Located on the transmission case, within the rear differential assembly or inside the ABS, the vehicle speed sensor reads the wheel rotation speed on a vehicle while driving. The sensor also helps the car maintain stability while driving by telling the computer when to release pressure to a wheel while using the ABS. A type of tachometer, the part consists of a toothed ring and pickup. Speed sensors within the differential use a trigger wheel mounted in conjunction with the ring gear to accomplish the same tasks as those performed by the transmission-mounted version. The speed sensor reads the rotational speed of the reluctor wheel located within the transmission.