ZTE Z431 hard reset

You can reset your ZTE device's password: Turn off your phone, then turn it on. Select emergency dial. Input *983*987# in emergency dial-up pad. It will restore factory settings and your personal data will be erased.
Master Clear/Reset
ZTE Z431 unlock password master clear

From the home screen, select Main Menu > Settings > Security Settings > Master Clear

The Master Clear function will clear all user data and reset the phone to factory default settings. The Master Reset function will only reset the phone to factory default settings.
If your ZTE 431 phone is frozen
Remove the back cover.
Lift the end of the battery near the bottom of the phone to remove it. Reinsert and switch on the phone.

ZTE AT&T Z431 Phone Password

A password can protect your phone and help prevent unauthorized use. When the
phone is password protected, it will ask for the password every time the phone is
turned on. Password protection is disabled by default, and the default password
is 0000.

General advice: Before you buy a new cell phone or new tablet, please try the following procedure to repair your device in a software way. First charge your battery, backup your important data if possible and in most cases take out SIM and SD card before doing factory reset. It is impossible to recover your data after doing a hard reset, so online backup is always important. For all of your data, a backup should be done on an external device, hard drive, raid system or media. With or without insurance, if your cell phone lost, damaged or stolen at least your invaluable data is backed up in a safe place. If you are about to sell your phone and you want to wipe your personal data, or if your phone affected with virus you have to do a hard reset. In some cases, you can delete the forgotten password or lock pattern from your device as well. All information is for devices with stock based ROMs. If you are using rooted device, always back up your EFS folder first, containing your IMEI info, etc.! Please also note, that a hard reset operation will not unlock your mobile phone's SIM lock or network lock, but it will remove the unlock pattern, remove the user password or PIN password (NOT the SIM card's 4 digit PIN code). Also note that the firmware version will not be affected in any way, it will not be downgraded, it will remain the same you are using and if you have rooted your device, root privileges remain also unaffected.