The situation when, when trying to make a call or check the balance, the message “Connection problems or incorrect MMI code” appears on the smartphone screen can take any subscriber by surprise. It is especially unpleasant when this happens with a SIM card from one of the largest operators, such as MTS. The abbreviation MMI stands for Man-Machine Interface, which means the interface between man and machine. Essentially, this is a command that you enter manually or that is sent automatically when you press the call button.
There is no need to panic at such a moment, since in the vast majority of cases the problem is of a software nature and can be easily solved without a visit to the service center. The error can occur both when entering USSD commands (for example, *100#), and when dialing a number normally. Let's take a look at why your Androidsmartphone refuses to cooperate with the operator's network and what steps need to be taken to restore the connection.
Main causes of errors on the device
Before taking active steps to eliminate the failure, it is necessary to understand the nature of its occurrence. Most often, the problem lies not in the physical breakdown of the SIM card, but in a conflict of software protocols. The operator's network sends a certain signal that the phone cannot process correctly or interprets as incorrect. This may be due to a temporary malfunction of base stations MTS in your area.
Another common reason is the incorrect operation of the smartphone modem itself. The internal radio software may freeze while waiting for a response from the network. In such cases, even a full signal does not guarantee the ability to make a call. It is also worth considering the human factor: accidentally entering an extra character into a command or using outdated USSD codes that the operator has already taken out of service.
⚠️ Attention: If the error appears only when you try to call a specific number, perhaps the problem is not in your phone, but in the status of the subscriber's number or forwarding settings.
Sometimes the culprit itself becomes SIM card The contacts on the chip may have oxidized, or the card may have received microdamage when removed from the tray carelessly. In rare cases, the conflict occurs due to installed third-party call management or spam blocking applications that intercept system calls and modify them before sending them to the network.
Basic troubleshooting methods
The easiest and often effective way to solve the problem is to reboot the device. This action allows you to reset all temporary caches of the radio module and re-register with the operator’s network. Turn off your smartphone, wait 10-15 seconds and turn it on again. After the system boots, try making a test call or entering the balance check command.
If a simple reboot does not help, the next step should be to double-check the physical condition of the SIM card. Turn off the phone, remove the tray and carefully inspect the chip. Scratches, chips, or dark spots may indicate damage. Gently wipe the contacts with a soft, dry cloth to remove any dust or grease that is preventing normal contact.
☑️ Diagnosing a problem with the MMI
Make sure that the SIM card is installed in the slot correctly, observing the orientation of the corner cut. In dual-SIM devices, try moving the card MTS to another slot. Sometimes one of the slots may be unstable due to software network priority settings. It also makes sense to temporarily disable the second SIM card in the settings to eliminate a conflict between two active communication profiles.
Setting up a network and selecting an operator manually
Automatic network selection in Android settings does not always work correctly, especially in areas of poor reception or at the border of coverage of different communication standards (2G, 3G, 4G). Forcing manual online registration MTS can help bypass the incorrect MMI code error. To do this, go to the phone settings menu.
Find the section responsible for mobile networks. The path may differ depending on the model of your smartphone, but usually it looks like this: Settings → Connections → Mobile networks → Telecom operators. Disable the "Select automatically" option. The phone will begin searching for available networks, which may take several minutes.
| Action | Expected result | Execution time |
|---|---|---|
| Disable auto selection | List of available operators | 1-2 minutes |
| Selecting MTS manually | Registration in the home network | 30-60 seconds |
| Checking the call | Successful connection | Instantly |
| Return auto selection | Stable operation in roaming | 1 minute |
When the list appears on the screen, select your operator from it - MTS. Wait for registration confirmation. If after this the error disappears and calls continue, you can leave the setting in manual mode or try returning the automatic selection, since the network profile may have already been updated. This method is especially relevant for users who often move between regions.
What to do if the network is not located?
If, after disabling automatic selection, the list of operators is empty or MTS is missing, try moving closer to a window or to an open space. Also make sure Airplane Mode is not turned on in Settings or 5G Only mode is activated if coverage in your area is poor. In some cases, temporarily switching the network type to “2G Only” for forced registration helps.
Resetting the network settings to factory settings
A more radical, but safe for personal data, method is resetting the network settings. This procedure will not delete your photos, contacts, or apps, but will return all connection settings to their out-of-the-box state. This includes Wi-Fi, Bluetooth settings and, most importantly, mobile communication settings.
To perform this operation, go to the system settings. Find General Settings or System, then select Reset. In the list of options, find “Reset network settings” or “Reset Wi-Fi, mobile data and Bluetooth settings.” Confirm by entering your screen unlock PIN if prompted.
⚠️ Note: After resetting your network settings, you will need to re-enter the passwords for all saved Wi-Fi networks and re-pair your Bluetooth headsets and watches.
After rebooting, the phone will try to receive the latest settings from the operator MTS automatically. This usually takes a few minutes. Check if you receive SMS with Internet parameters and try to make a call. If the problem was caused by an incorrect change in any hidden network parameters, this method should completely eliminate it.
Checking balance and blocking by the operator
Sometimes the cause of the MMI error is trivial - a negative balance or temporary blocking of services by the operator. Even if it seems to you that there is money in the account, it is worth double-checking the information using official methods, not through USSD commands, which may not work. Use the mobile application My MTS or your personal account on the website.
Make sure that there are enough funds in your account to make calls and that communication services are not suspended. Also check to see if the Call Barring service is activated, which may have been accidentally enabled through the phone menu or upon request from support. Sometimes the operator carries out technical work that temporarily limits the ability to use some services.
Use the “My MTS” application to check the balance and status of services if USSD commands give an error. The application works over the Internet and does not depend on the voice communication channel.
If you have recently changed your tariff plan or connected new options, the error may be due to an incomplete service activation process on the server side. In this case, waiting for 15-30 minutes or registering online again often solves the problem. Do not forget that tariff conditions and available services may change, so check the latest information in the official application.
Solving the problem through the engineering menu
For advanced users, it is possible to diagnose the radio module through the Android engineering menu. This method allows you to check the connection status and force a network configuration update. Be careful when using this method and do not change settings that you do not know.
To enter the engineering menu, open the “Phone” application and enter a special command. For many devices based on processors MediaTek the code is used ##3646633##, and for processors Qualcomm — ##4636##. If the code is suitable for your model, a special menu with several tabs will open.
##4636##Go to the “Phone Information” section. Find the "Mobile network" item and try switching the network type. For example, change NR/LTE/GSM to LTE Only or vice versa, and then return the original value. There may also be an “Update” or “Refresh” button, clicking on which initiates re-registration on the network. After manipulations, be sure to reboot the device.
The engineering menu is a powerful diagnostic tool, but changing unknown parameters can lead to a complete loss of communication. Use it only to reset network settings.
When a SIM card replacement or a service visit is needed
If none of the software methods helped, and the “Invalid MMI code” error continues to appear, the problem may be hardware. SIM cards have a limited service life and can fail over time, especially if they have been used for several years. Old samples of SIM cards may not work correctly in modern 4G and 5G networks.
The best diagnostic method in this case is to test your SIM card in another phone. If the error is repeated in someone else’s device, it means that the problem is definitely in the card or in the network coverage in this location. In this case, you need to contact the nearest communication store MTS with your passport for a free SIM card replacement while maintaining your number and balance.
- 📱 The error persists in another phone - the problem is in the SIM card.
- 📶 Everything works in another phone - the problem is in your smartphone (modem, software).
- 🛠️ Replacing the SIM card did not help - the phone needs to be diagnosed in the service.
In rare cases, the radio module of the smartphone itself is faulty. This may be due to a fall, moisture, or a manufacturing defect. If replacing the SIM card and completely resetting the settings did not work, and other SIM cards in your phone also do not work, you should contact an authorized service center for professional diagnostics.
Frequently asked questions (FAQ)
Why does the MMI error appear only when checking the balance?
This may indicate that a specific USSD command is outdated or blocked on the operator’s side. Try using alternative codes or checking the balance through the mobile application.
Does the case affect the connection error?
Yes, some metal or too thick cases can shield the antenna signal, which leads to unstable communication and errors when sending commands. Try removing the case and checking the connection.
Can a virus cause an invalid MMI code error?
Theoretically, malware can block calls or intercept commands, but in practice this happens extremely rarely. More often, the reason lies in the network settings or the state of the SIM card.
What to do if the phone says “Not registered on the network”?
This is a more serious error than MMI. Try manually selecting an operator, resetting network settings, or test the SIM card in another device. The SIM card may need to be replaced.
Will resetting settings delete my photos and contacts?
No, the “Reset network settings” function only affects connection settings (Wi-Fi, Bluetooth, mobile network). Your personal files, applications and contacts will remain safe.