This warning light illuminates:
Hyundai Sonata LF 2014-2019 Service Manual: Heater & A/C Control Unit (Manual) Repair procedures
Replacement
1.
Disconnect the negative (-) battery terminal.
2.
Using a screwdriver or remover, remove the center fascia panel (A).
3.
Disconnect the A/C & heater controller connectors (A).
4.
Remove the heater and A/C controller (A) from the center facia panel.
5.
Install in ...
Hyundai Sonata LF 2014-2019 Service Manual: Stop Lamp Switch Description and Operation
Description
The stop lamp switch plays the role of supplying signals to
turn on stop lamps and convenience devices (HECU,ECU,BCM,SMK etc.) for
drivers as a system that expresses the driver's intentions to brake by
pressing the brake pedal.
...