Only for phones with MEDIATEK processors! Not for Qualcomm Snapdragon Samsung Exynos HiSilicon Kirin etc.

MTK Engineer Mode is a secret menu on your MediaTek smartphone in which you can configure and test the Hardware and the Software of your device modifying the factory values.
You will have access to:

- Telephony
- Connectivity
- Tests and hardware settings (Camera TouchPanel Vibration Audio ...)
- Tests and Location settings
- Log and Debugging
- Software Settings
- Others

If you want to help to translate MTKEngineerMode App to your language go to: https://github.com/ZonaRMR/MTKEngineerMode-Translations

Visit the XDA thread: https://forum.xda-developers.com/android/apps-games/app-mtk-engineer-mode-t2975528