Originally Posted by Irongrave
I pulled the screen out today. Its layers of plastic fabric mesh with a charcoal/carbon media impeded between them. My best guess is that its there to remove some of the airborne pollutants thus helping it lower the emissions out of the tail pipe. I will report back with any codes if there are any.
From your description, the material seems like that of an air purifier filter. So it probably serves the same purpose too.