2005 Dodge Caravan Automatic Door Locks

The locks on this vehicle automatically lock once you reach 10 mph, approximately. They are not doing that now. The door lock switch inside the vehicle that automatically locks all doors when pushed no longer locks the doors either. The remote that locks the doors when you push the button does not lock the doors either. The only way is to manually lock each door. What could the problem be and how is it repaired?