To open:
Push and release the cover and the holder will slowly open. Place your sunglasses in the compartment door with the lenses facing out.
To close:
Push back into position. Make sure the sunglass holder is closed while driving.
WARNING
Hyundai Elantra AD (2016-2020) Owners Manual: Hill-Start Assist Control (HAC)
The Hill-Start Assist Control (HAC) helps prevent the vehicle from rolling backwards
when starting a vehicle from a stop on a hill. The system operates the brakes automatically
for approximately 2 seconds and releases the brake after 2 seconds or when the accelerator
pedal is depressed.
WARNI ...
Hyundai Elantra AD (2016-2020) Service Manual: Repair procedures
Inspection
1.
After disconnecting the vapor hose from the PCV valve, remove the PCV valve.
2.
Reconnect the PCV valve to the vapor hose.
3.
Run the engine at idle, then put a finger over the open end
of the PCV valve and make sure that intake manifold vacuum can be felt.
  ...