Xiaomi Redmi 9T firmware: official and custom methods with unlocking the bootloader

Xiaomi Redmi 9T (codenamed lime) remains a popular budget smartphone even years after its release. However, over time, users face the need to reflash the device — whether to upgrade to a fresh version of MIUI, install custom firmware like LineageOS or Pixel Experience, or to restore performance after a crash. In this guide, we will analyze all the current methods of firmware, including official and informal methods, as well as the nuances of unlocking the bootloader, which often become a stumbling block for beginners.

It’s important to understand that firmware isn’t just an “air update”; it’s a deep interference with the system files of the device that can both bring the Redmi 9T to life and turn it into a “brick” when you do the wrong thing. We’ll go into detail on preparing, choosing the right firmware (including stable, beta and custom builds), and tools like the Mi Flash Tool, ADB and Fastboot.

If you’ve never flashed a Xiaomi smartphone before, start with the section on unlocking a bootloader — it’s a must for most methods.Savvy users can immediately go to installation instructions via Fastboot or TWRP. And if your goal is to just upgrade MIUI without risk, we’ll show you how to do it safely through the built-in update menu.

1. Firmware Preparation: What to Do Before Starting

Redmi 9T firmware requires not only the firmware and the computer itself, but also the proper preparation of the device, and neglecting this stage is the main reason for the "bricking" of smartphones.

• 🔋 Battery charge at least 60%. The firmware may take up to 30 If the device turns off in the process, the consequences will be fatal. 80-100%.
• 📱 Backup: Firmware erases all user data, including photos, contacts and messages. Use Mi Cloud, Google Drive or local copying on your PC.
• 🖥️ Drivers and PC software. Install Mi. PC Suite or drivers ADB/Fastboot Without them, the computer will not recognize the smartphone in firmware mode.
• 🔗 Cable USB. Use the original Xiaomi cable or certified cable USB Type-C: Cheap cables can interrupt the connection, causing a failure.

Pay special attention to unlocking the bootloader. On the Redmi 9T, it is locked by default, and without unlocking you will not be able to install custom firmware or even official through Fastboot. The process takes up to 7 days (due to Xiaomi's policy), so start in advance. More on this is in the next section.

Also check the current version of MIUI in settings (Settings → About Phone → MIUI Version) to avoid problems with anti-rollback, a security mechanism that blocks rollbacks on older versions of firmware. For example, if your Redmi 9T runs MIUI 14, you won’t be able to install MIUI 12 — the device will lock.

2. Unlock the bootloader on Redmi 9T: step-by-step instructions

Unlocking the bootloader is a must for most firmware methods, except for upgrading through OTA or Recovery (without resetting data). Xiaomi has made this process more complicated to protect users from accidental errors, but you can get around the limitations. Here's how to do it:

1. Link your Mi Account to your device: Go to Settings → Xiaomi account and log in. Enable data sync and confirm the link via SMS or email.
2. Activate debugging on USB unlock OEM: Open the Settings. → About the phone and 7 times click on the version MIUI, To turn on the developer mode. Go back to Settings. → Additionally. → For developers and include: 🔧 Debugging by USB 🔓 Unlocking OEM (It may be called a factory unlock)

Request permission to unlock:

• Download the Mi Unlock Tool and launch it on PC.
• Sign in with the same Mi Account as you do on your phone.
• Connect Redmi 9T in Fastboot mode (turn off the phone, then press Power + Volume down).
• In the tool, press Unlock. If you see a message that you need to wait, wait. SMS-notifications (usually) 3-7 days).

Important: after unlocking the bootloader, all data on the phone will be erased, and Widevine protection will be deleted. L1 (viewable HD-content from Netflix, Disney+ etc.) may decrease to L3, It's an irreversible process, so weigh the pros and cons.

If the Mi Unlock Tool gives you a "Couldn't unlock" or "Device not supported" error, try:

• 🔄 Reconnect the phone to another USB-port (preferably) USB 2.0).
• 📱 Reboot your smartphone and PC.
• 🛠️ Use a different version of the Mi Unlock Tool (e.g., from here).

Linked to the Mi Account to the device|Debugging is on. USB|Unlocking enabled OEM|Drivers installed ADB/Fastboot|Phone's loaded on 60%+-->

3. firmware selection: official MIUI vs custom builds

Before you can flash the Redmi 9T, you need to decide on the type of firmware. Each option has pros and cons:

For Redmi 9T, the official firmware is divided into:

• 🌍 Global (EEA) — Europe, with support for all languages and Google services.
• 🇨🇳 China – without Google services, but with a lot of features MIUI.
• 🇮🇳 India – optimized for local market, may contain regional restrictions.

Castom firmware requires installation via TWRP or Fastboot. Popular options for lime include:

• 📱 LineageOS 20 (Android 13) – stable, but without branded chips Xiaomi.
• 📱 Pixel Experience – as close as possible to Google’s “pure” Android.
• 📱 ArrowOS – Balance between customization and performance.

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Before installing custom firmware, check if it supports VoLTE and VoWiFi for your carrier. Without this, 4G/LTE calls will not work.

4. Fastboot Firmware: Official Method with Mi Flash Tool

This method is suitable for installing an official MIUI (including downgrade, if anti-rollback allows) or recovering the device after a failure.

• 🖥️ Windows PC (7/10/11).
• 🔗 Cable USB (original).
• 📁 Firmware in.tgz or.zip format (download from the official website).
• 🛠️ Mi Flash Tool (last version).

Step-by-step:

1. Unpack firmware: Downloaded archive (for example, lime_global_images_V12.5.1.0.RJQMIXM_20230315.0000.00_11.0_global_1234567890.tgz) Unpack into a folder without Cyrillic symbols on the way (for example, C:\MIUI\lime).
2. Launch the Mi Flash Tool on behalf of the administrator: Click Select and specify the path to the folder with the unpacked firmware.
3. Connect your phone in Fastboot mode: Turn off Redmi 9T. Squeeze the power. + Volume down until the Fastboot logo appears.Plug in to PC.Mi Flash Tool should appear COM-port.
4. Select firmware mode: 🔄 Clean All – Complete cleaning (recommended in case of failures). 🔄 Clean All and Lock - Cleaning Up + Locking the bootloader (for the sale of the phone). 🔄 Save User Data – an attempt to save data (not always working).

Start the firmware:

• Press Flash and wait until it is completed (5-10 minutes).
• The phone will reboot automatically.

If the Mi Flash Tool is giving an error called "Invalid Image":

• Make sure that the firmware is suitable for lime (not limein or limeeea).
• Make sure that the path to the firmware folder does not contain spaces or Cyrillic.
• Try another version of the Mi Flash Tool (such as the Mi Flash Pro).

5. Firmware through Recovery: Update without data loss

This method is suitable for updating MIUI without resetting if:

• 📲 You already have an official firmware installed.
• 🔄 You are upgrading to a newer version (not downgrade!).
• 🔓 The bootloader can be blocked (unblocking is not necessary).

Instructions:

1. Download firmware for Recovery: On the official website, select the version marked Recovery (.zip file). Rename the file to update.zip and place it at the root of the phone's internal memory.
2. Run the update: Go to Settings → About Phone → System Update. Click on the three dots in the top right corner and select Select Firmware File. Specify the path to update.zip and confirm installation.

Wait until it's finished:

• The phone will reboot to Recovery and start installing.
• Don't interrupt the process! It can take 10-15 minutes.

If the update through Recovery does not start:

• 🔋 Check the battery charge (should be) ≥50%).
• 📁 Make sure the file is update.zip Not damaged (check checksum) MD5).
• 🔄 Restart your phone and try again.

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Updating through Recovery is the safest method, but it only works for official firmware and does not allow you to downgrade the MIUI version.

6. Install custom firmware through TWRP

To install LineageOS, Pixel Experience or other custom firmware, you'll need TWRP, custom recovery, which is more complicated than Fastboot, but it's more powerful.

Step 1: Installation of TWRP

1. Download the latest version TWRP for lime from the official website (file) twrp-3.7.0_9-0-lime.img).
2. Rename the file to twrp.img and place it in a folder with ADB (e.g., C:\platform-tools).
3. Connect your phone in Fastboot mode and execute the command: fastboot flash recovery twrp.img fastboot boot twrp.img

Step 2: Firmware through TWRP

1. Download custom firmware (e.g. lineage-20.0-20231010-nightly-lime-signed.zip) and, if necessary, GApps (for Google services).
2. Put the files on. SD-card.
3. V TWRP execute: 🧹 Wipe → Advanced Wipe (tag Dalvik, Cache, System, Data). 📁 Install → select the firmware file → Swipe to Confirm Flash. 🔄 Repeat for GApps (if necessary). 🔧 Reboot System.

Common errors when running through TWRP:

• 🚫 "Failed to mount /data" — Execute Format Data in TWRP (erase!).
• 🚫 "Error 7" - firmware is not suitable for your model (check the codename lime).
• 🚫 Logo getting stuck – try stitching vendor and firmware separately.

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Once you have custom firmware installed, it can take 10-15 minutes to start the first run. Don't panic or turn off the device!

7 Solving Typical Errors When Firmware Redmi 9T

Even if you follow the instructions, you can get errors, and let's look at the most common ones and how to fix them.

If the IMEI is missing or the mobile network is not working:

1. Check if the /nvram folder is saved (if not, restore the backup via TWRP).
2. Refuse modem and firmware separately through Fastboot:

If Wi-Fi or Bluetooth does not work after installing custom firmware:

• Make sure that the firmware supports your model (lime).
• Scroll down the vendor from the official firmware:

8. Frequently Asked Questions (FAQ)