DTC C121A: Abnormality in steering wheel sensor calibration: Operation
WARNING: This page is about a different car, the 2015 Mitsubishi Lancer. However, it is still accessible from the selected car via links, so may be relevant.
Steering wheel sensor stores the neutral position learned by scan tool. When the neutral position has not been stored in the steering wheel sensor yet, the steering wheel sensor outputs the signal indicating that it does not have neutral position.