Sir,
May I suggest that you check your owner"s manual. 2018 Hyundai Sonatas come with the "Lane departure feature" which is part of an ADAS system.

 

It is a Sport Model. ADAS is not available on this car.

 

I don't know where you are obtaining your info, but ALL 2018 Hyundai Sonatas came with some of the ADAS features. They are considered a Safety feature !
Has the vehicle had any type body work done on it?
There are sensors on the windshield, the Grille, front and rear bumpers and sides of the vehicle. If any one of them has been altered whether knowingly or unknowingly the system will not work correctly and your vehicle may be displaying this.

 

I meant to say that the car does not have lane assist. So obviously, that is not the problem. P.S. The cars that do have it, have a camera on the windshield not a sensor.

 

Trying to be as understanding as possible, your observations are inaccurate. Please do a little more research on how Lane assist works and you will find it does use a sensor.

 

Actually my observations are correct. Lane assist uses a sensor. Lane keep assist used a camera. They are two different things. Thanks.

 

What a difference one word can make !

Don't know if all 2018 Hyundai vehicles have this problem.
Unfortunately, some dealerships don't have the best trained techs. Have you consulted with a different dealership to see if they could help or get an answer to the problem?

 

After a ton of research, I believe the problem my be Tramlining.

 

So, do you believe you have over inflated tires?
When the car drifts, does it always drift to the same side?
If it does then could be alignment?

 

Tire pressure is fine. Alignment is fine. (checked twice) Drifts left and right.