Steering angle issue c1231 - How to clear hard fault

I don't have a copy of the Gen 4 repair manual to easily refer to. I'd have to find it here

Toyota Service Information and Where To Find It | PriusChat

where you would find it also. The section on the C1231 code would be where you would learn both exactly what the code is telling you (not some abridged memory jog you might find for it elsewhere) and what to do about it.

If I remember right, steering angle sensors in earlier generations (2 and 3) were kind of self-zeroing. The ECU didn't care much what absolute signal the sensor was sending, but as soon as you drove for a bit, it would look for a moment when the yaw sensor read zero and the left/right wheel speeds were equal, and whatever the steering angle sensor said at that moment would be saved as steering angle "zero". So that approach required an accurate zero setting for the yaw sensor (and there's a Techstream procedure for that), but it avoided needing any separate special procedure for the steering angle sensor.

I remember being puzzled in a Gen 2 because the steering angle shown in the Data List could be some goofy value, every time the car powered up, until it had been driven some and that auto-zero had taken place.

I don't know whether Gen 4 details are at all the same.