Traction motors, as essential electromechanical energy conversion devices, play a vital role in heavy-haul locomotives. The transition of railway transportation to higher power, higher speeds, and heavier axle loads intensifies dynamic interactions within locomotive traction systems. This shift results in more frequent motor failures, significantly affecting the performance of the traction transmission system. Previous studies have relied on dq-axis motor models, making it challenging to adjust motor parameters to accurately simulate various motor fault types and severities. Consequently, the impact of motor faults on locomotive traction transmission systems has not been thoroughly explored. To address this gap, this paper aims to develop a locomotive dynamics model incorporating the traction transmission system. The model replaces the dq-based motor model with an improved multiple coupled circuit model considering the interaction between the stator and rotor-bearing system. This enables a more precise simulation of the electromechanical dynamic interactions of traction motors within the traction transmission system under varying levels of fault severity. The electromechanical response characteristics and influence laws of the traction transmission system under conditions of broken rotor bars and stator inter-turn short-circuit faults are investigated. The results indicate that broken rotor bars cause low-frequency fluctuations in stator current, pulsating torque, and significant variations in wheel–rail longitudinal forces. An increase in broken rotor bars further amplifies fluctuations in the electromechanical response. Stator inter-turn short circuits result in three-phase current unbalances and elevated amplitudes at specific frequencies. The short-circuit turn ratio exerts a more significant influence on current unbalance than the short-circuit resistance. Under motor faults, the electromechanical coupling effects become weakened. This research provides a theoretical foundation for fault diagnosis in locomotive traction motors.