Double check the connection on your FAD unit on the passenger side of the front axle, from the perspective of left hand drive vehicles. If this unit is disconnected or the plug is loose it throws SERV 4WD in any drive mode.
It's trivial to crawl under and look at as a first step that might save you a long headache with the dealer, ruling out something quick and obvious.
The fad looks like this - this is a shot I pulled from Google but they all look the same really - just check that the electrical connector shown is fully secured.