A method for monitoring an electric power circuit configured to transfer a power signal to a torque module that is electrically isolated from a chassis ground includes injecting a common voltage component into a common mode voltage of electrical phases during operation and monitoring a negative-ground voltage and a positive-negative voltage of the electric power circuit. An AC line resistance is determined based upon the negative-ground voltage and the positive-negative voltage. Faults in electrical isolation between the electric power circuit and a chassis ground are detected based upon the AC line resistance.