[iangaryprice]

There is a speed sensor on each wheel, the are mainly used by the ABS system. Also now used for Tyre pressure warning (basic system that does not have sensors in the tyres) and also used for the vehicle speed and traction control.
My previous car was a Ford Mondeo the sensors fail frequently on them, often after wheel bearings or brake discs had been replaced, sometimes they only needa clean, but once you g=have removed them might as well replace them for the cost.
Not heard of them failing on VW's. Metal particles from drake discs can cause them to misread, some mechanics also claim Copper grease can as well. The connnectors can be a problem as well due to water ingress.