Beginning in 1990, the Taurus and Sable (except 2.5L engine) were available with Anti-lock Braking System (ABS) as an option on vehicles with four wheel disc brakes. The system was standard on the Taurus SHO starting in 1990. The system prevents wheel lock-up by automatically modulating the brake pressure during emergency stopping. The system controls each front brake separately and the rear brakes as an axle set. During ABS operation, the driver will sense brake pedal pulsation, along with a slight up-and-down movement in the pedal height and a clicking sound; this is normal.