How To Fix Connection Problem or Invalid MMI Code Error

Every now and then, you may run into the Connection Problem or Invalid MMI Code pop up error on your Android device.  This generally happens when a user is trying to send an Man-Machine-Interface code, aka MMI code.  What is a MMI code you ask? It’s those funny codes you enter on your dialer that includes an asterisk (*) or hash (#) characters, like calling #BAL on your Verizon Wireless phone to check account balance, or sometimes it’s just a prefix code you enter before a phone number.  If the Connection Problem or Invalid MMI Code problem is driving you nuts, we got a few solutions that should solve your issue.

Simple Reboot

Simply turn off your phone (press the Power button for a few seconds) and reboot again, see if that helps in fixing the connection problem or invalid MMI code on your phone.  This method 1 may sound simple, but sometimes that’s all it takes to get rid of the invalid MMI code error!

Reboot in Safe Mode

By using your phone in safe mode, you can better troubleshoot your phone since it will run just the stock Android programs.  By eliminating all other apps running in the background, you can test to see if the invalid MMI code problem persists without other apps running through app disabling. Safe mode will disable pre-installed apps and services that came with the phone.

So to solve the Connection Problem or Invalid MMI Code issue, let’s reboot in safe mode.

To reboot in safe mode or enter safe mode, follow these steps:

  1. Turn off your device.
  2. Press and hold the power button to turn on, continue holding the power button until the logo screen appears. Release the power button once you see the logo. 
  3. Press and hold the volume down button until the reboot is finished.
  4. You should see “Safe mode” at the bottom left corner of your screen (left of the screen).

A combination with the Home button (like those selected Samsung Galaxy phones) might be needed for this process. Contact your phone manufacturer to verify or check the manual that came with the phone. Once in safe mode, try entering the MMI you were using before to see if the problem persists.  If you don’t have issue sending the text messages at this point, then most likely a culprit app that may have recently installed is causing the conflict.  You can start by uninstalling the most recent app and go from there.

Add a plus sign (+) or comma (,) to the code

Try adding a comma at the end of your code and dial again, a USSD code for example, if you were trying to dial *1234 then try dialing *1234, you can add a comma by holding the asterisk (*) button for about 3-5 seconds. Check if the error is gone after you add a comma at the end of the prefix. 

Or try adding a plus (+) sign after the asterisk (*) sign in your code. This process forces the operation to look for the invalid MMI code error. For example, if you were dialing *1234 then try dialing *+1234 you can get the plus (+) plus sign by holding zero for about 3-5 seconds.  The plus sign should get rid of the error message and allow the call to go through. This process forces the operation to look for the USSD codes error.

Check Network Settings

You could be getting the Connection Problem or Invalid MMI Code error because you are not getting reception.  Try setting your wireless provider, go to:

  1. Settings
  2. Network Connection
  3. Mobile Networks
  4. Navigate to Network Operators
  5. Search Networks and select your wireless provider

You might want to try this method 2 a few times before giving up on it.  It might take a few tries before it connects to the available networks. If the network operator search does not find your carrier or service provider, then you might want to check your SIM card for possible problems that may be interfering with the network or SIM authentication.

Check Sim Card

If you have a dual sim phone, you have two choices here.

  1. Disable on of your SIM cards and activate only the SIM that you plan on using to send the MMI code.  The phone may not be using the correct SIM card if you had both SIM cards running together.
  2. Under your phone’s dual SIM settings, find the voice call settings by tapping on the menu.  There it should give you an option to select with SIM card to use or “Always ask”, choose that “Always Ask” option.  When you try to dial the MMI code, the phone will prompt you and ask which SIM you want to use, that why you will have the option to select the correct SIM card.

If you have a traditional single SIM phones, try something simple like pulling your SIM card and blowing on it, wiping it down a little, and plug it back in.  See if that will re-establish connection.

Turn on SMS over IMS

This step is for the tech geeks and we won’t get into details on how to do it since any wrong move using this method could destroy your phone, or just cause more headache to undo.  It basically involves you using the Android secret code *#*#INFO#*#* or dial 4636 in the dialer aka *#*#4636#*#* to enter the Android Testing Menu or information mode, this is where professional technicians go to geek out on your phone information or device information.  You can run ping test and activate radio and turn on SMS over IMS here that could solve your “Connection Problem or Invalid MMI Code” problem .  If you really want to try this method, feel free to google “how to turn on SMS over IMS“.


As you can see, there are several ways on how you can fix the MMI code error. You can enter Safe mode or restart your phone, add some prefix code, check the network settings, check your SIM card and turn on IMS over SMS are just a few. If you still have a network connection or invalid MMI code error on your Android phone after trying the procedures many times, you might need to visit a local shop and have your phone checked properly by an authorized technician. They should be able to find a way to fix the problem. There might be some hardware issues that’s preventing your device to recognize the network operators for mobile networks network.

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George Tsay

Executive editor in charge of The Droid Guy since 2012. Coordinates a group of more than 10 editors and writers based around the world as they cover the latest and greatest products in consumer technology. Grew up and lives in Southern California. Go Bruins. Go Padres. Go Chargers. Find me on Twitter

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