My key fob intermittently works for locking and unlocking my doors the horn nevealready replace the battery in the key fob the trunk button works all the time

open up the key fob again. On the side of the circuit board opposite the battery, there are contact patches where the black carbon pads in the silicone cover makes contact when you press the buttons. Using rubbing alcohol, gently clean both the contact patches on the board and the carbon contacts themselves. If there is any deterioration on the board itself, it will require professional repair. At that point, Look on Ebay for a good used fob.