Failure diagnosis device for vehicle body acceleration sensor and anti-lock brake system

The present invention reduces a control processing load of a vehicle-use antilock brake system attributed to a trouble diagnosis of a sensor which is mounted on a vehicle and has an output thereof changed corresponding to a traveling state of the vehicle during traveling of the vehicle, particularly a vehicle body acceleration sensor which detects the vehicle body acceleration of the vehicle. From a point of time that a vehicle speed becomes a preset speed ³ (4m/s) or more (timing indicated by symbol T1), the storing and the updating of a maximum value Gmax and a minimum value Gmin of an output value of the vehicle body acceleration sensor 1 are started and it is determined whether the difference between the maximum value Gmax and the minimum value Gmin, that is, a fluctuation width of the output value of the vehicle body acceleration sensor 1 becomes a preset fluctuation width ´ or more or not. Then, at a point of time that the fluctuation width of the output value of the vehicle body acceleration sensor 1 becomes the preset fluctuation width ´ or more, an output fixing trouble detection stop flag of the vehicle body acceleration sensor 1 is changed over from OFF to ON and hence, the detection of the output fixing trouble of the vehicle body acceleration sensor 1 is not performed (timing indicated by symbol T2).