You are trying to check your balance, activate a service or find out the IMEI of a device by typing a special combination of characters, but instead of a response from the operator, a scary message appears on the screen: “MMI error” or “Connection problem or invalid MMI code.” This situation is familiar to many users of smartphones based on Android and can arise at the most inopportune moment, when you urgently need to find out the account balance.
In fact, there is no need to panic ahead of time, since MMI code (Man-Machine Interface) is just an interface for interaction between a person and a machine, which for some reason could not correctly process your request by the network. Most often, the problem lies not in the breakdown of the phone itself, but in the peculiarities of the operation of virtual operators, failures in roaming, or a software conflict with the network settings of the provider.
In this article we will analyze in detail why your smartphone refuses to execute the command, and we will provide a step-by-step guide for restoring the functionality of the service code dialing function. We will look at methods from a simple network restart to more complex manipulations with call settings that will help you regain control over the management of communication services.
What is an MMI code and why does it stop working
First, it is worth understanding the technical essence of the problem. MMI codes are special sequences of characters starting with an asterisk and ending with a hash (for example, *100#), which are sent directly to the mobile operator's server to perform certain actions. Unlike regular USSD requests, which require a response from the network, some MMI commands are processed locally or require a specific data exchange protocol that can be broken.
The main reason for the error is that the phone cannot establish a reliable communication channel with the operator's call center at the time the request is sent. This often happens when using eSIM or virtual numbers, where the network architecture differs from traditional physical SIM cards. Also, the failure can be caused by outdated modem software inside your Androiddevice.
⚠️ Attention: If the error occurs only when dialing a certain code (for example, to check the balance), and other combinations (like
*#06#for IMEI) work correctly, the problem is most likely located on side of the mobile operator, and not in your phone.
Sometimes the smartphone security system itself blocks the sending of such requests if it considers them potentially dangerous or if the call settings prohibit outgoing connections of a certain type. Understanding what exactly is blocking the signal is the first step to successful troubleshooting.
Before making complex settings, try simply turning Airplane mode on and off - this will often reboot the network module faster than completely rebooting the phone.
Basic methods for troubleshooting network failure
The simplest and most often ignored way to solve the problem is a simple reboot of the network interface. Many users immediately dive into deep settings, forgetting that a temporary failure in registering a SIM card on the network can be resolved by a simple reconnection cycle. You need to go to settings and find the SIM card management item.
Disable your SIM card in the settings menu, wait about 10-15 seconds, and then activate it back. Wait for the network and signal strength icons to appear. After that, try entering USSD command again. If this does not help, perform a full reboot of the device to clear the temporary cache of network services.
- 📱 Reboot the smartphone in the standard way through the power menu.
- 🔄 Disable and enable the SIM card in the section
Settings → Connections → SIM card manager. - ✈️ Activate Airplane mode for 30 seconds and then disable it.
These actions help in 80% of cases when the error is caused by a temporary “freeze” of the operating system network stack Android. If, after a reboot, the “MMI Error” message appears again, then the problem is deeper in nature and requires intervention in the call settings.
Setting a prefix for outgoing calls
One of the most effective technical methods for bypassing MMI code blocking is to add a special comma prefix to the dialed combination. This trick forces the phone to pause briefly before sending the request, which sometimes allows the network to correctly identify the type of request and process it without error.
To use this method, you need to open the Phone app and go to dial a number. Instead of standard input, for example, *100#, type ,,*100# (two commas before the code). A comma in telephony means a pause, and adding two such characters creates the necessary delay before sending the command to the operator’s server.
,,*100#This method is especially relevant for subscribers of virtual operators, such as Tinkoff Mobile, SberMobile or Yotathat use the infrastructure of other networks. Sometimes it is necessary to experimentally select the number of commas: one, two or even three, depending on the speed of registration in the network of your current location.
⚠️ Attention: Do not put spaces between commas and an asterisk. The command must look cohesive, otherwise the phone will perceive it as a regular text input, and not as a service request.
If adding commas helped, you can save this number to contacts with the pause characters already entered, so that in the future you do not have to manually enter them each time. This will create a kind of “shortcut” for quick access to the operator’s services without causing system errors.
Adding a pause (commas) before the code changes the timing of sending the request, which often bypasses protocol errors at the interface between the phone equipment and the base station.
Changing the network type and preferred communication mode
Sometimes The MMI error occurs because the phone is trying to send a request through a network type that does not support USSD commands correctly at the moment. For example, in areas of unstable coverage 4G/LTE voice and service requests may be lost or routed incorrectly.
Try to force switch the network mode to 3G or even 2G. Although these standards are outdated, they often provide a more stable channel for transmitting service signals and USSD requests. Go to the menu Settings → Connections → Mobile networks → Network mode and select the option “3G only” or “2G/3G (auto)”.
| Network mode | Stability MMI | Internet speed | Recommendation |
|---|---|---|---|
| 5G / LTE | Low (in weak signal areas) | High | For normal use |
| 3G (WCDMA) | High | Medium | To send MMI codes |
| 2G (GSM) | Maximum | Low | If 3G is not available |
After switching the mode, wait about a minute for the phone to re-register with the tower network of a different standard. Then try the command again. If the request was successful, you can return the settings back to LTE/4Gas the problem could have been a one-time problem.
It is worth noting that in some modern smartphone models, especially in global versions of Chinese brands, the network type selection menu may be hidden. In this case, you will have to use the engineering menu or special applications to manage the network, but this is a more advanced level of intervention in Android system.
How to enter the engineering menu to select a network?
Dial the code ##4636## in the phone application. The testing menu will open. Select “Phone Information”, then under “Set up preferred network type” select GSM only or WCDMA only. Be careful not to change other settings in this menu!
Resetting the mobile application and network settings
If simple methods do not work, it is possible that the phone software has accumulated errors that are preventing the communication module from working correctly. In this case, it is recommended to reset the mobile application or network settings entirely. This action will not delete your personal files, photos or contacts, but will return the network settings to the factory state.
First, try clearing the cache and data of the Phone application (dialers). Go to Settings → Applications → Phone → Storage and click the “Clear cache” button and then “Clear data”. After this, reboot your device. This often solves the problem if the failure is caused by a conflict in the dialing interface.
A more radical, but effective method is to completely reset the network settings. This procedure will delete all saved Wi-Fi passwords, paired Bluetooth devices, and mobile network settings, including hotspots. APN. However, it is guaranteed to eliminate any software conflicts that cause the MMI error.
- 🗑️ Go to
Settings → System → Reset settings. - 📶 Select “Reset Wi-Fi, mobile data and Bluetooth settings.”
- ✅ Confirm the action and wait until the process is completed.
After the reset, the phone will require you to re-set up the Internet and connect to wireless networks. Be sure to check whether your operator's access point settings have been adjusted correctly, as sometimes you have to enter them manually after a reset.
☑️ Checklist before resetting the network
Features of working with virtual operators and roaming
Separate Attention should be paid to users of virtual operators (MVNO). These providers do not have their own towers and rent capacity from major market players (MTS, Megafon, Tele2, Beeline). When roaming or when switching between partner networks, desynchronization often occurs, leading to an error MMI code.
If you are roaming, make sure that the data and voice call service is activated on the operator's side. Some tariff plans block USSD requests abroad for security reasons or due to technical limitations of partner networks. In this case, the only solution is to use the operator’s mobile application or personal account on the website.
⚠️ Attention: Tariff conditions and availability of services in roaming change frequently. Always check the latest information about the availability of USSD commands in your operator's application before traveling abroad.
For subscribers of operators such as Tinkoff or Sber, classic USSD codes may be unstable by default. The developers of these services initially rely on managing services through Internet channels. Therefore, if the persists error (persists), the best solution would be to install a proprietary application that duplicates all the functionality of MMI codes in the graphical interface.
It is also worth checking whether the “Call Barring” function is activated on your phone. Sometimes users accidentally activate barring of all outgoing calls, which also blocks service requests. You can remove this ban in the call settings by entering a PIN code, which by default is often equal to 0000 or 1234, if you have not changed it.
For virtual operators, using an official application is a more reliable way to manage services than a set of USSD codes, especially in unstable network conditions.
Frequently asked questions (FAQ)
Why does the *#06# code work, but the balance code gives an error?
The code *#06# is processed locally on the device and reads the IMEI from the phone’s memory, without requiring access to the operator’s network. Balance codes are network requests (USSD) that require an active and correct communication channel with the provider's server, where the failure occurs.
Could an MMI error be a sign of a virus on the phone?
In rare cases, malware can block network functions or intercept calls. However, in 99% of cases, the MMI error is related to network settings, SIM cards, or temporary operator failures. It is recommended to check your phone with an antivirus if other oddities are observed in the operation of the system.
What to do if nothing helps and the error does not disappear?
If you tried resetting the network settings, changing the mode to 3G and adding commas, but the problem remains, the SIM card itself may be damaged. Try inserting it into another phone. If it works there, the problem is in your smartphone (the modem may need to be reflashed). If not, contact the communication store for a replacement SIM card.
Does an unlocked bootloader (root access) affect the appearance of the error?
The presence of root access or an unlocked bootloader does not in itself cause an MMI error. However, installed mods, network tweaks, or specific kernels can change the behavior of the network stack, which leads to conflicts when sending service requests. Try temporarily disabling all network modifications.