Figure.1 shows a two-axle vehicle equipped with ABS, it’s a 4S/4M system. (4 wheel-speed sensors and 4 modulator valves) The main principle and components of ABS are as follows: wheel-speed sensors (3) monitor each wheel’s speed; ABS modulator valves (4) modulate the pressure of brake cylinder (5) ECU (1) control valve according to the sensor signals. ECU receives the inductive signals produced by tooth wheel (2) and sends the signals to valve. The valve modulates the braking pressure of brake cylinder according to the signals sent by ECU. ABS warning lamp is used to remind driver whether ABS works normally