That means the computer has disabled the system and stored a diagnostic fault code. The most common problem is typically a broken clock spring under the steering wheel. That is a wound-up ribbon cable inside a plastic housing. As it continues to break apart, eventually the horn and cruise control also will stop working.
There are other possible causes of course but the clock spring is of my most concern simply because of the very tiny chance the air bag could pop accidentally. Every electrical connector between the computer and the air bag has shorting bars to connect the two wires together when any plug is disconnected. That is a safety feature to prevent deployment from static electricity. That is why you rarely hear of an air bag popping while a mechanic is working in the system. When the clock spring breaks, it's just like unplugging a connector but there is no shorting bar to protect it from static electricity.
For demonstrations, instructors use a 9 volt transistor battery to blow an air bag, so you know 9 volts is enough to "initiate" the burning of the rocket fuel pellet. In the car, that process is done with the 12 volt car battery. When you walk across the carpet in your house in winter and get a shock from touching the door ****, that is at least 3,000 volts. In some vehicles you can generate that same shock by sliding across the seat fabric. It's easy to see how that static electricity could fire the air bag. THAT is why the concern if the clock spring is broken. The break is inside a sealed housing so it is fairly well protected, but I did have one many years ago that had part of the ribbon cable peeking out from under the steering wheel. Most don't get that bad.
Wednesday, April 20th, 2011 AT 7:47 PM