During the operation of my 2023 GMC Yukon XL AT4 on [XXX], carbon monoxide (CO) entered the cabin, exposing my children and me to dangerously high levels of CO and causing confirmed carbon monoxide poisoning. We were driving with the engine running and the heater on for approximately 21 minutes when the exposure occurred. Symptoms began to escalate that day and into the proceeding days, including severe headache, stomachache, pallor, chest pressure, shortness of breath, fatigue, and neurological issues. My children, particularly my [XXX] and [XXX] , experienced the most severe effects’ both were very ill especially my [XXX] . Unfortunately, we initially did not believe it was possible for CO to enter the vehicle cabin, which delayed early intervention and appropriate medical care. Blood testing 4 days later confirmed elevated carboxyhemoglobin levels in my [XXX] , the only one tested. During the incident, the battery warning light was the first indication of trouble, but soon after, many additional error messages began flashing on the dashboard. The vehicle then overheated, decelerated, and eventually shut down while driving. We were in the vehicle under 21 minutes. Upon inspection after the incident, my husband noted a severed belt and potential pulley issues. The exact cause of the CO intrusion has not yet been identified. The vehicle is available for inspection and unaltered to preserve evidence. I am writing GMC and requesting further investigation by GMC. This incident reflects a severe safety issue with potentially life-threatening implications for GMC owners. CO exposure can cause significant harm, and delayed identification in this case placed my family at substantial risk. Immediate investigation and corrective action are essential to prevent similar incidents from occurring in the future. Time is critical, as this defect could have catastrophic consequences for other unsuspecting drivers and their families. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)