Why the second line on the Xiaomi phone does not work: reasons and solutions

When you buy a new smartphone or replace it SIM-The second line on Xiaomi’s phone suddenly stops responding, causing a natural irritation: instead of the expected two active numbers, only one is displayed in the status bar, or the second slot is marked as “Not connected”. The problem can lie in the banal physical incompatibility of the SIM plastic, and in the software conflict of the operating system. MIUI or hyperos.

Today’s Xiaomi devices, whether budget Redmi or flagship Xiaomi, are technically fully ready for two networks to work simultaneously. However, reality often makes its own adjustments: the operator changes access parameters, the user accidentally knocks down priority settings, or the card itself was improperly cropped. In this article, we will examine all possible causes and provide a step-by-step algorithm of actions.

First of all, you need to eliminate the basic errors that are often overlooked in the initial diagnosis. Physical contact and correct installation of the card are the foundation of stable operation. If the device has recently been subjected to a fall or moisture, the problem may be hardware, but in 90% of cases the matter is solved by software methods or replacing the plastic of the SIM card from the operator.

Physical causes and verification SIM-map

The first thing to do if the second SIM card stops working is to check the integrity and compatibility of the card itself. SIM-Mini or Micro cards inserted through an adapter may not provide stable contact in modern trays, especially for hybrid slot models where the card's pressing mechanism is more sensitive to the thickness of the design.

It's also worth looking carefully at the contacts on the gold chip. Oxidation, greasy spots or micro scratches can cause the phone to simply "not see" the card inserted. Try gently wipe the chip with a dry soft cloth. If you have the opportunity, install the problem one. SIM-The first slot is the card, and the working slot is the second slot, so you can see if the problem is in the particular port or the map itself.

⚠️ Note: Never use a homemade adapter for SIM-They are often thicker, which can lead to a tray getting stuck or damage to the contacts inside the smartphone.

It is important to consider the age of the SIM card itself. Telecom operators are gradually moving to 4G/5G standards, and older cards issued more than 5-7 years ago may not work correctly in new networks, especially if LTE preferred use mode is enabled.

Network settings and priority SIM-map

If the card is physically OK, the next step is to check the software settings. MIUI The control of the lines is handled by a separate module, which may sometimes not work properly after the system update. → SIM-maps and mobile networks and make sure the switch opposite the second card is activated.

A common cause of problems is a conflict of network modes. SIM-Priority of the card 5G/LTE, And the second card is in the unsustained area, and the system can automatically turn off the second module to save energy or to avoid overheating. 3G/2G and check if the signal is coming.

• 📱 Go to the settings. SIM-Check if the card is “unplugged».
• 🌐 Make sure the correct operator is selected for the second line in manual mode if the automatic search does not produce results.
• 🔋 Check the charge saving settings: aggressive modes can block background activity of the second SIM.

The Flight Mode feature deserves special attention. Sometimes the communication module freezes, and simply turning on / off the air mode does not help. In such cases, a deeper reset of network settings, which we will discuss in the next section, helps. Also check whether the Background Data Limitation function is activated for the second SIM, which may create an illusion of inoperability.

Resetting network settings and reconnecting

When simple manipulations don't work, you need to reset your network settings, and this action will return your connection settings to factory values by removing the accumulated configuration errors, and it's important to understand that this won't delete your personal files, photos, or contacts, but it will forget your saved Wi-Fi passwords and Bluetooth device settings.

To perform the procedure, go on the Settings path → Connection and sharing → Reset Wi-Fi, mobile networks and Bluetooth, and once confirmed, the phone will restart, and as you boot it will re-initialize the modem and try to register both. SIM-Maps in the operator's network with clean parameters.

Resetting Path: Settings → Connection and Sharing → Resetting Wi-Fi, Mobile Networks and Bluetooth → Resetting

After the reboot, don't be in a hurry to check the Internet right away. 2-3 If the second line is up, but the Internet is not working, the access points may have gone down. APN. They can be configured manually or request automatic settings from the operator through USSD-team.

Conflicts with VoLTE and 5G

Modern communication standards such as VoLTE (Voice over LTE) and VoWiFi allow you to make calls over the Internet protocol without switching to 3G. However, on some Xiaomi models, the implementation of these functions can be unstable, especially if the carrier has not officially certified the device.

Try disabling VoLTE for both cards.The path to setup is usually in the Settings menu. → SIM-maps and mobile networks → (Select a SIM) → If the second line is activated after disabling this option, then the problem lies in the incompatibility of your operator’s standards and the firmware of the phone.

Also worth mentioning is Smart 5G mode, which automatically switches networks to save charge. Sometimes this algorithm is too aggressive and completely disables the second SIM module if it thinks it is not in use at the moment.

⚠️ Note: Global versions of firmware (Global) ROM) The VoLTE hidden settings menu may not be available, in which case activation is only possible through the engineering menu or special applications, which requires caution.

Software updates and regional features

Software bugs are another common cause of the Dual SIM’s instability. Xiaomi regularly releases security updates and patches for modems that fix communication errors. If your version of MIUI or HyperOS was released a few months ago, there are high chances that it has known problems.

Check for updates in Settings → About Phone, but there is a caveat: sometimes the problem appears after the update, in which case forum users often advise to change the region of the device. Switching to Settings Additional → Region to India or Singapore can unlock hidden frequency settings and improve the operation of communication modules.

• 🔄 Check for system updates in manual mode.
• 🌍 Change device region to activate additional communication profiles.
• 📡 Make sure the basic modem firmware version is up to date.

Changing the region does not affect the interface language and application performance, but can change the range of frequencies available and the behavior of the system when working with two SIM cards, this is especially true for devices imported from China (CN Version), which are used with European or Russian carriers.

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Before changing the region, back up important data, although this action rarely leads to loss of information, reinsurance will never be superfluous.

Hardware malfunctions and diagnostics

If none of the software methods worked, there's a high probability of hardware failure. SIM-A card, a plume of an antenna, or a power controller on the motherboard malfunction, which often occurs after falls, bumps, or moisture, even if the phone looks whole.

For initial diagnosis, you can run the Xiaomi engineering menu. Type the code ##64663## on the keyboard of the caller. SIM-maps (usually item) SIM The system will check the card's presence, signal strength and the ability to register on the network. If the test shows an error, the problem is almost guaranteed by the hardware.

In case of confirmation of hardware breakdown, self-repair is not recommended, as it requires soldering and special equipment. It is better to contact an authorized service center. Replacement of the tray is an inexpensive procedure, but if the controller on the board is damaged, repair may not be economically feasible for older models.

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If the engineering test shows an error SIM-cards on a serviceable plastic, the problem lies in the hardware part of the smartphone, not in the settings.

Frequently Asked Questions (FAQ)