The airbag light comes on when the backup battery is drained or damage has occurred to the clock spring or the airbag module. Because the light can have many causes, a technician must diagnose the problem if the light stays on.
When the car battery drains, the airbag's backup battery also drains, causing the light to appear. Recharging or replacing the car battery usually recharges the backup battery, although the light sometimes stays on because the system records an error code. The clock spring is a circuit band that connects the airbag with the steering wheel, and the spring may deteriorate over time, causing an error code. The airbag module controls when to deploy the airbag, and its position beneath the car makes it susceptible to moisture damage.