Error: Connection problems or invalid MMI code. What to do?

Today we’ll talk about a fairly well-known error that users of smartphones based on the Android operating system may encounter. When sending USSD requests, the message “Connection problems or an invalid MMI code” may appear on the smartphone screen. The message may also look like “Connection problem or invalid MMI code” or even in English – Connection problem or invalid MMI code.

The error on the device screen looks something like this:

In English:

The question is – what is MMI? MMI or Man-Machine Interface is a special code used to generate USSD requests, which provides interaction between the subscriber and the operator’s service applications. Sometimes a failure occurs, which leads to the indicated error. What to do? There are several possible solutions, we will talk about them in more detail.

Send USSD request again

Suppose that you decide to find out the balance of the account by sending a request * 100 #, as a result of which you receive an error, you do not observe any communication problems. Try sending the USSD request again, and after a while, if that doesn’t work, again. Perhaps this is a problem on the side of the carrier.

Turn airplane mode on and off

Flight mode, as you probably know, allows you to turn off all device communications. Turn on airplane mode literally for 5-10 seconds, then turn it off again so that your smartphone finds a network.

Then send the USSD request. Most likely, it will work.

Reboot your smartphone

In general, turning on and off the flight mode should be enough to solve communication problems. However, there may be a problem in the software of the smartphone – say, there was some kind of failure. In order to return the device to its previous form, just reboot it. Or turn it off and on again – to whom it is more convenient.

After switching on, check the device for errors..

Change network type

Try changing your network type. Let’s say you use networks in Auto mode. You need to try changing the type of network to 3G or even 2G – for a while, then you can return everything to its original state.

Go to settings.

Find the “Wireless Networks” section (the example uses a Huawei smartphone, on devices of other companies the interface may vary slightly).

Tap on the line “Mobile Network”.

Click Preferred Network Type.

Change the type of network. Ideally, you should use a mixed type of network (“Auto”), most likely, you have it installed. Choose a different type of network, wait a minute and return to Auto mode..

Then send the USSD request. If that doesn’t help, select a different type of network and try sending a USSD request with it..

If you use “Only 4G”, in this case you will not be able to send USSD requests in any case, switch to the mixed type of network mode (“Auto”).

Make sure the carrier network is selected.

This may be caused by some kind of failure. You need to choose the coverage of your service provider. To do this, go to the same section “Mobile Networks” and select “Operator”.

Wait for the download and select your carrier’s network. Although it’s better to use automatic network selection (the switch at the top of the screen).

The procedure may help, especially if you are roaming..

Disable VoLTE

All in the same settings of mobile networks, try disabling VoLTE calls if this feature is supported by your device (thanks for the idea to a user named Oleg).

After try to specify the USSD command.

Download in safe mode

There is a small chance that the appearance of an error is associated with the operation of an application. How do you make sure of this? Enough to enable safe mode.

In this mode, Android launches only system applications, so you can immediately understand whether the application is in the application or not..

Try adding a character to a USSD request

Some users claim that adding a character to a USSD request can help. For example, a comma.

USSD request works, oddly enough.

SIM card issues

An error occurs if there are problems with the SIM card. For example, it is very old and it is time to replace it, or you incorrectly cut it. In such cases, USSD requests will not work at all, you need to replace the SIM card.