Owners of mobile devices based on Android often face a sudden loss of network when, after a firmware update or an unsuccessful reset, the phone stops seeing the SIM card. In such cases, the settings display null or 000000000000000 instead of the unique device number. This problem lies in damage to the service memory section, which is called EFS.
EFS stands for Encrypted File System. This is a hidden section on the internal storage of the smartphone that stores critical data for the operation of the radio module. Without the information contained in EFS, your gadget turns into a media player without the ability to make calls and mobile data.
Understanding the structure of this section and the ability to work with it is a key skill for those who deal with custom firmware or restoring “bricked” devices. In this article, we will analyze in detail what exactly is stored in EFS, why it is damaged and what methods of restoring it exist.
Structure and purpose of the EFS partition
The EFS partition is part of the device’s system memory and contains unique identifiers assigned by the manufacturer at the factory. The most important element here is IMEI (International Mobile Equipment Identity). This is a 15-digit code by which cellular operators identify your device on the network.
In addition to the main identifier, the encrypted file system also stores other parameters necessary for the correct operation of the radio frequency module. The loss of this data leads to the fact that the modem cannot pass authorization in the operator’s network.
Here are the main data that it contains EFS:
- 📱 Unique number IMEI for each SIM card (in dual-SIM devices there are two of them).
- 📡 Calibration data antennas and frequency bands (Band).
- 🔐 MAC address of Wi-Fi and Bluetooth modules.
- 🌍 Regional network settings and country codes (CSC).
It is important to note that the structure EFS may differ depending on the device processor. On smartphones with chips Qualcomm Snapdragon this section often has specific markings that are different from devices with MediaTek or Exynos. That is why there are no universal recovery tools - methods are selected for a specific platform.
⚠️ Attention: The EFS partition is encrypted and tied to specific hardware. Copying this section from another phone (even the same model) will not help restore the network, since the cryptographic keys will not match.
Causes of damage and loss of EFS data
Why does such an important memory section fail? Most often, users themselves provoke the problem by trying to gain extended access rights to the system. The process of obtaining Rootrights or unlocking the bootloader (Bootloader) carries the risk of damaging service partition tables.
Another common reason is the installation of custom recovery (for example TWRP) or unofficial firmware. If the firmware image was built with errors or is not intended for your specific board revision, the installation script may accidentally overwrite the area EFS.
Physical damage to the device can also lead to data loss. Shocks, moisture or power surges during charging can damage the memory cells where encrypted information is stored. In rare cases, a failure occurs after an unsuccessful over-the-air (OTA) update if the process was interrupted.
Technical details of the failure
If the EFS is damaged, the modem goes into emergency mode. In the system logs (logcat) this is often reflected by errors like “RIL – Request failed” or a complete lack of response from the radio module. Diagnostics through the engineering menu (*#06#) in this case will show zeros instead of numbers.
Is it worth trying to recover the data yourself? If you have a fresh backup, definitely yes. If there is no backup copy, the process becomes more complicated and requires the use of specialized PC software.
Diagnostics of the problem: how to understand that EFS is damaged
The first and most obvious sign of damage EFS is the absence of a network. Even if the indicator shows the signal level, calls do not go through and the Internet does not work. However, there are other symptoms that will help you accurately diagnose the problem.
Check your device settings. Go to menu Settings → About phone → Status (the path may differ depending on the shell). If in the “IMEI” field you see dashes, zeros or an inscription Unknownthen the partition is damaged.
You can also use the engineering code. Open the Phone application and enter the command *#06#. A pop-up window with codes should appear on the screen. If the window does not appear or the data is incorrect, this is a sure sign of a failure.
Diagnostics via ADB are available for advanced users. Connect your phone to the computer and run the command in the terminal:
adb shell service call iphonesubinfo 1If you receive an empty result or an error in response, it means that the radio module cannot read data from EFS.
Before starting any manipulations with memory sections, be sure to make a complete backup of user data to your computer or to the cloud. Restoring EFS is a risky procedure that can lead to complete loss of data.
Methods for restoring EFS and IMEI
Restoring the radio module depends on the availability of a backup copy. This is the easiest and safest way. If you backed up the partition in advance using recovery or special utilities, the process will take several minutes.
If there is no backup, the situation becomes more complicated. You will need to find a “donor” EFS file that is suitable specifically for your model and board revision, or use service apps from the manufacturer (for example, Odin for Samsung or QPST for Qualcomm), which can overwrite the calibration data.
Consider the checklist of actions if you have a backup:
☑️ Restoring from backup
When using PC utilities, the process looks different. You need to install the modem drivers, put the phone into download mode (Download Mode or EDL) and download the corresponding image file. An error at any stage can lead to the device being no longer detected by the computer.
| Recovery method | Required tools | Difficulty | Risk of data loss |
|---|---|---|---|
| Recovery from TWRP | Recovery, backup file | Low | Minimal |
| QPST utility (Qualcomm) | PC, drivers, cable | High | Medium |
| Service center | Professional boxing | Absent | Low |
| Recording via ADB | PC, root access, terminal | Medium | High |
⚠️ Attention: Using foreign EFS files from the Internet is highly not recommended. Incorrect calibration data can lead to incorrect operation of GPS, Wi-Fi, or even overheating of the radio module due to incorrect signal strength.
The most reliable recovery method is to have your own backup copy, made immediately after purchasing the device or before any modifications to the system.
How to create an EFS backup (Backup)
To protect yourself from future problems, you need to regularly create backup copies of critical sections. This is especially true before updating the firmware, obtaining root access or unlocking the bootloader.
The most popular method is using custom recovery TWRP. In the menu Backup you need to select a section EFS (sometimes called Modem or Persist) and swipe to confirm the creation of the image. The file will be saved to the internal memory or SD card.
For devices with root access, there are special applications, such as EFS Professional or IMEI Changer (backup function). They allow you to save data to the cloud or send it by email with one click.
You can also create a copy manually via ADB if USB debugging is enabled. The command to create the image is as follows:
adb pull /dev/block/mmcblk0p13 efs.imgPlease note that the partition number (mmcblk0p13) may differ on different devices. You can clarify the exact location of the section using the command ls -l /dev/block/by-name/.
Where to store the backup?
Never store the only copy of EFS only on the internal memory of the phone. If there is a serious failure, you may lose access to the entire device. It is recommended to duplicate the file on your computer, cloud drive (Google Drive, Yandex.Disk) and external SD card.
Prevention and precautions
The best treatment is prevention. To avoid loss IMEI, you should follow a number of rules when operating and modifying your smartphone. Do not install firmware designed for other models, even if they seem compatible.
Always check the integrity of the downloaded firmware files using checksums (MD5 or SHA1). An archive damaged during loading may contain errors that will appear only when written to memory.
If you plan to sell the device, do not forget to reset the settings correctly, but do not touch the service partitions manually. The buyer will be grateful for a working phone, and you will save yourself from possible claims.
Remember that interfering with the operation EFS may violate the manufacturer's warranty. If the device is under warranty, it is better to solve any communication problems through an authorized service center.
⚠️ Attention: Menu interfaces, section names and commands may differ depending on the version of Android and the device manufacturer. Always check the documentation for your specific model before executing commands.
Regularly backing up the EFS partition only takes a couple of minutes, but can save hours of time and stress when restoring the device in the future.
Frequently asked questions (FAQ)
Is it possible to change the IMEI legal?
In most countries, changing the IMEI is illegal, as this number is used to block stolen devices. This is technically possible via writing to EFS, but we do not recommend or support such actions.
Will a factory reset help restore EFS?
No. Factory Reset clears only the user partition /data and the cache. The partition EFS is in a protected area and is not affected by a normal reset. If the data there is damaged, it will remain damaged.
Why does the network disappear after updating the firmware?
Most often this happens due to the incompatibility of the modem part (Radio/Modem) of the new firmware with your device. It is also possible that the installation script accidentally erased the partition EFS. The solution is to reflash the stock modem or restore from a backup.
What is the Persist partition and is it related to EFS?
The partition Persist stores sensors and calibration data other than the radio module (for example, screen calibration, accelerometer). It is often paired with EFS, and its damage can also cause unstable operation of the phone, although the network may remain working.
Is it possible to restore IMEI without a computer?
Only if you have a backup file on the memory card and have custom recovery (TWRP) installed. In other cases, when recording at a low level is required, it is almost impossible to do without connecting to a PC and special software.