P0845 is a 2/4 hydrulic pressure code, The problems could be a solenoid pack, TRS ( transmission range switch), wiring or TCM ( transmission control module). You could replace the solenoid pack and hope it fixs the problem. I think the question you were asking was where is the sensor for circuit B, That would be part of the TRS. Which is connected the the valve body. and the switch would be part of the solenoid pack.