The hazard warning flasher serves as a warning to other drivers to exercise extreme caution when approaching, overtaking, or passing your vehicle.
It should be used whenever emergency repairs are being made or when the vehicle is stopped near the edge of a roadway.
To turn the hazard warning flasher on or off, press the hazard warning flasher button. The button is located in the center fascia panel. Both the left and right turn signal lights will flash simultaneously.
Hyundai Elantra AD (2016-2020) Service Manual: Speakers Repair procedures
Inspection
1.
Troubleshooting for Speaker
(1)
Basic inspection of speaker
Inspect the sound from speaker after verifying that the
speaker mounting screws is removed and the wiring connector is connected
precisely to remove vibration transmitted from body trims and
surrounding parts.
...
Hyundai Elantra AD (2016-2020) Owners Manual: Climate Control Additional Features
Automatic Ventilation (if equipped)
When the ignition switch is in the ON position or when the engine is running
and temperature is below 59°F (15°C) with the recirculated air position selected
more than five minutes, the air intake position will automatically change to the
outside (fresh) ...