I'm trying to remember because its been awhile since looking in my 06 TSX engine bay (handed down to my son in 2014). I think that is the cover for the air intake. It drops below the battery into the resonator and back up into the bottom of the airbox. I think I remembered it wasn't secured and pulled up very easily. It was never out of place and it shouldn't give you the type of error you had.
Dad - 19 MDX Sport Hybrid Adv Fathom Blue Pearl w/ Graystone
Mom - 18 RLX Sport Hybrid Brilliant Red Metallic w/ Ebony
06 TSX w/ Navi (Totaled Oct/19), 08 RDX Tech (Daughter), 11 MDX Adv/Ent