Abstract: To address typical faults caused by speed signal processing in traction drive systems, this paper investigates the working principle of speed sensors and the zero-speed judgment logic. It is found that the duration of zero-speed judgment directly affects motor control performance. Theoretical analysis and simulation verification are conducted based on field cases, including a pit trap overcurrent fault, excessive traction force during gradient starting, and an overcurrent fault caused by a single-axle speed sensor failure under bogie control mode. The mechanism by which speed distortion due to zero-speed judgment affects indirect stator-quantity control (ISC) is revealed. An optimization method that appropriately shortens the zero-speed judgment time while maintaining low-speed resolution is proposed. Field tests confirm the effectiveness of the proposed solution.