Dear Tom and Ray:

I drive a 2004 Hyundai Elantra that was bought used, and I don't know the history of the vehicle. Last evening, I unavoidably ran over a fairly large armadillo. It was big enough, and the car sits low enough, that it evidently struck the front bumper, which I understand triggers the air bags during a front-end collision. The air bag did not deploy; however, the air-bag light on the dash came on and remained on for the last five miles of the trip, making me very anxious. This morning when I started the engine, the air-bag light on the dash came on for the usual six seconds to indicate that the system is functional, and then went off. But is it functional? What happened?

-- Ginger

RAY: Luckily, armadillos are not on the list of air-bag-deploying mammals, Ginger.

TOM: I don't know the specifics of the air-bag system in your car, but I'm pretty sure there are two sensors in the bumper. And I suspect they're "inertial switches."

RAY: Unlike an old-style switch where the contacts get physically "pushed together," an inertial switch detects a very quick change in acceleration. For instance, were you to hit a 1,500-pound polar bear, your car would go from 50 miles an hour to zero in an instant. The inertial switch would register that and deploy the appropriate air bags.

TOM: But running over a small mammal, as disturbing as that might be, did not cause you to decelerate enough to trigger an air-bag deployment.

RAY: It DID, however, register as an "event" with the air-bag computer. The computer basically said: "Whoa! You guys feel that?" And that's what caused the light to go on. The light is a signal that the computer is no longer sure all is well with the air-bag system.

TOM: But, the next morning, the computer ran a self-diagnostic check of the air-bag system, like it does every time you start the car. That's when it confirmed that everything was working -- except for the armadillo -- and turned off the light. If you had pulled over and restarted the car right after the incident, the computer would have run a self-diagnostic check then, and the air-bag light would have gone off then, too.

RAY: So your air-bag system is functioning normally. Still, it would be worth asking your regular mechanic to have a look at the front of your car. Aside from armadillo parts, it's possible you did some mechanical damage in the front end that you don't know about, and your computer won't tell you that.