The following was said on the Nissan Forums as well. I'd take it with a pinch of salt, but apparently it worked for them:
Here's the process to reset the air bag light (copied from somewhere else on the forum)... I tried it and it works.
If you have the airbag light, it will show steady for a few seconds (the manual says 7 secs) after you turn the key from off to on (but not start) and then start to flash. Here is how to reset it:
1. Turn the key from off to on.
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.
If it does not work the first time, just repeat the steps again.
Also check the connections under the drivers seat or the connections to the seat belt pre-tensioner
benzerf, August 2009