A method for monitoring a PSM machine having three phases including detecting whether one or more current sensors disposed on a phase of the machine has malfunctioned. If a malfunction is detected, a voltage indicator is calculated from a voltage amplitude and a voltage phase of an input voltage of the machine in a d, q-coordinate system by two different calculations. The first calculation includes calculating the input voltage based on a phase current, target currents, and an electrical angle of the machine. The second calculation includes calculating the input voltage based on target values of a reference voltage amplitude and a reference voltage phase. The method also includes determining the voltage amplitude and the voltage phase of the input voltage of the machine and comparing the values of the respective voltage amplitudes and voltage phases from the input voltage in the first and second calculations.