2004 MDX awd not working

Hi: i have a 2004 MDX, the all wheel drive is not working at all, i replaced a fuse but still not working, help me please!!!.

I am not familiar with 2004 MDX, but on my son's 2005 Pilot a particular attention should be paid to the rear VTM-4 fluid.
What does your owner's manual say?

Sam