Install Android 5.1 Lollipop on Galaxy S3 I9300 with Unofficial CyanogenMod 12.1 custom Firmware

Samsung Galaxy S3 GT-I9300 came with 1 GB of RAM, Super AMOLED capacitive touchscreen and Quad-core 1.4 GHz Cortex-A9 Processor, but Samsung stopped Android support for this smartphone due to hardware limitations and there is no chance of Samsung official Android 5.1 update, but it doesn’t mean that this device cannot taste the sweetness of Lollipop. Thanks to custom ROMs, the Android 5.1 update is now available for the Galaxy S3 GT-I9300.

If you have Galaxy S3 I9300 and want to get the Android Lollipop firmware then here is a good news for you that CyanogenMod 12.1 ROM (Alpha) has been released for the Galaxy S3 GT-I9300 (International Variant) by Scorpionea (Senior XDA Member), this ROM is based on the latest Android 5.1 Lollipop which seems to be much quicker and smoother. But as this AOSP ROM is in beta stage, so you might expect some bugs, apart from a few non-functional features and some settings are missing (from Android 5.0.2 Lollipop) as well as the navbar icons are too big.

If you have decided to get CM12.1 custom ROM featuring Android 5.1 Lollipop then we’ve a step by step guide to update your Galaxy S3 to this latest custom firmware. You’ll need to have a custom recovery like TWRP in order to install the firmware and Gapps .zip files on your phone.

Android 5.1 Lollipop CM12.1 ROM Details:

  • GT-I9300
  • ROM: 12.1 arter97 experimental
  • Baseband: i9300XXUGNA8
  • Kernel: 3.0.31 CM

Bugs Fixed:

  • Messenger crash (fix with installation of textra -> play store)
  • Camera does not work (fix with installation of Kamera Zoom FX -> play store)

Open Bugs/Problems:

  • Encryption does not work (try the fix mentioned here, which does not work, but does not get stuck in broken recovery)


This guide containing the download links for CyanogenMod 12.1 Alpha ROM, Google Apps, TWRP open recovery and instructions are working with the International Galaxy S3 (GT-I9300) only. Do not try to install this firmware on any other device or incorrect variant. You should verify the model number of your device first.

Warning: will not be held responsible for any kind of damage or mishap occurred to your Galaxy S3 during or after the updating process of unofficial CyanogenMod 12.1 based on 5.1 Lollipop. Proceed at your own risk.

Before Getting Started:

  • Create a proper backup of all your existing data and settings on the phone before proceeding to the installation guide using a recommended custom recovery.
  • Enable USB Debugging Mode on the Galaxy S3 by navigating to Settings > About Phone.
  • Verify that you’ve properly installed the Galaxy S3 USB Drivers on the PC.
  • The Galaxy S3 should be rooted with the latest version of custom recovery like CWM or TWRP installed.
  • The bootloader of your S3 must be unlocked.
  • Make sure that the battery level of the Galaxy S3 is at least above 80% before going ahead.

Required Files:

Steps to Update Galaxy S3 GT-I9300 to Android 5.1 Lollipop with Unofficial CyanogenMod 12.1 custom ROM:

Follow the given instructions to install CyanogenMod 12.1 ROM featuring Android 5.1 manually on Galaxy S3:

Step No 1:- First of all download the Android 5.1 Lollipop CyangoenMod 12.1  ROM, Google Apps and TWRP recovery to a folder on the desktop of your PC.

Step No 2:- Transfer the downloaded ROM, Gapps and TWRP files to the root folder of your SD Card.

Step No 3:- Next, turn OFF your Galaxy S3 to boot into Recovery Mode. Turn the device ON while pressing and holding Power + Home + Volume Up keys at the same time till the TWRP logo appears.

Step No 4:- While your Galaxy S3 is in recovery mode. Navigate to the recovery menu and select Backup.

Step No 5:- Swipe on the Swipe to Back Up option on the bottom of the screen on your phone.

Step No 6:- Perform Wipe of Data, Dalvik cache, Cache and System after the process is completed.

Step No 7:- Go back to the main menu of Recovery and select Install, then navigate to the root folder of your SD Card where you have saved the ROM, select the ROM and click on Swipe to Confirm Flash option. This process may take some time, so wait for the process to be finished successfully.

Step No 8:- Once done, perform Wipe Dalvik Cache again.

Step No 9:- Go to the recovery menu and select RebootSystem to reboot the phone.

Step No 10:- Now, install the Google Apps package on your Galaxy S3 by repeating the above steps.

Step No 11:- Navigate to the TWRP main recovery menu once the Gapps package is installed and select Reboot > System.

Done! You’ve successfully installed CM12.1 ROM featuring Android 5.1 manually on Galaxy S3 GT-I9300.

Let us know in the comments area below if you have any question or trouble while updating your S3 to this CM12.1 custom firmware.


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