Sudden network loss is one of the most annoying problems faced by smartphone owners. You pick up the device, look at the upper right corner of the screen and instead of the usual signal “sticks” you see an icon of a crossed out SIM card or the words “No connection”. The situation becomes critical if you urgently need to make a call or access the Internet. Android does not see the SIM card for many reasons, ranging from a banal software failure to physical damage to the communication module.
Before taking the phone to a service center or panicking, it is worth carrying out an initial check diagnostics. Often the problem lies not in the device itself, but in the contact between the card and the reader, or in incorrect operation of the network settings. In this article, we will look in detail at why the “SIM card not detected” error occurs, how to fix the problem yourself, and in which cases professional repairs are required.
Physical reasons for lack of communication
The most common reason why a phone stops seeing a SIM card is due to physical contact. Over time, the metal contacts on the card itself or inside the smartphone tray can oxidize, become dirty, or become dislodged. Dust, pocket lint and moisture are the main enemies of a reliable connection. Even a microscopic layer of oxide can interrupt data transfer between the chip and the motherboard.
Often users independently cut SIM cards to the desired format (Mini, Micro, Nano) without using a special template or scissors. This leads to the chip being offset relative to the pad. As a result, when installed in the tray, the contacts simply do not match. Also, do not rule out mechanical damage to the card itself: cracks in the plastic or chips in the gold chip make it inoperable.
To exclude physical defects, you need to remove the tray and carefully inspect it. Pay attention to the spring contacts inside the slot: they should not be pressed in or bent. If the tray dangles or fits into the case too loosely, the geometry of the seat may be broken.
- 🔍 Inspect the golden SIM card chip for scratches, dark spots or signs of corrosion.
- 💨 Gently blow out the SIM card slot with compressed air to remove any accumulated dust.
- 🔄 Try installing the SIM card in another smartphone to check its functionality.
⚠️ Attention: Never use metal objects (needles, pins) to clean the contacts inside the smartphone slot. This can lead to a short circuit and irreversible damage to the power controller.
If the contacts of the SIM card are darkened, gently wipe them with a regular school eraser until a shine appears, and then remove any remaining rubber with a dry cloth.
Software failures and network settings
If the physical condition of the card and slots are fine, the problem may lie in the software. The operating system Android sometimes incorrectly processes radio module commands, especially after an unsuccessful firmware update or installation of third-party applications that interfere with the network. A failure can occur at the level of drivers responsible for interaction with the base station.
Often, users accidentally activate the "In-flight" mode or change the settings of the preferred network type. For example, if in your region the operator does not support the standard LTE at a certain frequency, and only this mode is forced in the settings, the phone will not be able to register on the network. It is also worth checking whether the SIM card is blocked via PIN codewhich was entered incorrectly several times in a row.
To eliminate software errors, it is recommended to reset the network settings. This action will return your connection settings to factory defaults without deleting your personal files, photos, or apps. The process takes only a few minutes, but often solves the problem of an “invisible” SIM card.
Go to menu Settings → System → Advanced settings → Reset Wi-Fi, mobile data and Bluetooth settings. After confirming the action, the device will reboot the network modules. If this does not help, try manually selecting a telecom operator in the menu Settings → SIM cards and mobile networks → Operators communications, disabling automatic selection.
Diagnostics through the engineering menu and flight mode
There is a quick way to “restart” the network search without completely rebooting the phone. Turning airplane mode on and off causes the radio to turn off completely and then re-initiate searching for available cell towers. This helps to reset the frozen registration process on the network.
A more advanced method is to use the engineering menu. In devices based on processors MediaTek and some models Samsung you can check the status of the SIM card through a special code. Enter in your phone ##4636## or *#0011#. In the menu that opens, select "Phone Information". Here you will see the status of the SIM card: if it is displayed as "Connected" or "Registered", the problem may be in the coverage, not in the device.
If in the engineering menu the status of the SIM card is displayed as "Absent" or "Unknown", this indicates that the system does not see the module at the hardware level. In this case, soft resets are unlikely to help, and the reason most likely lies in the hardware or a complete malfunction of the card itself.
*#06#Enter this code on the dial pad to check whether the device is displayed. If “Null” is displayed instead of the number or the field is empty, this is a serious sign of damage to the radio module or loss of communication with it. IMEI devices. If “Null” is displayed instead of a number or the field is empty, this is a serious sign of damage to the radio module or loss of communication with it.
What to do if IMEI is not displayed?
The absence of IMEI often indicates damage to the EFS partition in the phone’s memory or failure of the radio module. Restoration is only possible in a service center using programmers.
Problems with firmware and system updates
Failure to update the operating system is a common cause of loss of communication. If a power interruption or power surge occurred while installing new files, the partition responsible for the operation of the modem could be damaged. There are also cases when a new firmware version contains bugs that are incompatible with certain frequencies of telecom operators.
Sometimes the problem occurs after installing custom firmware or receiving root access. Users may accidentally delete system applications required for network operation or change radio configuration files. In such a situation, the phone may see the SIM card, but not register on the network, or constantly search for the network without results.
If you suspect that the problem is in the software, try performing a hard reset. Remember that this action will delete all data from the internal drive, so make a backup copy first. If this does not help, you will need to flash the device via a computer using official software, such as Odin for Samsung or SP Flash Tool for MediaTek.
| Type of failure | Symptoms | Solution method |
|---|---|---|
| Software glitch | The SIM card appears and then disappears | Reset network settings, reboot |
| Firmware error | The problem appeared after the update | Firmware rollback or flashing |
| Software conflict | The network disappears when launching certain applications | Starting in safe mode, deleting applications |
| Partition damage | Missing IMEI, status "Unknown" | Restoring the EFS partition in the service |
⚠️ Attention: Flashing the device yourself carries risks. If you are not sure of your actions, the wrong firmware version can turn your smartphone into a “brick.”
☑️ Actions if you suspect a firmware failure
Hardware faults and repairs
When all software methods have been exhausted and replacement The SIM card from the operator did not give any results, we are talking about a hardware failure. The most vulnerable element is the SIM reader (slot) itself. From frequent removal of the tray, the contacts inside it may become loose, stop springing, or come off the board. In dual-SIM smartphones, only one of the slots often fails, while the second continues to work properly.
A more serious problem is the radio module falling off. This is a chip on the motherboard that is responsible for receiving and transmitting signals. Due to overheating, falls or manufacturing defects, the soldering under the chip may be damaged. Symptoms of such a malfunction are not only the lack of a network, but also problems with the operation of Wi-Fi and Bluetooth, since these modules are often located nearby or combined into one chip.
It is also worth checking the power circuit of the SIM card. Small components on the board are responsible for this - resistors, capacitors and fuses. If one of them fails due to a power surge (for example, when connecting a low-quality charger), power will stop flowing to the slot and the phone will not see the card.
It is better to entrust the diagnosis of such faults to specialists. The technician will use a multimeter to check the presence of voltage at the contacts of the slot when the SIM card is inserted. If there is voltage, but there is no connection, the problem is in the reader itself. If there is no voltage, you need to look for an open circuit on the board.
If the phone was dropped into water, even if it turned on after that, oxidation of the SIM reader contacts may appear after a few weeks. The board needs to be cleaned with ultrasound.
Replacing the SIM card and contacting the operator
Sometimes the problem lies not in the phone, but in the SIM card itself. Plastic cards do not last forever: the chip can degrade over time, especially if the card is frequently moved between devices or is exposed to static electricity. Telecom operators recommend changing SIM cards every 3-5 years.
Contact your operator's service center with your passport. The procedure for replacing a card is usually free or costs a symbolic amount, and the phone number and tariff are retained. The new SIM card will have ideal contacts and support all modern security standards, which will eliminate problems with authorization on the network.
It is also worth checking with the operator whether technical work has been carried out on the towers in your area and whether your card is blocked due to suspicious activity or non-payment. Sometimes blocking on the operator's side simulates the absence of a SIM card in the device.
⚠️ Attention: When purchasing a new SIM card, make sure that it has the correct form factor (Nano-SIM) for your smartphone. Using adapters may result in the card getting stuck in the slot.
Save the packaging of the new SIM card (the plastic from which it was broken off). It contains a PUK code, which will be needed if you accidentally block the card by entering the wrong PIN code.
Frequent user questions (FAQ)
Why does the phone see one SIM card, but not the second in a dual-SIM device?
This indicates a malfunction of a specific slot (SIM reader) or problems with contacts in the second slot. Try swapping the cards. If the problem goes to the first slot, then the card itself is faulty. If the second slot continues to not see any card, the connector needs to be repaired.
Can a case interfere with the operation of a SIM card?
Yes, some thick or improperly designed cases can put pressure on the SIM card tray, preventing it from closing tightly. This causes the contacts to not touch properly. Remove the case and check the operation of the device without it.
What to do if the phone asks for a PUK code after rebooting?
This means that you entered the PIN code incorrectly three times. Find the PUK code on the plastic card included with the SIM card or in your operator’s personal account. Enter it to unlock the card and set a new PIN. Do not guess the code, because after 10 incorrect attempts the SIM card will be blocked forever.
Will resetting to factory settings help if the SIM reader is broken?
No. A factory reset only fixes software errors. If the problem is physical (broken connector, oxidized contacts, modem failure), a soft reset will not restore communication. In this case, hardware repair is necessary.