The power locks to my car will only work to lock the car but not to unlock it. Somehow over the course of time, the transmitters have lost the ability to open the car when the 'open' button is pressed. Is there a frequency re-adjustment that can be performed so that the car can read the frequency correctly? Does anyone know where the door locking module/receiver is located in this model car? Any thoughts would be appreciated. I have already serviced the transmitters (cleaned the contacts) with partial success that does not last very long.