Well I didn't want to say Jim was wrong, but it sure looks like the diagnsotic connector to me.
The device you want is similar looking except it has numbers and or letters instead of holes about the periphery. The diagnostic connector is just the end of a bunch of wires.
The piece you would be looking for (not saying it exists) would be basically black about as big around as one of our quarters and have resistors inside (you can't see this though). By unplugging it and turning the outer piece the resistance changes to the controller bringing up various timing maps.
Bosch Master, ASE Master, L1
33 years MB technician