OBD II is attrocious. That's why people avoid the 96 and newer cars like the plague. I thought part of OBD II was pre and post cat O2 sensors in addition to the 82 plus sensors that are part of OBD II. I don't think the Z is an exception. I could be wrong since I have limited Z experience, but this was true for my M3 and a friend's Supra Turbo.