If you mess up a step while rooting your Galaxy S9 or S9 Plus or maybe you just want to go back to stock firmware, you can easily do it using ODIN and stock firmware files. Btw, process is identical for all Galaxy smartphones except the firmware file is different.
Before beginning, download all the files you will need:
Download ODIN & Drivers – Link
Download Galaxy S9 & S9 Plus firmware – Link
Step 1. Power off your Galaxy S9 or S9 Plus, then hold down Volume Down, Bixby, and Power buttons for about 5 seconds until you see a warning scree.
Step 2. Hit the Volume Up key to enter ODIN download mode and connect a USB cable from your Galaxy S9/S9 Plus to your Windows computer. FYI, you will need a Windows computer do unroot your Galaxy S9 or S9 Plus as ODIN is a software only supported by Windows.
Step 3. Unzip the ODIN zip file you downloaded earlier and run the ODIN EXE program(the file ending in EXE).
You should see a blue-highlighted box with random COM number if you previously installed the Samsung USB drivers. If you don’t see that box at this point, simply run the Samsung USB EXE driver installation program you downloaded earlier. Then unplug/re-plug your USB cable to your S9/S9 Plus and you will see it. If you still don’t see it, try another USB port and do not use a USB hub as sometimes they interfere with it.
Next, unzip the stock firmware zip file you downloaded earlier.
Next, choose “BL” and select the firmware file starting with “BL”.
Next, choose “CP” and select the firmware file starting with “CP”.
Next, choose “AP” and select the firmware file starting with “AP”.
Now, in most cases, you do not need to select “CSC” as it only changes your CSC. I don’t personally flash it ever but if you don’t want to lose data, choose “CSC” and select the firmware file starting with “Home CSC”. If you are installing on top of a stock firmware or unrooting stock firmware, this will allow you to keep data. But MAKE A BACKUP of EVERYTHING before preceding as you can still mess up(beginner’s luck) and it is always good idea to backup anything important.(You can use Samsung Smart Switch app to backup all your apps and important data, which comes with your phone, do a search in the app search bar for “smart switch”.)
NOTE: If you do NOT FLASH CSC, ODIN WILL ERASE EVERYTHING ON YOUR PHONE except your microSD card storage!!!
When ready, hit “Start” button and the stock firmware will begin flashing, it should take around 5-10 minutes and reboot by itself.
Step 4. Once done, your Galaxy S9/S9 Plus will reboot by itself and boot to a fresh Welcome screen OR simply boot if you used “Home CSC”.
Note: DO NOT use “Home_CSC” if you are coming from a custom ROM(if you are on a custom ROM and unrooting) as the data will not be compatible and you may end up in a nasty bootloop(you can also fix this by doing a factory reset in stock recovery, which will erase EVERYTHING on your phone or you can also re-install TWRP recovery and do a factory reset there, which will allow you to keep your personal files on the internal storage and only reset your apps and app data.)
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