Don't know about the parts manual, but there could be two other causes for that part being there. First either wayward piece falling into the engine area during the build and just being missed after assembly, then somehow rattling itself loose. Or second, road debris getting flung up into your car, then dislodging later. I had a piece of truck tire that got lodged into my underbody of a prior vehicle and was rubbing as slow speeds. The force that it came off the road to make it stick into the plastic underbody panel must have been pretty great. I didn't notice it when it happened, only after the rubbing.