I had this problem when I added a sub, wiring and stuff. Did you have your battery disconnected? I'm not sure what set's it off (other than pulling things apart) but at some point you will likely end up with a flashing airbag sensor light. Here is how to reset it yourself.
1. Turn the key from off to on. But dont start the car.
2. Watch the airbag light closely. It will stay on for a few secs. and then as soon as it blinks off (the start of the flashing), turn the key off instantly.
3. Count to 5 (1 Mississippi, 2 Mississippi . . . .)
4. Repeat steps 1-3 two more times until you have done the cycle three times.
5. Now turn the key on and watch the light. It will start blinking in a different, slower manner. This is diagnostic mode. You can watch this for a little while, no hurry.
6. Now turn the key off again, Count to 5 like in step 3 again, and turn back on. If the procedure worked, the airbag light will not be flashing.
This didnt work for me the first few times, and my g/f was VERY skeptical and tired of waiting for me to do it again, but to our amazment it worked. Follow the steps!
That dosnt look so hard...
03 Black SE. stock