the light goes on when there is a problem with the airbag system. it is near impossible to fix or troubleshoot yourself and it is designed and kept that way so that only trained technician can fix it. the system has the power of a 9mm cartridge so if you do decide to delve into it, use extreme caution.
the srs light went off on my bimmer and i do not want to spend the money to send it in. i wanted to fix it myself, however documentation is limited to "contact a service technician". this includes the bentley manual.
i would have preferred that my bimmer not come with an airbag in the first place, and with the warning going off i know that it will never deploy. so the bulb for the light was removed
it could be anything from the charge, to the crash sensor, to a problem with the check system. . .