How did you check the pump?
Sometimes what happens is the shaft breaks inside the pump and you can't see it. If you don't have a gauge simply loosen a pressure line and start the car. If fluid blows out the pump is good. If it just drips out because the line is loose then the pump needs replaced.
Yes, in the back of the pump.
If stuck it would still work fine when driving just not when turning in a parking lot.
Make sure getting power to it and that it is not open.
Instructions on how to replace:
Steering Wheel Position Sensor Replacement Removal Procedure