OnePlus released OxygenOS 3.5.9 update for OnePlus 2 with VoLTE fix and other improvements. Users will get the OTA update in the comming days. The OxygenOS 3.5.9 update is mainly for fixing VoLTE issue and network drop issue that affected some OnePlus 2 devices. It seems that the update is region specific and intended only for those affected with VoLTE issue and network drop issue. You can check for OxygenOS 3.5.9 OTA update by going to Settings > About > System update. Alternatively, you can download and install the full OTA update manually.
The OxygenOS 3.5.9 update mainly fixes VoLTE issue in OnePlus 2 . However, the update may include general bug fixes, performance enhancements and stability improvements. The incremental OTA (over the air) update will get all affected OnePlus 2 and will reach on all devices in the coming days.
OxygenOS 3.5.9 is based on Android Marshmallow. Unfortunately, OnePlus will not update OnePlus 2 to Android Nougat. However, users can install custom ROM like LineageOS to get latest Android Nougat or the upcoming Android O on the device.
If you are facing VoLTE and network drop issue, and prefer manual installation, you can download the full OxygenOS 3.5.9 firmware (1.2GB) and flash via stock recovery. Also, the file will not overwrite your settings and data.
1. Download OxygenOS 3.5.9 full OTA update zip file (1.2GB) from here and save it on your phone’s internal memory.
2. Boot your OnePlus 2 into stock recovery by pressing and holding Volume Up and Power buttons together.
3. In recovery, choose language and then select Install from Local.
4. Select for the update zip file that you saved in step 1 and tap on Install.
5. Once done reboot your phone and enjoy.