ABS

Anti-lock braking system. Abs prevents the wheels from locking so that the vehicle slows down faster and so that the driver can control the vehicle while braking hard. ABS uses wheel speed sensors to calculate how fast the wheels are moving and whether they are locked up. If a wheel does lock up the abs system reduces the pressure going to it until it moves the same speed as the other wheels then the pressure is supplied to it again.

The system can be checked with a scanning tool to see if the wheel speed sensors, the motor and the valves  are all working correctly. If there is a problem with one of the sensors a multimeter or an oscilloscope can be used to check the sensor and the wires connecting it to the ABS controller.