Would it be possible to test a failure in these items? Or would I have to open up the unit and see if it's bad? And if so Is it possible to buy these items at a local auto parts store? Or something I would have to search the internet to find?

Hi, my name is Steven & I'm new to the forum. I own a 2002 S60 AWD, & love the vehicle..but I've had a feeling during my time of ownership & winter in NY that the AWD isn't working/engaging. All the fuses are in good condition, & I just recently had it on a lift with the tires off th...