No expert here, but what I've learned:
If you uncouple and recouple an air bag system connector without disconnecting the battery, it will set a code (I cycled a connector under the seat before learning this).
OBD2 is federally mandated for emissions and basically covers the status of the engine and emissions systems. This is what the basic scanners read. ABS, airbag, etc. are proprietary and need a special ($$$) scanner. If you get a scanner, I'd make sure it covers your specific vehicle.
I had an airbag problem that turned out to be the clockspring, apparently the weakest link in a typical airbag system. I replaced the clockspring but still had the airbag light. Not wanting to spend the time and money ($100) to have a dealer reset it, I went to a local body shop that had done work for us earlier. The owner had a mechanic reset the codes and told me "no charge". I slipped the mechanic a $20 and everyone was happy.