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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.


AndroidBlog 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.


  • 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:

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.

2:- Transfer the downloaded ROM, Gapps and TWRP files to the root folder of your SD Card.

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.

4:- While your Galaxy S3 is in recovery mode. Navigate to the recovery menu and select Backup.

5:- Swipe on the Swipe to Back Up option on the bottom of the screen on your phone.

6:- Perform Wipe of Data, Dalvik cache, Cache and System after the process is completed.

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.

8:- Once done, perform Wipe Dalvik Cache again.

9:- Go to the recovery menu and select RebootSystem to reboot the phone.

10:- Now, install the Google Apps package on your Galaxy S3 by repeating the above steps.

10:- 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.


Aamir Jamal

An Android Geek and audiophile who love to read and write reviews/tutorials about gadgets and new tech stuff. He has written 1007 guides and other posts.

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  1. Great Post, Followed your steps on S3 i9300, Now my phone is having CyanogenMod 12.1, thanks,
    Also i want to know how to root my device , initially it shows “root access” in developer option after flashing, but after i downloaded and installed supersu , i cant find that option in developer section , Plz help me to root my device

  2. Hi. I have downloaded Lollipop 5.0.2 few weeks ago, and i wish to update it to 5.1 now.
    should i follow the same steps above? Thanks

  3. Hi I have followed the above steps and after step 6 while installing the rom it says failed. Please help

  4. Hi, I was able to successfully install and get the phone working. There are 2 issues

    1. Not able to send the sms text via messenger (but I can receive). I couldn’t find Voice+ to disable as suggested in other forums. Please help to fix this issue

    2. Sent contact via SMS is not working. I get message “Unfortunately Contacts has stopped”.

    Please help me in fixing these issues. 1st issue is really critical.


  5. With GoSMS and was able to send/receive text messages. But still text sending is not working with the stock “Messaging” application. Any help to make stock “Messaging” to work?


  6. Had upgraded from CM11 to CM12.1. Installation / Upgrading happened flawlessly. However after the update, the mobile data is not working.
    1) Camera 360 Ultimate = OK
    2) all email apps working fine
    3) all messenger apps working fine.
    4) SMS thru Textra working fine.

    Have had issues only with mobile data connectivity.
    Would appreciate your help.

    Thanks & Best Regards

  7. i can’t find wifi hotspot thetering in this rom, can you tell me where is it??and sometimes camera malfunction… how to fix it?? thanqs…

  8. I installed this version, and it does not work I google play store,, google services appears locked and I had to uninstall the app. Keyboard lock also appears occasionally, the front camera has little resolution and has 16 × 9 High resolution. Is there any patch or new version with these error solution? thanks

  9. Thanks, Love you guys 🙂 I tried this with CWM and it didn’t work, works majestically with TWRP Doe!

  10. i followed all the above steps when i rebooted an error message keeps bobing up saying unfortunately google play services has stopped don’t know what to do ???

  11. Hi guys, I’ve followed all above steps, but when I reboot my device and I try to open google play, appear an error message like this: “Unfortunately google play services has stopped”…

    I don’t know what is happening.. Please help me to solve this problem.

  12. Hi guys I have solve my gt-i9300 not registered network problem If I flash this ROM this problem will appear again or not?

  13. I also get the message Unfortunately google play services has stopped.
    I tried re-install Google Apps and now i can see Gmail and Hungout crashing one after another on a loop.
    Any ideas ?

  14. I have recently installed a custom firmware but most apps don’t run like the latest
    lates opera and the and some of the apps that come with the firmware e.g the browser and the audio fx

  15. how to fix this problem. i cant drag icon from menu at home page. and “unfortunetely, trebuchet has stopped”

  16. Hello,
    I did follow the steps and installed in my S3. update was successful.
    But now when I am installing a new app and trying to access it Mobile is getting stuck all the time so I am clearing the cache and again rebooting it all the time.
    Any permanent FIX please let me know

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