Google Nexus devices are famed for their stock Android experience, but experienced Android users will improve this by tinkering with the device settings, UI (user interface), built-in apps and themes, and by installing custom ROMs and tweaks, kernels and over-clocking. However, in order to use such tools, the device's bootloader must be unlocked.
Here is a step-by-step guide to unlock the bootloader on your Nexus 4 device running Android 4.1.2 Jelly Bean OS:
Note: This guide is compatible only with the LG Nexus 4 and will not work on any other device. Verify your device's model number by navigating to Settings > About Phone.
How to Unlock Bootloader on Nexus 4 Running Android 4.1.2 Jelly Bean
Step 1: Download and install the Android SDK (Software Development Kit) from here, which includes the necessary drivers for Nexus 4 on your computer.
Step 2: Download Fastboot, which is needed to unlock the bootloader.
Step 3: Extract or unzip the Fastboot.zip file to a desired location on your computer (for instance your desktop). Now, you should see a folder named Fastboot on the desktop with four files inside it.
Step 4: Power off the Nexus device and boot into fastboot mode through a button sequence: press and hold the Volume down and Power buttons together until the display turns on and shows the "Start" message on the screen in large green letters.
Step 5: Connect your Nexus phone to the computer with a USB cable, and wait until Windows finishes installing the necessary drivers. It is advisable to use the USB port at the back of the computer, particularly if you are using a desktop, as the front panels may get loose and create issues.
Step 6: Click Start > All Programs > Accessories > right-click on command prompt and then choose Run as administrator. If you are running Windows 8, just right-click on the extreme bottom left corner of the taskbar and then choose "Command Prompt (admin)" in the pop-up window.
Step 7: Execute the following steps in sequence at the command prompt to unlock the Bootloader:
- Browse to the Fastboot folder you got in Step 4. For instance, if the Fastboot folder is in drive C: on the computer, then enter cd C:Fastboot in command prompt and hit Enter. This command will take you directly to the folder's location.
- Enter fastboot devices in the command prompt and press enter. If your Nexus 4 device is detected correctly, it will show the device ID in command prompt. If nothing shows up, verify that you installed the correct drivers in step 2.
- Finally, enter fastboot oem unlock in command prompt to unlock the bootloader. You will see a prompt on your phone asking you to confirm the action. Just click Yes to confirm. Please note that this process will wipe the data on your phone. So, make sure that you have backed up all your important data before doing this step.
- The phone will now reboot, and once the home screen comes up, you are all set to tweak your phone.
NOTE: To relock the bootloader just repeat the entire procedure from step 5 to step 8, but in step 8.3 enter fastboot oem lock. This will re-lock the bootloader.
The Bootloader on your Nexus 4 phone is now successfully unlocked, and you are all set to begin installing custom ROMs and tweaks on it.
[Source: Android Central]