An ABS (Anti-lock Braking System) is an enhanced braking system which is commonly found in newer automobiles. An anti-lock brake sensor or ABS sensor is a type of tachometer that measures the rotational speed of a wheel and passes it to the car's Engine Control Module (ECM). The ABS sensor is also called the wheel speed sensor or ABS brake sensor. Since all the wheels do not turn at the same speed, the ABS sensors report the speeds of all the four wheels to the ECM, based on which the ECM determines if the wheels are locking up. The application of the ABS brake is quicker than manual brakes. Due to this, when the ABS is engaged, it emits a grinding noise in some automobiles.

The ABS sensor is the main sensor that keeps the braking power of a car in check. The sensor transmits the rotational information to the ECM to signal that one of the tires is locked up, in which case, the computer will lower the amount of braking force applied to the wheel in question. As the braking force decreases, the wheel can now turn and regain its grip. Many modern vehicles also have ABS sensors which interact with the electronic traction control systems and stability control systems to ensure vehicle safety.