A control system may include a polarity determination module, a torque variation module, and a torque sensor diagnostic module. The polarity determination module determines a first polarity of a torque signal that indicates a transmission torque. The torque sensor diagnostic module diagnoses an error of a torque sensor when an detected polarity of the torque signal is opposite from the first polarity. A control system may include a torque variation module and a torque sensor diagnostic module. The torque variation module determines a maximum torque variation during a predetermined diagnostic period based on the torque signal. The torque sensor diagnostic module diagnoses an error of a torque sensor when the maximum torque variation is outside of a torque variation range. The torque variation range is defined by a minimum torque variation threshold and a maximum torque variation threshold.