There are numerous things that can cause issues with the 4wd on these machines. Speedo not working, voltage at the diff, too little fluid in diff, too much fluid in diff, dirty fluid, wrong fluid, warped armature plate, or broken sprague cage. In that order. Start by checking the speedo, if that works then move down to the diff. to see if you have voltage. If you have voltage, then drain the fluid and ensure you put the proper amount of the Polaris Demand Drive fluid. If that doesn't work then take it apart and look at the sprague cage. If it is cracked or broken, replace it. Also check the armature plate while your in there. It only takes it being warped .005" for it to cause engagement issues.
2009 SPORTSMAN 800 H.O.
RUBBER DOWN CUSTOMS 2" LIFT
EPI HD SPRINGS
29.5 S/W OUTLAWS ON ITP SS312
GORILLA REAR PROP SHAFT
SUPER ATV BILLET CAGE IN FRONT DIFF.
SUPER ATV ARMATURE
WELDED LOW GEAR IN TRANSMISSION
QUAD SHOP CUSTOMS CLUTCHING
TRIANGLE ATV STEALTH SNORKLE
TRIANGLE ATV REAR RACK PLATE WITH AMMO CANS
RIDE N'REST BACKREST W/FROSTY BEVERAGE HOLDER
K&N AIR FILTER
PURE POLARIS FRONT AND REAR BUMPERS
POLARIS FRONT AND REAR RACK EXTENDERS
POLARIS 3500 WINCH
POLARIS OEM BELT