A vehicle ground fault detection system for detecting a ground fault includes a fault detection circuit having a resistance element. The resistance element has one side connected to a supply voltage. An electrical switching circuit is connected to the resistance element for selectably coupling the other side of the resistance element to a secondary ground. The fault detection circuit further includes a fault detection sense line connected to a junction between the other side of the resistance element and the electrical switching circuit. A controller selectably couples the resistance element to the secondary ground. The controller is coupled to the fault detection sense line to receive a voltage signal for detecting the ground fault prior to a start-up of the AC step-up power transformation. The controller determines a ground fault based on a comparison responsive to the voltage signal and a predetermined comparative value.