Fix Connection Problem or Invalid MMI Code

It is quite common for Android users to face a connection problem or the invalid MMI code on their devices every so often. This can be really annoying because it simply means that you won’t be able to send any text messages or make any calls until this error is fixed.

The MMI code, also known as the Man-Machine Interface code is a complex combination of the digits and alphabetical characters which you enter on your dial pad along with the * (asterisk) and # (hash) in order to send a request to the providers for checking the account balance, activating or deactivating the services, etc.

This MMI code error occurs because of many reasons such as SIM authentication issues, weak carrier providers, wrong position of the characters, etc.

To solve this issue, we have jotted down a list of ways to fix the connection problems or the invalid MMI code. So, let’s get started!

Fix Connection Problem or Invalid MMI Code

1. Restart your device

Simply reboot your device and hope for better results. Often this trick resolves all the common issues. The steps to reboot/restart your phone are as follows:

1. Long-press the power button. In some cases, you may have to press the volume down + home button until a menu pops up. It is not necessary to unlock your phone to do this process.

2. Now, select the restart/reboot option among the list and wait for your phone to restart.

Check when the code error is still occurring.

2. Try rebooting to the safe mode

This step will cut off all the third-party apps or any external software running in the background disturbing your phone’s functioning. It will help your device to troubleshoot the issue by only running the stock Android programs. Also, it is quite simple and easy to do this trick.

Steps to turn on the safe mode:

1. Press & hold the power button of your device.

2. From the options, tap on Restart.

3. On your display, you will see a pop-up asking you if you want to Reboot to safe mode, tap on OK.

4. Your phone will be booted to the safe mode now.

5. Also, you’d be able to see the safe mode written at the bottom-left corner of your home screen.

Also Read: Fix Common Problems with WhatsApp

3. Make changes in the prefix code

You can simply fix the connection Problem or the invalid MMI code on your device by modifying and changing the prefix code. All you need to do is put a comma at the end of the prefix code . Adding a comma will force the operator to overlook any error and perform the task.

We have listed down two different ways to do so:


Supposedly, the prefix code is *3434*7#. Now, put a comma at the end of the code, i.e.*3434*7#,


Instead, you can add the + symbol after the * sign i.e. *+3434*7#

4. Activate the radio and SMS over IMS

Turning on the SMS over IMS and activating the radio can also help out in fixing this issue. Perform the following steps to do so:

1. Open your dial pad and type *#*#4636#*#*. You don’t necessarily need to press the send button as it will automatically flash the service mode.

2. Tap on service mode and click on either Device information or Phone information.

3. Press the Run Ping test button and then select the Turn Radio Off button.

4. Select Turn on SMS over IMS option.

5. Now, you just have to simply reboot your device.

Also Read: How to Uninstall or Delete Apps on your Android Phone

5. Keep a check on network settings

You might want to check your network settings if your signal is weak and unstable. Your phone longs for a better signal because of which it tends to shift constantly between 3G, 4G, and EDGE , etc. A little tweaking here and there will hopefully fix your issue. Following are the steps to do so:

1. Go to the Settings.

2. Navigate to Network Connection and tap on it

3. Now, tap on the Mobile networks option and look for the Network operators.

4. Finally, search the network operators and tap on your Wireless provider.

5. Repeat this process for another 2-3 times.

6. Reboot/restart your device and hopefully, it will start working again.

6. Check your SIM card

Finally, if nothing really works, take a look at your SIM  card, maybe it is the one creating problems. Mostly, your SIM card is damaged because of continuous pulling out and reinsertion. Or, maybe it was cut roughly. Whatever the reason may be, your SIM card is probably corrupt. We recommend changing and getting a new SIM card in this kind of situation before it is too late.

For the ones using a dual SIM smartphone, you have to choose between the two:


Deactivate one of the SIM cards and enable the one that you’re using to send the MMI code. Sometimes your phone may not use the correct SIM card if you have both of them performing together.


1. Go to the Settings and find SIM cards and mobile networks.

2. Find the phone’s dual SIM settings and then tap on the Voice call Settings.

3. A pop-up list will appear, asking you to choose between Always Use SIM 1, SIM 2, or Ask every time.

4. Select Always Ask option. Now, while dialing the MMI code, your phone will ask you which SIM you want to use. Select the correct one for proper results.

If you own a single SIM card device, try pulling out and reinserting your SIM card after cleaning and blowing on it. See if this trick works.

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It can get a little pesky if the connection problem or invalid MMI code error pops up every time you dial a prefix code. Hopefully, these hacks will help you out. If your phone is still creating a problem, try contacting your service provider or customer care service for better guidance.