This warning light informs the driver that the seat belt is not fastened.
Hyundai Sonata LF 2014-2019 Service Manual: Side Airbag (SAB) Module Repair procedures
Removal
The side airbag cannot be disassembled from the seat back
assembly, so replace the seat back assembly when replacing the side
airbag.
1.
Disconnect the battery negative cable and wait for at least 3 minutes before beginning work.
2.
Remove the front seat ...
Hyundai Sonata LF 2014-2019 Owners Manual: Immobilizer System
The immobilizer system protects your vehicle from theft. If an improperly coded
key (or other device) is used, the engine's fuel system is disabled.
When the ignition switch is placed in the ON position, the immobilizer system
indicator should come on briefly, then go off. If the indicator starts ...