Check the contact on the side of the door, sometimes they get corroded and it won't send power to the lock.
You also may check to see if voltage is actually getting to the contact coming out of the coach, this will tell if the system is working and it is not the base module.
If you are getting power and you've cleaned the contacts it may be the actuator itself. This is inside the door and actually locks/unlocks the door.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi