Brakes

If the ABS system is at fault, they are expensive to replace. You could have a warped rotor(s) on one or more of the wheels. This usually happens if the tires are replaced and the lug nuts are tightened way past specifications. The rotor cannot expand properly as they heat up, causing them to warp. Same can happen if the brakes get real hot and you run through deep standing water. One way to check is to jack up the wheel and turn it by hand. If it seems to bind at one location or another, they are warped.