Thank you all for your responses and help.
I've replaced the entire Reversing assembly, which includes the PS109 sensor.
When I peform the manual sensor test, both on this mfp and another that is fully functional, "K" doesn't change from 0 to 1, like "H" does, but the screen flashes whenever I press on the PS109. This leads me to belieive that the sensor is functioning properly.
I have run the component tests on all parts and they are functioning properly.
I have checked for blockages/paper in the top cover area and cannot see any, nor does shoving cardstock in there indicate any blockage.
