The contact's son owned a 2018 Hyundai Sonata. The contact stated while her son was driving at 68 MPH with a passenger in the front passenger seat, he noticed a burning odor and he noticed smoke coming inside the cabin through the AC vents. There was no further information provided. The contact's son pulled into a gas station and saw fire underneath the hood. The contact's son and the passenger immediately exited the vehicle. The contact's son was able to extinguish the fire with the assistance of bystanders who used fire extinguishers. The vehicle was towed to the dealer. The vehicle was not diagnosed or repaired. The vehicle was then repossessed by the auto financing bank. The manufacturer was notified of the failure and informed the contact that they could not assist as the failure was caused by a missing oil cap. The failure mileage was unknown.