[Android Head-Units] Anton TNT:
It is accessed by numeric pad (same as would for factory settings, but only entering specific code in number pad).

Code is 7788 so you must enter it in numeric pad in order to access directly to engineering mode.

Also, there are other codes accessed with numeric pad directly :

Code: 0 - Opens MCU update window (com.ts.can.CanMcuUpdateActivity)

Code: 1 - Opens some sort of window (com.ts.main.CStudy.CStudyMainActivity)

Code: 5 - Checks chip version and if matches opens some sort of LCD settings

Code: 2 - QR code that redirects to url with head units serial id that redirects to wechat

Code: 3 - Shows Phone device id?

Code: 4 - Sends signal to MCU to reboot - HARD reset just like with reset hole on unit

Code: 8 - Resets audio settings for Navi

Code: 9 - (DONT TRY THIS) Opens some sort of head unit activation window (com.ts.main.auth.AuthActivity)

Code: 6 - Sets Bluetooth id to 10000

Code: 12 - Opens a window that shows head units production id

Code: 22 - QR code that redirects to url with head units production id

Code: 5678 - Opens custom boot logo window (com.ts.logoset.LogoSetMainActivity)

Code: 8888 - Opens factory settings window (com.ts.factoryset.FsMainActivity)

Code: 4321 - Deletes files from "/mnt/sdcard/demo"

Code: 1234 - Copies files to "/mnt/sdcard/demo"

Code: 1101 - Something with screenshots

Code: 1313 - Sends signal to radio to reset

Code: 1414 - Reboots system and saves changed device settings or factory settings

Code: 1616 - Display Brightness, Contrast, Hue, Sat, Sharp, GrassToneH, GrassToneS, SkinToneH, SkinToneS, SkyToneH, SkyToneS settings (Saved to /storage/emulated/0/Ts/filter.txt)

Code: 1515 - Opens test mode window? (something for head unit activation?) (com.ts.main.auth.FactoryMainActivity)

Code: 6666 - Copies and installs some sort of APK files (maybe all default apps)

Code: 7777 - Shouldn't do anything

Code: 7788 - Opens engineering window (debugging information, you can view all logs etc.) (com.mediatek.engineermode.EngineerMode)

Code: 8877 - Opens a window where you can change all audio volume settings, boot logo, other settings (com.ATCSetting.mainui.MainActivity)

Code: 120 - Checks for system update?

Code: 2134 - Opens app info list (com.qiner.appinfo.AppListActivity)

Code: 12345678 - Sends some sort of signal to the MCU and opens some sort of tscanupdate window (com.ts.tscanupdate)

Code: 3699 - Check if some system files exists and opens tscanupdate window with some custom flags sent to it (com.ts.tscanupdate.MainActivity2)

Code: 5699 - Check if some system files exists and opens tscanupdate window with some custom flags sent to it (com.ts.tscanupdate.MainActivity2)

Code: 7758258 - Android stress-test, executes a command "monkey --throttle 500 --pct-touch 90 --pct-motion 10 -v -v 100000 >"

Code: 1111 - Opens some sort of window (Memory status real-time) (com.ts.phonestate.PhoneStateService)

Code: 140 - Closes GPS

Code: 141 - Opens GPS

Code: 123 - If DSP is supported opens alert with DSP version

Code: 0128 - Opens some sort of window (CanAllUpdateActivity)

Code: 0129 - Starts some sort of Can service (com.ts.can.CanDataLogService)

Code: 5555 - Opens a window where you can export advanced settings to SD or USB (com.ts.factoryset.FsMPModeActivity)

Code: 860 - Checks for disk

Code: 1717 - Should play some audio track

Code: 002446 - Roots head unit, installs google services, unroots head unit, reboots -> REPORTED THAT DID NOT WORKED ON ANY DEVICES