To flash ROMS and upgrade your Android device manually, you have to unlock the bootloader of your device. To unlock the bootloader for your Nexus 6P phone, you will have to turn on the developer options, connect your device to your computer and use fastboot (and adb as well) to run some commands and unlock the bootloader.
Please note that when you unlock or lock your bootloader, it will erase all the user data. It’s like doing a factory reset; so you want to back up everything. Also know that having your phone’s bootloader unlocked means that it is vulnerable and the system won’t be able to check for corruption. You will even get a warning during boot that says:
Your device software can’t be checked for corruption. Please lock the bootloader. Visit this link on another device: g.co/ABH. Press Power To Pause.
So, only unlock the bootloader if you know what you are doing. Just use it to flash a ROM and then lock it again immediately.
Here are the steps to unlock and lock Android bootloader in Nexus 6P phone:
In Your Phone
- Enable the developer options by going to Settings > About Phone and repeatedly tapping on the build number 7 times.
- From the new Settings that appear (System > Developer options) make sure that it is turned on along with OEM unlocking and USB debugging.
- Connect the phone with a wire to your computer and give it the permission if it asks for it.
Make sure that you have installed abd and fastboot that comes with Android Studio. If you don’t want to install Android Studio, then use this simple ADB, Fastboot and Drivers 15 second installer by xda-developers. Also, add adb and fastboot to the command prompt so that it makes your job running the commands simple.
In Your Computer (and phone for confirmation)
- Go to run and type in cmd to access the command prompt.
- To make sure that everything is good type adb devices and you will see your phone under the List of devices attached.
- Type adb reboot-bootloader
- To Unlock the Bootloader, enter the command: fastboot flashing unlock
To lock it, enter the command: fastboot flashing lock
- Use the volume keys to navigate and power button to confirm the action on your phone.
- Type fastboot reboot to restart.