I know this is an old post but I figured I'd follow up on what I've found.
This car when I bought it had the issue of water getting into the cabin because the weather stripping at the bottom of the windshield had fallen off. Needless to say the airbag SDM under the passenger seat took on some water damage and I believe it'* toast.
Heres a pic:
Now I just need to know what other GM cars have this exact unit, I have a pick n pull very close to me - it can't be only in Grand Prixs I would think...