@ anthropoidape, try this it worked 4 me. props to cpritchford.

Open an X terminal and run this command

sudo gainroot

tail -f /proc/kmsg

CLOSE THE KEYBOARD..


Now, make a phone call on your phone (maybe to the answer phone service) or call your phone from another phone. Make sure the phone call is answered, not left ringing..


Now cover the left hand end of your phone with your hand (to cover the light sensor) or try putting against your head.. then pull it away/uncover.. repeat a few times.. then hang up the call


Now go back to the X Term..you should see lines like:


<6>[104495.511047] proximity (GPIO 89) is now closed
<6>[104668.252685] proximity (GPIO 89) is now open
<6>[104671.198028] proximity (GPIO 89) is now closed
<6>[104687.963623] proximity (GPIO 89) is now open


If you don't see that, the sensor is either inactive OR covered (screen protector) OR damaged..