A ground fault detector and detection method for a vehicle that can
determine the cause of the occurrence of a ground fault after detecting
the presence of the ground fault. The output terminal of a high-voltage
battery is connected to one side of a coupling capacitor. In operation, a
pulse signal is applied to a measurement point on the other side of the
coupling capacitor, and the voltage generated at that point is detected.
Whether the high-voltage battery or the electrical equipment units are
grounded is determined. To determine the cause of the ground fault, the
oscillation frequency of the square-wave pulse signal is changed and
applied to the measurement point. From the change in voltage amplitude
detected, it is determined whether the cause of the ground fault is a
resistive or a capacitive ground fault, according to the change in the
impedance of the battery or the units.