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There are very many things that could be turning the airbag light on and it's something you'll want to get repaired as soon as possible.
The first thing that will need to be done is use a scan tool see what fault codes are stored in the airbag control module. There will be stores fault codes that will give a starting point for diagnosis.
There are many things that can turn the light on. It could be anything from the module itself to the airbags, side airbags, knee blocker airbag, clockspring, impact sensors, and wiring to any of the components in the system.
One of the more common problems is a broken clockspring. This is under the steering wheel and makes electrical contact between the wheel and steering column.
Another more common problem is corrosion in the front impact sensors. The sensors themselves and the terminals in their connectors will corrode and cause the airbag light to come on. There was a recall for this problem.