I've just changed one the other day due to there being a fault, I was surprised how corroded it was and ended up snapping off. So had to strip it down and the fault was the sensor ring as it had just corroded so had to put a new bearing on as well . Apparently a lot of places always do the bearing,sensor ring, when doing the rear abs fault as it's more likely to be that, which they can tell normally on a fault scan if they have the right equipment .