Abstract: In order to detect the minor fault of the current sensor in the permanent magnet synchronous motor (PMSM) drive system of new energy vehicle timely and accurately, a minor fault diagnosis method based on adaptive sliding mode observer is proposed in this paper. First, the hybrid logic dynamic model of the drive system with minor fault of current sensor is constructed, and then the fault reconstruction of minor fault of current sensor is carried out by using state augmentation and nonsingular coordinate transformation. In addition, an adaptive sliding mode observer with fast convergence and high-frequency chattering suppression is designed to accurately estimate the reconstructed state of the system. Finally, the residual between the actual value and the observed value of the system reconstruction state is used as the detection variable, and the norm is used to design the adaptive threshold. The method proposed in this paper can not only diagnose minor fault and obvious fault, but also detect the whole process from minor fault to fault and even failure, with high accuracy and strong robustness. The experimental results verify the accuracy and robustness of the proposed diagnosis method.