Hm...ah didn't quite understand the english there....actually if it is the possibility of the case impeding the sensor...ya ....take it out of the case...try it out...if it still doesn't work...and there is no method to change the setting in "settings" then ya...you need a diagnostic tool.

If it is the case impeding...locate exactly where on it that the sensor lies underneath ....mark that spot....take the phone out....grab an x-acto knife and cut that small section out of the case...voila! it should now work with the case on.
Sadly though...no duct tape was used.
As Red Green the duct tape expert says..."If the women don't find you handsome, they should at least find you handy."