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IMEI is a unique identification number programmed onto your device and you can check the unique IMEI of your device by dialing *#06# or written on sticker under the battery. It is required in order to be correctly identified on a mobile network.
Without IMEI, you cannot make calls, send SMS or use mobile data.

EFS is a partition on the internal memory of your device which contain important data including the IMEI.
If the data in this partition gets corrupt, you will lose your IMEI

Requirements :
1. Samsung galaxy S4 device
2. "Android Terminal Emulator" app (Link below)

EFS Backing up Steps :
1. Open "Android Terminal Emulator" and type
Then enter
It will ask for root permission
Then enter
B.  For galaxy S4 all LTE and US variant Type :
Then enter

C.  For galaxy S3 all LTE and US variant Type :

dd if=/dev/block/mmcblk0p11 of=/sdcard/efs.img

dd if=/dev/block/mmcblk0p12 of=/sdcard/mod1.bin

dd if=/dev/block/mmcblk0p13 of=/sdcard/mod2.bin

Then enter

3. Backup the created files on your phones internal storage to your PC or the cloud.

EFS Restoring Steps :
1. Send the files (Step 3) to the internal storage of your device
2. Open "Android Terminal Emulator" and type :
Then enter
It will ask for root permission
3.A. For galaxy S4 GT-I9500 Type :
Then enter
B. For galaxy S4 all LTE and US variant Type :
Then enter

C. For galaxy S3 all LTE and US variant Type :

dd if=/sdcard/efs.img of=/dev/block/mmcblk0p11

dd if=/sdcard/mod1.bin of=/dev/block/mmcblk0p12

dd if=/sdcard/mod2.bin of=/dev/block/mmcblk0p13 

Then enter

4. Restart your device
Done !
Notes :
~ It wont delete your data
~ Make sure you choose the correct cmd in restoring process
~ This method will work only on ROOTED devices
~ Backing up EFS partition is highly recommended for users who use the custom Roms
~ Use it at your own risk
~ This method wont repair your device if you dont have a backup of the EFS partition, but you can to try this How to Fix "Not Registered on Network"/Wrong IMEI for Galaxy S3/S4/Note2
~ Every device has unique partition, so you cant use this if you have backup file from another device

Downloads :
Android Terminal Emulator App HERE