TROUBLE SHOOTING APPARATUS FOR WHEEL SPEED SENSOR SIGNAL SYSTEM

PURPOSE:To enable detection of troubles of disconnection and short-circuiting of a signal line by a method wherein a stabilization voltage and a resistance are used in the signal line to give the line a specified voltage and an input voltage into an A/D conversion input port is monitored with respect to the specified voltage. CONSTITUTION:When a signal line 60 is normal, a line 71 is given a signal voltage which varies centered on a voltage as obtained by dividing a power source voltage Vcc by resistances R4 and R5 and the voltage is introduced into an A/D conversion input port of a microcomputer 51 as reference voltage through a line 73. When a line 60 is disconnected, a capacitor C1 is charged by the current through the resistances R4 and R2 and a voltage Vcc is led out to the line 73, so that an input voltage of an A/D port turns to the voltage Vcc. When the line 60 is short-circuited to a ground potential, the capacitor C1 discharges by the current to the line 60 and input voltages of the line 73 and the A/D port turn to the ground potential. Thus, troubles of disconnection or short-circuiting of the line 60 can be detected by monitoring the input voltage to the A/D port.