PS4 Controller: Arrow keys do not respond except the very lowest, what can I do?
If the warranty has already expired, you can, if you dare unscrew the controller and see if you can find the problem. If you still have warranty on the controller, I advise you not to open the controller, otherwise the warranty expires. You can then send it to Sony and they'll fix it for you.
If the former is the case, then be careful, the controller gets hard the first time and you have to be careful, otherwise you'll break more than heal.