2006 Dodge Van Coolant Fan keeps running

We drove through a big water puddle and the van continued to run fine. However, when we got home and shut it off, the coolant fan kept running. The radiator was fine, coolant level good, temp gauge perfect, but the fan kept going. We disconnected battery cable and waited, Re-connected, and fan came back on (this was several hours later, and van had not been re-started). Is there a switch somewhere? Is this an expensive repair>
Thanks
Joanne