One is near the center of plenum rear and the other on the driver side. All the wires going to the grounding lugs are black. Those lugs need to be in good metal contact with plenum. Bad connections can destroy the PTU, make the car run poorly, etc. Grounding issues like this have been posted by others after a plenum pull.
No idea what's causing the speed sensor code but the grounding issue above may be related to it?