The Haynes manual is crapparific for wiring diagrams. You could download the OEM manual, say from:
http://www.hondahookup.com/manuals/ or
http://www.honda.co.uk/owner/workshopmanuals.html
The Hall sensor is like the original post said.
Basic info:
http://autorepair.about.com/library/.../bldef-291.htm
Look at the position of yours when you take the rotor out you should see this & the plate in line with it. If your metal plate is warped or broken, that could be it.
I don't know if this would cause the error code, but it is a no-start: bad main relay (
http://autorepair.about.com/cs/troub.../aa010301a.htm). Maybe someone else could comment on the likelihood of this?