When your favorite Xiaomi or Redmi smartphone suddenly stops seeing your SIM card, it always takes you by surprise. The screen can show a “No Service” message or a crossed-out SIM icon, depriving you of connectivity and mobile Internet. This is a common problem that can be caused by both a software failure in the MIUI system and physical damage to contacts. In most cases, the communication module can be restored without contacting the service center, if you act consistently.
Before you panic and carry the device to the wizard, you need to rule out trivial causes such as contact contamination or a temporary failure of the radio module. Often, it is enough to follow a simple algorithm of actions to make the network reappear. In this article, we will examine in detail all possible causes, from improper trimming of the SIM card to complex hardware malfunctions, and offer step-by-step instructions for their elimination.
Understanding the nature of the problem is half the success of solving it. If the device does not detect the SIM card after the reboot, this may indicate a software conflict or physical wear of the slot. We will look at diagnostic methods that will help you determine exactly where the failure occurred, and return the gadget to full life.
Basic diagnostics and reboot of modules
The first step when a problem is detected should always be to restart the device, not just a cliché, but a necessary process to reset temporary errors in the operating system. As you work, errors accumulate in memory that can block the radio part from working. If conventional shutdown and turn on did not help, try a deeper method of restarting the radio module.
To do this, go to the settings menu and find the section responsible for SIM cards and mobile networks, where you can force a particular SIM card to be disabled and re-activated. This soft restart often helps the system to read back the data from the chip without fully restarting the phone. If the network icon appeared for even a second and disappeared, the problem is likely to be in the software.
It's also worth checking if the flight mode is activated. Sometimes the system sticks in this state, and even after the flight mode is turned off, the communication module does not start. Turn on the flight mode for 10-15 seconds, and then turn it off. This action forcibly initiates a search for available operator base stations.
If simple manipulations fail, go to physical testing. Take out the SIM card tray and examine it carefully. Make sure the tray is inserted on the correct side before the click. Slim fit is a common cause of loss of contact. Also check if the tray itself is deformed, as even curvature can disrupt the connection of contacts.
Checking the physical condition of the SIM card and tray
Physical damage is one of the most common reasons why Xiaomi doesn't see the SIM card.The contacts on the card itself may have oxidized, contaminated or micro-scratches.Take a soft dry cloth or eraser and gently wipe the golden contacts.Don't use wet wipes or aggressive chemicals, as moisture inside the phone can short circuit.
Notice the size of the SIM card. If you cut your own card from large format to Nano-SIM, the edges could be uneven or chipped. It can get stuck in the tray or not reach the contacts. Modern smartphones use the Nano-SIM standard, and any deviations from the size are unacceptable. Better replace the card in the operator's cabin, it is free and takes a couple of minutes.
⚠️ Warning: Never insert a SIM card in the tray with a microSD card unless the tray design provides for it.
Check the integrity of the tray itself. Some Redmi and Poco models have rather fragile trays. If the tray plastic is cracked or the contacts are bent, the SIM card will not be powered. Visually compare the position of the contacts on the tray to the image of a serviceable device on the Internet. If you notice that one of the contacts falls or, conversely, sticks out above the others, you will need to change the tray.
Try installing your SIM card on another phone, and if it's not there, the problem is guaranteed in the card itself, and it needs to be changed by the operator, and if the other phone is working, then the problem is in your Xiaomi smartphone, and you need to look for a malfunction in the slot or software part.
Set up network and APN settings
Sometimes the SIM card is physically healthy, but the phone cannot register with the network due to incorrect settings of the APN access points. This is especially true when changing the operator or after resetting. To check, go to Settings → SIM cards and mobile networks → Select SIM card → Access Points (APN).
If the list is empty or the settings look suspicious, click the reset button (usually at the bottom of the screen or in the three-point menu). The system will automatically download the correct settings for your region and operator. After the reset, be sure to restart the device.
☑️ Checking network settings
It is also important to check the network mode. In the mobile network menu, make sure that LTE or 5G/LTE/3G/2G mode is selected. If 2G only or 3G mode is selected, the phone may not see the network if these standards are already disabled in your area by the operator.
In rare cases, manual network registration helps. Go to the SIM card settings, select Operators, and turn off automatic selection. Wait for the phone to scan the air. If you see your operator on the list, select it manually. If the list is empty or registration is constantly interrupted, this is a sign of a more serious problem with the antenna module.
Software failures and reset network settings
Complex software conflicts in the MIUI shell can block modem operation, often after a failed system upgrade or installation of applications that have access to telephony. If rebooting doesn't help, try resetting the network settings, which will return Wi-Fi, Bluetooth and mobile settings to factory values, but will not delete your personal files or contacts.
To perform the reset, go to Settings → Connection and Sharing → Reset Wi-Fi, mobile networks and Bluetooth. Confirm the action. After that, the phone will reboot. You will have to re-enter the passwords from Wi-Fi networks, but this often solves the problem of “losing” the SIM card.
| Action. | Impact on data | Effectiveness in the case of a SIM problem |
|---|---|---|
| Flight mode | No. | Low (temporary solution) |
| Reboot. | No. | Medium |
| Resetting network settings | Save photos/contacts | Tall. |
| Full reset (Wipe) | Deletes everything. | Maximum (if not iron) |
If you don't have a network reset, you can try a more radical method, a factory reset. Careful: make sure you back up all the important data before you do that, because the phone will be cleaned completely. If the problem persists after a clean reset without installing third-party apps, the probability of hardware failure is as high as 90%.
How to make a backup copy before resetting?
Hardware malfunctions and communication module
When software methods are exhausted, we have to talk about hardware. In Xiaomi smartphones, a common problem is the failure of the SIM card slot itself. Contacts inside the phone can become oxidized by moisture or simply lose their elasticity over time, in which case only replacing the slot in the service center helps.
Another major cause is a collapse of the antenna module or a plume, and if the phone fell, the connector connecting the motherboard to the antenna could have moved away, and the symptoms of this damage are not only the lack of a SIM card, but also a weak signal or its complete absence even at the full scale on the screen, and diagnostics require disassembly of the device and multimeter check.
In rare cases, the problem lies with the processor or modem itself, especially if the device has been overheated or impacted, and repairing such components is complex and requires professional equipment. If the diagnostics reveal a motherboard malfunction, it is often more cost-effective to replace the device than to repair it.
⚠️ Warning: Do not try to disassemble the phone yourself if you do not have experience. Damage to plumes or leakproof housing can permanently disable the device and deprive you of warranty.
Impact of MIUI Updates and Firmware Reflash
Updates to the MIUI operating system sometimes contain bugs that disrupt the radio module. Users often notice that after the arrival of the “heavy” update, the phone stops seeing the SIM card, in which case waiting for the next patch or, conversely, rolling back on the previous stable version of the firmware helps.
If you are using a global firmware version on a Chinese device or custom build, conflicts may arise due to incompatibility of frequencies or drivers. In such cases, it is recommended to return to stock factory firmware through a computer using the Mi Flash Tool utility.
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Use Clear All mode when flashing through the Mi Flash Tool to completely remove old system files that may conflict with the new version of the software.
Check the version of the basic modem firmware. Sometimes you can see the modem status in the developer settings or through the engineering menu. If the modem version doesn't match the system version, the communication won't work. Updating to the latest available version often solves this problem automatically.
Specificity of two-symbol models
Owners of dual-SIM models often face a situation where only one of the slots is not working.This may be due to the fact that the second slot is hybrid and shares resources with the memory card. Check in the settings if there is a mode where the second slot only works in 2G mode, which modern networks no longer support.
If the SIM card from slot 1 stopped working in slot 2, and the SIM card from slot 2 earned in slot 1, then the first slot is faulty. If the SIM card does not work in any slot, the problem is in it or in the general power controller.
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If the SIM card is not detected in either of the two slots, and in other phones works - a malfunction of the motherboard or smartphone power controller is likely.
Some older Xiaomi models may not support certain carrier-specific 4G/LTE frequencies in the second slot.Make sure your phone and SIM card are technically compatible.