How to Solve Connection Problem or Invalid MMI code Issue?

If you are an Android phone user, then you could have come across a message like “Connection problem or invalid MMI code” on dialing a USSD code.

You can see this error when you are about to check your account balance or performing any function designed by your Sim service provider, like adding a voucher to run a USSD code. It is a serious problem which can affect your phone resulting in imposing some restriction while sending or receiving text messages, calls, checking account balance and so on.

Solutions to solve the issues:

1. Enter Safe Mode

To enter the safe mode and to find out the problem interfering with the network operation of your phone. Follow the instructions given below to enter the safe mode:

  • Switch off your mobile phone.
  • Hold down the Power Button by keep tapping on the menu button or the left button of the home key.
  • You will be navigated to a safe mode logo at the bottom of the screen.

To check whether the error is solved:

  1. Enter the prefix code you were trying before with the dialer to check it works or not.
  2. If the solution works, then it is been caused an app on your android phone.
  3. Reboot your mobile and remove the recently installed applications.

2. Check Network Settings

Solving this “Connection Problem or Invalid MMI Code” problem, this method will help to fix this problem.

  • Open the Settings option on your device.
  • Select the Network Connection option.
  • Tap on the Mobile Networks.
  • Search for the Network Operators.
  • Select your prefered Network from the list.
  • Finally it over, restart your mobile phone and check for the problem is solved or not.

3. Restart your Phone Several Times

Open the Network settings on your phone, then hold down the power button and the home button together until your phone turns off. Turn it on back and do this several times.

4. Modify Prefix Code

This is an alternative way to solve your connection problem. You have to just add a comma(,) at the end of your prefix code. This forces the operation to look for the error and you can also add “+” after your prefix code.


These are simple methods to solve connection problem or invalid MMI code issue, from your mobile phone. If you have any doubts regarding this issues, you can ask them in the comment section.