I had a 2003 Town and Country with the battery going mysteriously going dead. One day I came home with our other car and as I walked by the van I heard the electric cooling fab start up on a cold engine.
It turned out to be the cooling fan control module. Your Pacifica uses the same module. On the van, the module was mounted on top of the steel front bumper under the rubber bumper cover just to the drivers side of the radiator.