Had an ongoing problem with my ABS light being on. The car had this when I bought it, I got the car anyway because it was a good deal and my last car an 850 always had this problem and it never caused me a problem. Anyway...I finally tracked down the issue. The axle on most cars is secured to the hub with a large nut abd cotter pin. On the S80 a washer and a bolt is used. Sometime before I bought it the drivers side lost the bolt. I would occasionally hear a washboard vibratuon in the front end...this was the cv joint coming inwards a bit out of the hub and getting out of balance. This caused the bumps on the cv joint on the hub end from engaging the ABS sensor. This made the ABS system think it was bad. I had a hard time dissasembling as the splines in the hub were rusted...but I got it back together replaced the bolt with sone locktite and my ABS works perfectly.