This many not be news to some, but I just figured it out now. I started up my 1999 Altima with the airbag out of the steering wheel, so of course the light was on. So I figured no big deal, I’ll just erase the code after reinstalling it. When I connect the scanner through the OBD2 connector and go to the AIRBAG section, it says no communication with the module. I try rebooting, jiggling the connector, charging the battery, etc. and nothing. Waste an hour doing that. Go to the generic OBD2 screen and no problem there, connects and reads the emissions related systems just fine. Turns out there is another connector by the fuse box as well. Check the box my scan tool came in and it has a dozen adapters including one for Nissan. Plug into that and now I can scan everything. I was under the assumption that all cars since 1996 when OBD2 became universal, would be able to have all the systems read from there, and only the 1995 and older models would need one of those adapters. Just a PSA if your tool isn't connecting. I assume this applies most for the first few years of OBD2 until the car makers enabled ALL systems to be scanned through the OBD2 connector.