Usally when your light comes on the sensor is a contact switch which i think most recommed to change it not very expensive. Go to this site
www.bavauto.com they have tons of stuff for cars like ours I have bought from them there are a good company. sensor cables from this company are about 15 to 20 dollars. If you replaced brake pads before light came on cable sensor does not have to be change. Thats what i was told but if you have so many miles on the car and pad replacement is necesary I would do it anyway since cable is not that expensive