A power steering assembly includes a steering unit and a motor. A controller includes a processor and tangible, non-transitory memory on which is recorded instructions for executing a method of self-diagnosis for the assembly. If a plurality of enabling conditions is met, the steering unit is caused to rotate through a plurality of angles from an original position, via a command to the motor. The steering unit is caused to rotate first in a forward direction up to a predefined maximum angle, second in a reverse direction up to a negative of the predefined maximum angle and third in the forward direction back to the original position. The controller is configured to obtain motor torque data characterizing torque of the motor at the plurality of angles. The assembly is controlled based at least partially on the motor torque data and predetermined baseline data.