Blocking the bootloader on Xiaomi Redmi 4X: safe methods and pitfalls

Xiaomi Redmi 4X (codenamed santoni) remains a popular device among customization enthusiasts, but not everyone knows how to properly return it to factory status — especially when it comes to locking the bootloader. Unlike unlocking, which requires official permission through the Mi Unlock Tool, the reverse process is often surrounded by myths and risks. This article will examine all the working ways to lock the bootloader on the Redmi 4X, including the official method through Mi Flash, alternative solutions for custom firmware, and explain why some instructions from the Internet can turn your smartphone into a “brick”.

It's important to understand that locking a bootloader isn't just a "backstop" after unlocking it, it requires considering the current state of the device (MIUI version, firmware type, anti-rollback status), and having the right tools, such as trying to lock a bootloader on a device with custom firmware installed (like LineageOS or Pixel Experience) without first returning to stock MIUI leads to a permanent lock of the device (hard brick) in 90% of cases.

This article will be useful to those who:

• 🔄 Wants to bring Redmi back. 4X (b) fully factory-produced before sale.
• 🔒 Faced with the requirement to lock the bootloader for updating through OTA.
• 🛠️ Experimented with custom firmware and wants to return to official software.
• ⚠️ Received a security risk warning due to unlocked bootloader.

1.Why locking the bootloader on Redmi 4X is not a trivial task

At first glance, it may seem that locking the bootloader is just running a fastboot oem lock command in the terminal. However, in practice, it is much more complicated. Xiaomi has implemented several layers of protection that complicate this process:

• 🔐 Anti-Rollback Protection (ARB): A mechanism that blocks rollbacks to older versions of firmware. at Redmi 4X ARB activated from the version MIUI 9.5 and higher Attempt to block the bootloader on the firmware with a lower version ARB lead to brick.
• 📦 Firmware type: On devices with custom Recovery (for example, TWRP) modified boot.img locking the loader without returning to the stock MIUI impossible.
• 🔄 Unlock status: If the bootloader has been unblocked informally (for example, through exploits), the official Mi Flash tool may refuse to block it back.

Moreover, Xiaomi does not provide official documentation on the bootloader lock, and support in such cases usually responds with the standard phrase: “We do not recommend unlocking, therefore, we do not support blocking,” which leaves users with risks and forcing them to look for solutions in forums where outdated or dangerous instructions are often found.

⚠️ Note: If your device was bought with hands and already has an unlocked bootloader, be sure to check the version before locking. MIUI through settings → The phone. → Version. MIUI. If the version is older than the one installed now, you will need to first perform a downgrade in compliance with the rules. ARB.

2.Preparation of the device: what to do before the lock

Before you start locking, you need to get the Redmi 4X to a state where the process will go smoothly.

Make sure the version MIUI This is the last official one for your region.|

Return stock recavers (remove TWRP or OrangeFox)|

Remove root rights (Magisk, SuperSU) and return stock boot.img|

Check Anti-Rollback (ARB) status via fastboot|

Back up the data (locking will reset the device)|

Charge the battery to at least 60% |

Install official Xiaomi drivers for PC

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To check the current status of ARB, connect the device to your PC in fastboot mode and follow the command:

fastboot getvar anti

In the answer, you'll see something like anti: 3 or anti: 4. This number indicates the current version of ARB. You can only lock the bootloader on firmware with an ARB equal to or higher than the current one! For example, if you have anti: 3 and you try to flash MIUI 9.2 (where ARB=2), the device locks forever.

Another critical point is the stock recavator, and if you have a TWRP installed, you have to replace it with the original one.

fastboot flash recovery stock_recovery.img


fastboot boot stock_recovery.img

Where stock_recovery.img — Stock Recovery File for Your Version MIUI, You can download from the official Xiaomi website or from the forum XDA Developers.

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If the device does not boot after returning to the stock recavator, try resetting via fastboot erase userdata, which will delete all user data, but will restore the system to work.

3.Official method: locking through Mi Flash Tool

The most reliable (but not always affordable) method is to use the official Mi Flash Tool, which is suitable for devices that:

• 📱 They're on stock firmware. MIUI (modificationless).
• 🔓 Unlocked through the official Mi Unlock Tool.
• 🔄 Have a firmware version compatible with the current status ARB.

Step-by-step:

1. Download the Mi Flash Tool from the official Xiaomi website (version no lower than 2018).
2. Download the stock firmware for Redmi 4X (select the version that fits your region: Global, China, EEA).
3. Unpack the firmware in a folder without Cyrillic symbols on the way.
4. Run the Mi Flash Tool on behalf of the administrator.
5. Connect your phone in fastboot mode (clip Volume Down + Power).
6. In the Mi Flash Tool, click Select and specify the folder with the unpacked firmware.
7. Select firmware mode: clean all – complete cleaning (recommended). clean all and lock – firmware + bootloader lock (not available in all versions of Mi Flash).

Flash

If your Mi Flash Tool version doesn’t have a clean all and lock option, you can try an alternative way:

1. Switch the device in clean all mode.
2. After successful MIUI download, restart to fastboot.
3. The command is: fastboot oem lock
4. Confirm the lock on the device screen (if you receive a request).

Decision:

1. Swipe stock firmware through Mi Flash in clean all mode.
2. If the device doesn’t boot, try resetting through the stock Recovery (Loudness up + Power → Wipe Data).
3. If nothing helps, EDL.

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Before blocking the bootloader, always check the hash amounts of the downloaded firmware. Fake or corrupted firmware files are a common cause of bricks!

6 What to do if things go wrong: Recovery from a brick

If the Redmi 4X stopped turning on after trying to lock, don’t panic – in most cases the device can be restored.

• 🟢 Soft brick: The device vibrates when you press the power button, but does not load (hangs on the Mi logo).
• 🔴 Hard brick: The device does not respond to buttons, the screen is black, but when connected to a PC is defined as Qualcomm HS-USB QDLoader 9008.
• ⚫ Full brick: PC-detected, no charging response. Recovery is only possible via eMMC soldering.

For soft brick:

1. Try going to fastboot (Loudness down + Nutrition).
2. If possible, run the stock firmware through Mi Flash.
3. If not, try stock Recovery (Loudness up + Power) and run Wipe Data.

For hard brick:

1. Make sure that the device is identified as Qualcomm 9008 in Device Manager.
2. Download the firmware in.mbn format for santoni.
3. Use Mi Flash Pro in EDL mode (Authorized Account is required).

If you have a full brick, self-recovery is unlikely, in which case contact a service center with equipment to work with eMMC (for example, EasyJTAG or Medusa Pro).

⚠️ Warning: Do not try to stitch the device in the hard brick state through a regular fastboot - this can permanently damage the boot partitions. EDL service-tool.

7. Myths and truths about locking a bootloader on Xiaomi

There are many tips on how to block a bootloader on Xiaomi on the Internet, but not all of them are relevant or safe.

Myth 1: “Blocking the bootloader improves security”

✅ It's true, in part, that locking does protect against some attacks (like fastboot), but:

• 🔒 It does not protect against exploits in the kernel or applications.
• 📱 Modern versions MIUI have built-in protection even with the unlocked bootloader (for example, Mi Protect).
• 🔄 Blocking may prevent you from receiving OTA-Updates if the device has been modified.

Myth 2: “You can lock the bootloader on any firmware”

❌ As mentioned, the only way to lock is to lock the stock. MIUI compatible ARB. Trying to do that on:

• 📦 Bone firmware (LineageOS, AOSP) → brick-and-mortar.
• 🔙 The firmware is older than the current version ARB → brick-and-mortar.
• 🔧 Modified firmware boot.img → bootloop.

Myth 3: “Xiaomi officially supports bootloader locking”

❌ Xiaomi provides the Mi Unlock Tool, but does not guarantee the reverse process.The official documentation does not mention the blocking, and the support refuses to help in such cases.

Myth 4: “Blocking the bootloader resets the IMEI”

✅ True, but not always. IMEI stored in the nvram and persist partitions, if the lock is correct, IMEI It will stay in place, but if:

• 🔧 You've been stitching through modified sections.
• 📥 Used unofficial firmware.
• ⚡ There was a failure during the lockdown.

→ then IMEI Always back up these partitions before manipulating the bootloader!

8. FAQ: Answers to frequent questions