On most cars, the light can only be reset by reading the diagnostic fault codes and erasing them with a hand-held computer called a scanner. There is one thing you can do though. Ok, two things.
First, watch the light very closely when you turn on the ignition switch. The computer will do a system test for seven seconds, then the light will go out and the system is armed and ready to pop. One of two things is going to happen. If the light flickers off after seven seconds and comes right back on, the computer detected a problem and shut the system down. The most common fault on most cars is the clock spring under the steering wheel. That is a wound-up ribbon cable. It is needed to maintain a solid electrical connection as the steering wheel rotates. Years ago a simple sliding contact worked fine for the horn button, but there could be a microscopic piece of dirt that interrupts the electrical connection the exact millisecond the bag has to fire. That's why they use the ribbon cable. As the cable continues to break, eventually the horn and cruise control won't work either.
The other thing the light might do is not flicker off and back on. I suspect you are going to find it stays on steady. That is the clue the self test was not performed. This would be typical of a blown fuse due to a surge caused by connecting your new battery. Normally there are no defective parts, and no damage done other than the fuse. There are actually two air bag fuses, but they might not be labeled as such. There has to be a backup circuit to turn the light on. If there were only a single fuse and power circuit, there would be no power to turn the light on if it blew.
Those fuses might be inside yellow pull handles in the fuse box, and you might have to snap the cover off to be able to pull the fuse out or to touch a voltmeter's test probe to the terminals. Look for other stuff that doesn't work. Sometimes the air bag fuse is tied in with something else that people are more likely to notice such as interior lights or the radio.
Sunday, March 21st, 2010 AT 12:39 AM