The existing fault diagnosis schemes for inter-turn and inter-phase short circuits in permanent magnet traction motors can be roughly summarized into two approaches. One is to add sensors, which increases the system complexity and cost. The other is that the observation method is too complicated, and its robustness and universality need to be improved. Aiming at the disadvantages of these two technical approaches, this paper takes the change of the transfer impedance between the positive and negative sequence components inside the Permanent Magnet Synchronous Motor (PMSM) as the breakthrough point, analyzes the law of the characteristic impedance changing with the motor state and operating conditions, and proposes a diagnostic scheme that is simple to calculate and has universality. Under the operating conditions, the double dq transformation method is used to extract the positive and negative sequence components, and the variation of the transfer impedance is calculated in real time and compared with the safety threshold. When it exceeds the threshold, an early warning of the inter-turn short circuit fault can be issued. Under the shutdown conditions, a high-frequency signal is injected to make the motor generate symmetrical three-phase currents when the rotor is stationary. Then, the characteristic impedance is calculated by means of the double dq transformation method. Once it exceeds the safety threshold, it can be diagnosed as an inter-phase short circuit fault. Finally, a short circuit fault model of the permanent magnet synchronous motor is built based on PLECS, and the proposed scheme is verified. This method is simple to implement, has low computational complexity, high sensitivity, and a wide application range.