I was driving my 03 400 sportsman and all of a sudden the 4x4 kicked in on one side and pulled it hard to the right,the switch was turned off.What would cause this?

 

change the hub fluid. take aparty the hub and clean it and make sure power is getting down to it. you have only one hub engaging is why it pulled hard to the right. a few ideas to try. imo

 

Usually the armature plate is magnetized on the pulling side from wear or low on fluid. change the fluid first and see if helps. If not I'd replace both sides as the other plate will probably go also,usually fairly quickly! I've done a couple this past week.

 

the plates are brand new,i will check the fluid level.What gets me is the 4x4 switch was not turned on.

 

could be a broken retainer spring