While driving on a highway in April 2025, my 2017 Hyundai Santa Fe Sport suddenly lost all power after approximately 10 minutes of normal driving. All dashboard warning lights illuminated, and both the accelerator and brake pedals became unresponsive. I was forced to stop the vehicle using the handbrake in the middle of a 65 mph highway, creating an extremely dangerous situation for myself and other drivers. Prior to this incident, the vehicle had displayed the P1326 knock sensor code multiple times over a 10-month period, each time accompanied by hesitation when accelerating. The knock sensor was replaced twice under used car warranty by Honda. Despite these interventions, the same code and symptoms recurred. The Hyundai dealership(Dec 2024 at Montgomery, Jan 2025 at Enterprise) repeatedly stated that there was aœnothing wrong with the engine.a After the highway failure, the vehicle was inspected by a collision center and an independent mechanic. They confirmed that Cylinder 4 had no compression and diagnosed a burnt valve. Full engine replacement was recommended. Hyundai initially indicated that the engine might be covered under the extended warranty but later denied the claim, stating that the damage was due to a cylinder issue and can not check bearing failure. They also claimed it was too late to determine whether the bearing was the cause. This is not an isolated issue. Many Hyundai owners across the U.S. have reported identical symptomsa”P1326 code, hesitation, cylinder compression loss, and ultimately engine failurea”particularly in vehicles equipped with the Theta II engine. These failures often occur around or after 100,000 miles, despite regular maintenance. This ongoing and widespread cylinder-related engine failure presents a serious safety risk and must be addressed through manufacturer accountability, improved diagnostic standards, and proactive repair or recall efforts.