I was driving up a mnt. on our farm. My EV was in 4 wheel drive-low range. I came to a low area where there was a good bit of mud. My back tires started spinning but my front tires never would engage/ pull. I backed up several times to try again and I finally made it through but any idea why my 4 wheel drive didn't work properly. This is a new 2016 that I've only used twice. the 4 wheel drive worked fine last weekend when I used it.