My drivers airbag light has been on for about 3 years, I had an mot recently and this got switched off using the sd2 as suggested above. However the light was back on again before I picked the car back up following the MOT. I was told its probably a switch in the glove compartment, there is also an airbag ecu but that is unlikely. I have heard its a simple fix to replace the switch in the glove box, if that doesn't resolve it I might get a new airbag and then finally the ecu if all else fails. I've seen all the parts on ebay recently. Sorry I can not be more specific about the parts, I haven't really bothered lkooking into this, yet.