If your vehicle is showing airbag warning light stays illuminated constantly, here are the most likely causes and the parts you'll need to fix each one.
The yellow airbag connectors under the front seats are easily bumped loose by vacuuming, moving the seat to its limits, or storing items underneath. This is also a common error if the seats were recently removed for cleaning or audio work without disconnecting the battery first.
The microswitch inside the seat belt buckle that detects if you are strapped in can fail due to daily wear, spilled drinks, or debris. If the system cannot verify the belt status, it disables the airbag and triggers the light.
The clockspring is a coiled ribbon cable behind the steering wheel that maintains the electrical connection to the driver's airbag as the wheel turns. Over time, this ribbon can snap, often taking out the horn and steering wheel controls as well.
The weight sensor inside the passenger seat determines if a child or adult is sitting there to adjust airbag deployment. These sensors can fail, become uncalibrated, or get damaged by kneeling heavily on the seat cushion.
The airbag control module is highly sensitive to voltage drops. A weak battery or failing alternator can cause the voltage to dip low enough during engine cranking to trigger a persistent airbag warning light.
Impact sensors located behind the front bumper or inside the door shells are exposed to the elements. Water intrusion, road salt corrosion, or minor parking lot bumps can damage these sensors and trigger the warning light.