Generally has to do with connections and not the expensive airbag itself.
Look here.
https://sites.google.com/site/mikefocke2/airbagwarninglighttsb but also note that there are some very specific diagnostic codes that are available to someone who has access to the right diagnostic hardware and software. Something you can buy that would help diagnose the engine codes and the airbag codes is called Durametric and installs on a Windows laptop.