try this app:
I'm new to the site as registered user since I have been always for information but I will start sharing my experience with you all.
The one I have is a LS980 sprint model unlocked and running a RayGlobe Flex 3.5 custom rom, I bought it that way and since I bought it knock on feature will not work (Knock off does).
So after checking the setting on about phone/hardware information it shows model D802 so whoever install/unlocked the phone changed the device name.
So I used the *802# code for the hidden menu and it showed up.
In the Hidden Menu (thats the title that shows) select HW Device Test / Touch Test / Touch Firmware Upgrade (It will show to wait 10 sec to check version)
I also did the option in the main Hidden Menu / Settings / Update Touch Firmware it will freeze for about 5 sec while doing the update and then you can go back to home screen on your device and try it.
That worked for me .
Here's some hidden menu secret codes. You might want to double check your model number in the phone settings.
3845#*802# (for International model)
3845#*801# (for T-Mobile)
3845#*800# (for AT&T)
5689#*980# – (for Sprint )
Dial: ##228378 + send (Verizon)
Other models, please use 3845#*YOUR-MODEL-NUMBER#
A second fix and more complicated one that I tried was to install custom rom CloudyG3 and it works just fine.
Hello to everyone,
after getting all this helpful info through this forum I've decided to contribute something myself.
I had the same issue after replacing my LG g2 screen. It worked fine before.
The problem in my case was the proximity sensor. It sits behind an oval window between the front facing camera and the light sensor. It has two small lenses, a bigger or the left and a smaller on the right.
If that sensor sits slightly wrong or the front rubber case is missing (I didn't noticed it the first time) or the required pressure from a small rubber behind (it is on the upper black secondary housing with the 7 screws) is not enough to hold it in a fixed certain place, it doesn't work correctly or at all.
When this happens the sensors detects near (meaning you have the device close to your face) and Knock unlocking is blocked. Also when you are making a call the screen goes off for the same reason, so it is easy to notice.
After I noticed and placed the front rubber case from the old screen, it was working, but slowly. It detected quickly the "near" position but it takes several seconds to re detect "far" position.
The final solution was reinforcing the small rectangular rubber which pushes the light sensor and the proximity sensor from behind, with two small pieces of sticker and the problem disappeared.
You can check that through the hidden menu (for my case 3845#*802#), HW Device test, ALC Proximity Test.
It should change rapidly from NEAR to FAR then waving your hand over the sensor.
If not, push firmly with one finger behind the sensor and see then if it is working