I would check your fluid level as mine was low and the 4wd light would come on for no reason after id been driving a while. When it happened i would turn the car off then back on and it would turn off, but when i toped up the fluid it seems to have fixed it tho it has done it once since and i just figured it must have been maybe a air bubble in the line. Not sure if this helps If you find the prob and its something else can you let me know in case iv just been lucky!!
Cheers