I've posted this link a couple of times but I think it should be in a separate thread which I hope Rob Lay will add to the F355 sticky. The document at the following link provide some of the best insight as to how OBD II works that I have found. It is circa 1998 so very relevant to the F355 OBD II system. I encourage everyone to download and read it. http://www.lbcc.edu/attc/documents/OBD2.pdf
Ya, that is worth saving for my less savvy friend who do not understand what the check engine light means... Great simple explanations with sufficient technical detail to make it clear how the system "thinks" about engine management. The F355 engine management system is fairly decent.
John emailed this to me before posting here. Thank you, John. I'm not thru it yet (slow reader lol) but what I've read so far is very interesting and informative.