4WD Auto

[Maxim]

Hi, just acquired a 2010 3.5l Alphard last weekend. Seriously impressed so far.

 

I've searched but can't find the answer to this question - apologies in advance if it is already posted somewhere obvious...

 

What does the "4WD Auto" button do?

e.g.  is the car normally in 2WD and with the button activated it automatically decides when to drive the rear wheels,  or is the car normally in 4WD and with the button activated it goes into 2WD with auto 4WD detection, or something else altogether?

 

I looked under the car, it has a driveshaft and diff, so I know it has a mechanical 4WD system.