I replaced my VSS because my speedo was only displaying half my actual speed and tranny was acting up as a result, and VSS code was issued. I only done it from below because I had seen a mechanic at the dealership do it like that on a Taurus while I was retrieving my van after the first recall. At that moment it had not occurred to me that the Taurus had a different transmission and a larger engine bay with less clutter underneath, and even a different platform than a '00 Winnie. That only registered once I was in the process of removing the cats. But when I start something, no matter how ill-conceived my approach turns out to be, I stubbornly stick to it. Took me 4 hours... and I still had the code!!!
That's when I noticed the ABS light was on... again. It had been on for a while but I didn't think it was a big deal. I was dead wrong. Being already covered in grease and soot I decided I may as well replace that little wheel sensor, at least the day would not be a total disaster. I proceeded a and lo and behold, no more VSS code, speedometer back to normal, transmission shifting normally. That's when I decided to investigate what exactly was it that those ABS sensors were meant for other than braking, and found that they are properly called wheel speed sensors. From there it doesn't take a genius to figure that a lot of stuff depends on them working properly. Since then I keep spare ones in the vehicle.
But since then I am also a bit confused: what is the VSS for anyway?
BTW I believe starting in '01 wheel speed sensors were moved to the rear wheels, which would make sense for accurate data even in icy conditions when front wheels may skid-spin.