Check your tires, including the spare tire, once a month or more.
How to check
Use a good quality tire pressure gauge to check tire pressure. You can not tell if your tires are properly inflated simply by looking at them. Radial tires may look properly inflated when they are under-inflated.
Remove the valve cap from the tire valve stem. Press the tire gauge firmly onto the valve to get a pressure measurement. If the cold tire inflation pressure matches the recommended pressure on the tire label located on the driver's side center pillar or in this manual. No further adjustment is necessary. If the pressure is low, add air until you reach the recommended pressure. Make sure to put the valve caps back on the valve stems. Without the valve cap, dirt or moisture could get into the valve core and cause air leakage. If a valve cap is missing, install a new one as soon as possible.
If you overfill the tire, release air by pushing on the metal stem in the center of the tire valve. Recheck the tire pressure with the tire gauge. Be sure to put the valve caps back on the valve stems. Without the valve cap, dirt or moisture could get into the valve core and cause air leakage. If a valve cap is missing, install a new one as soon as possible.
A cold tire means the vehicle has been sitting for 3 hours and driven for less than 1 mile (1.6 km) in that 3 hour period.
Allow the tire to cool before measuring the inflation pressure. Always be sure the tire is cold before inflating to the recommended pressure.
Hyundai Elantra AD (2016-2020) Service Manual: Variable Intake Solenoid (VIS) Valve Description and Operation
Description
Variable Intake manifold Solenoid (VIS) valve is installed on
the intake manifold. The VIS valve controls the vacuum modulator which
activates a valve in the intake manifold. The ECM opens or closes this
valve according to engine condition (Refer to below table).
Engine cond ...
Hyundai Elantra AD (2016-2020) Service Manual: Troubleshooting
Troubleshooting
Ignition System
SymptomSuspect AreaRemedyEngine will not start or is hard to start (Cranks OK)Ignition lock switchInspect ignition lock switch, or replace as requiredIgnition coilInspect ignition coil, or replace as requiredSpark plugsInspect spark plugs, or replace as requir ...