No problems with Trooper since new.

Currently drives perfectly with no odd noises, vibrations or concerns.

CURRENT PROBLEM: 4x4 will not engage! When I press the shift-on-fly dash switch, the 4x4 dash light blinks normally and there is a small "click" (solenoid?) within the dash, as normal, but the front wheels do not engage whatsoever.

4x4 worked perfectly last winter, but mysteriously stopped working at first snowfall this year.

What should I check?