The only symptom a defective airbag has is an illuminated SRS light. The SRS light turns on when there is something wrong with the safety restraint system, or airbag unit. When this light turns on, the SRS will not allow the airbag to deploy if the car is in an accident.
If the SRS light is turned on, reset it using the manufacturer's procedure. The procedure may require a technician in order to reset it, so be ready to bring the vehicle into a service center if necessary.
In order to find the root problem of the airbag light, automobile manufacturer's procedures may allow the light to act as a code reader. Use this light to find out the problem with the airbag system, and then take the vehicle to be fixed.