This paper exhibits a novel technique to obtain a sensorless control of a permanent magnet synchronous motor post an open-circuit fault condition to achieve a maximum reliability of the whole drive system. The contribution of this work can be expressed in two things. The first contribution is the introducing of a 4-leg 27-level cascaded H-bridge inverter modulated through a 3D-space vector modulation technique to make the whole drive system fault tolerant. Besides that, an algorithm to track the saturation saliency position post an open-circuit fault is used to enhance the reliability of the whole system to meet the safety issues requires in some applications. This algorithm is based on measuring the transient current response of the motor line currents due to the (Insulated Gate Bipolar Transistors (IGBTs) switching actions. Then, according to the operating condition (healthy or post an open-circuit fault), the saliency position signals are constructed from the dynamic current responses. Simulation results are provided to demonstrate the effectiveness of the saliency-tracking technique under healthy and post an open-circuit fault condition. Moreover, the results will verify the maximum reliability for the whole drive system that is achieved in this work through a continuous operation of the drive system post an open-circuit fault condition and under sensorless speed control.