OUR 2015 YUKON XL DENALI CAUGHT FIRE IN THE ENGINE COMPARTMENT WHILE WAITING AT STOP LIGHT ON SAT, WITH MY WIFE AND CHILDREN INSIDE. IT WAS A HOT DAY, OVER 95 DEGREES, AND WE WERE TURNING LEFT ACROSS TRAFFIC WHEN WE REALIZED THE SMELL AND SMOKE WAS COMING FROM OUR VEHICLE. SMOKE WHIFFED FROM UNDER THE HOOD AND NOXIOUS FUMES FILLED THE PASSENGER COMPARTMENT, SCARING ME AND MY FAMILY. WE FINISHED THE TURN AND IMMEDIATELY PULLED OVER, SHUTOFF THE TRUCK, AND ALL ESCAPED FEARING IT WOULD BURST INTO FLAMES. WHATEVER WAS BURNING APPEARED TO STOP ONCE THE IGNITION WAS OFF. I OPENED THE DRIVER DOOR, POPPED AND RAISED THE HOOD TO LOOK FOR THE PROBLEM. I COULD SEE THAT A BELT, BEHIND THE SERPENTINE BELT, HAD SNAPPED, AND THERE WAS CHARRED DEBRIS ON THE EXPOSED MECHANICAL PULLEY FOR THE AC COMPRESSOR. AFTER FURTHER INSPECTION, I RESTARTED THE TRUCK WITH THE AC OFF, AND MONITORED FOR SMOKE. THE TRUCK SEEMED OK TO DRIVE HOME , SO WE DID WITHOUT AC ON A 95 DEGREE DAY. ON MONDAY WE DROVE THE TRUCK TO A TRUSTED MECHANIC FOR INSPECTION. THEY DIAGNOSED THE COMPRESSOR SEIZED AND ESTIMATED REPAIRS WERE $1,240. THE TRUCK IS GARAGED KEPT, AND GENTLY USED WITH ONLY 37,500 MILES. WE PURCHASED THE GMC CERTIFIED TRUCK IN JULY 2018 FROM A DEALER. I CREATED AN ACCOUNT ON GMC.COM & LOOKED THROUGH WARRANTY COVERAGE. A SPECIAL COVERAGE HAD BEEN EXTENDED FOR AC DEFECTS, BUT IT LAPSED IN MARCH, 2020. LOOKING FURTHER; MANY THOUSANDS OF GM OWNERS HAD SAME PROBLEM FROM SAME DEFECTIVE