By default the Intel® AMT MEBx password is:
If the password was changed and you don't know it, you should reset the password; there are two different ways to perform this action.
Option 1: You have Intel® AMT version 10.x and higher:
Some manufacturers include in his BIOS the option of resetting the Intel® AMT MEBx password and settings; you need to enter to the BIOS settings repeatedly pressing the corresponding key during the boot process, this changes depending on the manufacturer. The key appears during the boot process.
Inside the BIOS Settings look for an option that allows you reset your Intel® AMT MEBx password and settings (commonly inside Advanced or Management Engine category), if you found it you should perform that action and after a restart, the Intel® AMT MEBx password should be admin again.
If you don't see that option follow the instructions for Intel® AMT version 9.x and earlier..
Option 2: You have Intel® AMT version 9.x and earlier:
You should reset the CMOS. The CMOS is a non volatile memory that saves settings of your hardware.
To reset the CMOS, you need to follow the next step:
Turn off the device and unplug it from the energy
Open the system cover
Locate and remove the coin-cell battery
With the computer disconnected from the energy, press the power button for 1 minute to drain the system of any residual power
Reinstall the coin-cell battery
HP devices have additional steps:
Locate the CMOS Button and press it for at least 5 seconds
Change the jumper position from the pin 1 and 2 to the pin 2 and 3
Replace the system cover, connect the computer and turn it on until you listen to a beep
Turn off the computer and bring back the jumper to the original position.
After doing all previous steps, is time to install the system cover, connect the computer and turn it on. Your Intel® AMT MEBx password should be admin again.