This is just an FYI for anyone else who may try this. I figured it would be convenient to have this Y splitter on my OBDII port since I have the SCT handheld hooked up to my car so often for tweaking with the SCT Pro Racer Package. After hooking up the splitter, everything looked OK until I went to write a tune. The SCT XCal 3 then gave an error message and would fail to write. Sorry I forgot to make a note of the actual error code it produced. Simply removing the splitter and hooking the XCal 3 directly to the OBDII port fixed the issue.
I also did not have anything else hooked up to the Y splitter.