click Select and specify the path to the firmware folder.
4. Select firmware mode: Clean all - complete cleaning (recommended when changing the firmware region); Clean all and lock - cleaning + locking the bootloader (only for official firmware!); Save user data - saving user data (not always stable).

Press Flash and wait until it is completed (usually 5-10 minutes).

If you are running an older version of MIUI (e.g. from MIUI 12 to MIUI 11), pre-disable Anti-Rollback via the command:

fastboot oem edl

Without this step, the device will lock at the boot stage with the Anti Rollback Check Fail error.

5. Installation of TWRP and custom firmware

Unofficial firmware (such as LineageOS 18.1 or Pixel Experience 12) will require custom TWRP recavators. It is important to use a version adapted specifically for the Mi S2 (codename siris).

Steps of TWRP installation:

1. Download the latest version of TWRP for siris from the official website.
2. Transfer the phone to Fastboot and connect to the PC.
3. Open the command line in the folder with platform-tools and do: fastboot flash recovery twrp-3.7.0_9-0-siris.img fastboot boot twrp-3.7.0_9-0-siris.img
4. After downloading to TWRP, swipe to allow modifications (if you request).

Now you can stitch custom firmware.

1. Copy. ZIP-the firmware file for internal memory or SD-map.
2. In TWRP, select Wipe → Advanced Wipe and select Dalvik, Cache, System, Data.
3. Press Install, select. ZIP-file and confirm installation.
4. After completion, swipe GApps (if required) and Magisk (for root rights).

If the device stopped turning on after a failed firmware, try to transfer it to EDL Mode using a test point on the motherboard.

1. Open the back cover (a mediator and a hair dryer will be needed to soften the glue).
2. Find the test point next to the battery (designated as EDL or TP).
3. Lock it to the "ground" (body) and connect it USB-The phone will be called Qualcomm. HS-USB QDLoader 9008.

💡

If the camera stopped working after firmware, check the firmware version. Some custom ROMs for the Mi S2 require a separate patch for the camera (for example, ANXCamera or GCam with a config for the Snapdragon 625).

7. Update firmware without data loss

If you want to upgrade the Mi S2 without resetting, use the official MIUI Updater or OTA method via TWRP.

1. Download the full service package (.zip) for your model with Xiaomi Firmware Updater.
2. Move the file to the root of the internal memory.
3. Reboot to TWRP and select Install → select ZIP → Swipe to confirm.
4. After installation, clean Dalvik/Cache and restart.

This method saves user data but does not guarantee stability. If you have lags after the update, reset via Settings → Additional → Restore and Reset.

💡

When updating through TWRP Never use the "Wipe Data" option, it will result in the loss of all files (Dalvik/Cache) conflict prevention.

FAQ: Frequent questions about the firmware Xiaomi Mi S2