We have this problem with our almost 2 year old E91, according to our local dealer it is saying 1400 miles for the front but 17k for the rear!!!! They have said they will look at it under warranty but if the pads do need changed then that bit is chargeable so we are waiting til after Christmas! Bit that annoys me is it was serviced in September and they said both sets were fine and not worn, so why do the sensors now think they are?