'01 4runner rear speed sensor out

I was told by e mechanic quite a while ago that one of my rear wheel speed sensors is bad. My ABS, and VSC lights are on. I cannot remember if they said it was the left or right rear speed sensor. Is there a way I can check it myself to see which one is bad? If I were to guess it would be a 50/50 shot, but with my luck I would pick the wrong one.

Thanks for your help!!!
Jason