What is ABS sensor? 

ABS (Anti-lock Braking System) is an enhanced braking system which is commonly found in newer automobiles. The anti-lock braking system uses an ABS o wheel sensor to monitor the wheel speed and send this information to the ABS computer. The ABS computer uses its information to prevent brakes from locking during an emergency stop. ABS sensor is a type of tachometer measures otational speed of the wheel and passes it to Engine Control Module (ECM). 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.