OT: 2002 Mazda Protege 5 system, Anyone know about these? Options

[bondo]

My sister in-law has an 02 Protege 5 and her airbag light is on. Some shop quoted her something over $500 to fix it, and they insisted that the problem is because of damage to the right rear door. I think it's BS, because the damage is at the very top front of the door, and is just a deep scratch/dent done at about 1mph backing out of a parking spot (scraped a latch sticking out of a fence next to a driveway). It's about 1/4" deep and there was no impact involved. I also have trouble believing that anyone would put an airbag sensor in a door (which could get slammed).

She has 2 small children, and really should have a functioning airbag system in her daily driver. (kids ride in the back of course) Does anyone know how to troubleshoot these systems, or at least know where the sensor is? I'm going to be down in that neighborhood next week and would like to fix it while I'm there.

Thanks in advance!


Edit: Doh, should be Protege 5 AIRBAG system in the topic, but I can't seem to edit the title.