I had the same problem... but I was just getting onto a highway..!!! BOOM,, drivers side airbag blew.
There is a seam where the floor panel meets the firewall, and I believe there is a ridge on the engine compartment side. My driveway is sloped and I think moisture and salt sat in this ridge and after I pulled the carpet and the sticky foil from the interior side, I found the metal had rotted out,, about 2 feet long and 1/2 high. I had a body shop repair this. I still have some other smaller leaking but can't find the source. This hole caused water to enter and that shorted out the airbag module under the carpet, under the passenger seat. I bought a drivers air bag and module from the wrecker for $250. I installed the airbag but not the module, and I removed the old module. I contacted GM and a rep meet me at the local GM dealer and looked things over to verify there was no accident etc, and then said they would install a new airbag and module, and replace the corroded module connector if I would get the remaining leaking repaired by a body shop (they recommended), but they would not pay for the leak repair. The body shop said it would be about $2100 to remove the dash and properly repair the leak....The car is not worth that money with over 275,000KM.
So, they consented to the problem, but would not take ownership of the full repair. I must admit, other that that issue, the car had been fairly good for the miles I put on... (bought it at 2 years old with 17,000km).