I believe the arm is the sensor.
I did find this article in the Support Pages that may help you find a resolution to the jam issue.
No paper jam anywhere to be found, but I'm getting "Jam in the Document Feeder" 005-908.
I assume some sensor somewhere gave up its ghost? Does this error code indicate which specific sensor is claiming there is paper?
Found https://forum.support.xerox.com/t5/Copying-Faxing-Scanning/Scanner-Jam/m-p/227480 and the photo -- is it that sensor? I assume that's an optical one, so perhaps the LED has gone out? (Is there a schematic somewhere?)
Or what other sensor might it be?
P.S. If Apple can now publish repair guides, what about Xerox?