The contact owns a 2015 Kia Optima. The contact stated that while driving at an undisclosed speed, he smelled a burning odor permeating throughout the interior of the vehicle, prompting him to discontinue driving the vehicle. After a visual inspection of the exterior of the vehicle, the contact observed what appeared to be a hydraulic fluid leak underneath the engine compartment. The check engine warning light was illuminated. The vehicle was not taken to the dealer or an independent mechanic. The vehicle was not repaired. After investigating the failure, the contact related the failure to NHTSA Campaign Number: 21V331000 (Service Brakes, Hydraulics); the VIN was included, but the vehicle had not yet been repaired. The manufacturer was not notified of the failure. The failure mileage was 160,000.