If the Smart Key is not working properly, try replacing the battery with a new one.
Battery Type: CR2032
To replace the battery:
1. Pry open the rear cover of the smart key.
2. Remove the old battery and insert the new battery.
3. Reinstall the rear cover of the smart key.
If you suspect your smart key might have sustained some damage, or you feel your smart key is not working correctly, contact an authorized HYUNDAI dealer.
Information
An inappropriately disposed battery can be harmful to the environment and human health. Dispose the battery according to your local law(s) and regulation(s).
Hyundai Sonata LF 2014-2019 Owners Manual: Owner Maintenance Schedule
When you stop for fuel:
Check the engine oil level.
Check coolant level in the engine coolant reservoir.
Check the windshield washer fluid level.
Check for low or under-inflated tires.
WARNING
Be careful when checking your engine coolant level when the engine is hot.
This may result in coolan ...
Hyundai Sonata LF 2014-2019 Service Manual: Refrigerant Line Repair procedures
Replacement
1.
If the compressor is marginally operable, run the engine at
idle speed, and let the air conditioning work for a few minutes, then
shut the engine off.
2.
Disconnect the negative (-) battery terminal.
3.
Recover the refrigerant with a recovery/charging station.
4.
...