The Samsung Galaxy A51 arrived with Android 10 out of the box and is upgradable to Android 12. These versions of the Android operating system on the Samsung A51 come with the bootloader locked, meaning you are not able to install custom firmware simply by flashing it with Samsung’s proprietary Odin software. While that has annoyed many Samsung A51 owners, thankfully you do not need to run a command in the command line with Fastboot to OEM unlock; you can instead unlock via the GUI. As usual, when you unlock the bootloader on the Samsung A51, you will void the warranty. And you do not need to unlock the bootloader to install official firmware builds.

The following tutorial demonstrates how to OEM unlock the Samsung SM-G991U bootloader.

Smartphone operating systems come with a bootloader (also known as a boot manager or bootstrap loader). The bootloader is the program responsible for booting the operating system. Sometimes this bootloader is locked by default, while other times it can come unlocked already. With an unlocked bootloader, you can install custom firmware. In today’s world, this is most often relevant to the Android operating system, and that certainly is the case when it comes to Samsung smartphones in particular. Samsung smartphones don’t come with the bootloader unlocked, but they also don’t make bootloader unlocking an arduous process. This is excellent news for those who do wish to install custom firmware because some manufacturers require the use of software exploits to unlock bootloaders.

Tip: How to Download Samsung Firmware with Free Update Tools

How to Unlock Samsung A51 Bootloader

You can unlock the bootloader on most Samsung smartphones by booting into Download Mode and selecting the option to unlock the bootloader, called Device Unlock Mode, from the menu. Here is how to do that:

Note: You need to connect your Samsung A51 smartphone to the internet via Network & internet > Internet. Alternatively, you can search for the WiFi network you want to connect to by using the search field via the Settings Menu.

1. Press the Power button to turn on the Samsung A51 device.

2. Enable the Developer Options Menu on the Samsung A51 device. See this tutorial for enabling the Developer Options menu on Samsung smartphones: How to Unlock Developer Options Menu and Enable USB Debugging Mode on Android.

Warning: Unlocking the bootloader usually causes the data to be wiped on the smartphone. So make sure you have backed up your data before continuing.

3. Boot the Samsung A51 smartphone into Download Mode. See this tutorial for booting a Samsung smartphone or tablet into Download Mode: How to Enter Download Mode on Samsung Smartphones and Tablets.

4. From the Warning screen that lets you know that a custom OS can cause critical problems on the smartphone and its installed applications, long-press the Volume Up button.

5. From the Unlock Bootloader screen that tells you if you unlock the bootloader you will be able to install a custom operating system on the smartphone, press the Volume Up button.

Note: If the device shows you a message letting you know that all data will be deleted before the bootloader can be unlocked, press the button to confirm you understand this.

Once the smartphone has rebooted, you can look into installing the custom ROM via root access or custom recovery you wanted to install. Here is the root method: How to Root Galaxy A51 on Android 12, 11, 10.