The National Highway Traffic Safety Administration has launched an investigation of the 2016 Hyundai Sonata.
According to agency documents, at least four owners have reported driving the Sonata when its rear brakes locked. More alarmingly, these incidents allegedly occurred without the drivers pressing the car's brake pedal. One complaint even reported that the brakes caused a fire:
"REAR BRAKES FAILED TO PROPERLY FUNCTION WHILE THE VEHICLE WAS IN FORWARD MOTION ON A HIGHWAY. BOTH REAR BRAKES LOCKED UP WITHOUT OPERATOR PRESSING ON BRAKE PETAL. BOTH REAR BRAKES AND WHEEL GOT RED HOT CAUSING PASSENGER SIDE REAR BRAKES CAUGHT ON FIRE. NO BRAKE WARNING LIGHTS WAS ACTIVATE. THIS EVENT TOOK PLACE TWICE, ONCE ON 1/27/16 (18 DAYS AFTER PURCHASE) AND 2ND TIME 3/7/16...."
(Ed. note: sorry for the shouty caps. That's the way NHTSA rolls.)
The cause of the locking brakes remains uncertain. However, in May of 2016, Hyundai issued a technical service bulletin to dealers, asking them to fix a problem with the Sonata's electric parking brake software.
NHTSA says that the problem occurred after the software conducted a diagnostic self-check. In some cases, the routine could leave the Sonata's rear brake pads in contact with the brake rotors, causing them to "drag" when the vehicle was in motion.
The Sonata investigation is now in the Preliminary Evaluation phase, during which NHTSA will work with Hyundai to evaluate consumer complaints and identify possible causes for the brake problem. If they find a persistent issue, the investigation could move on to phase two, the Engineering Analysis, during which NHTSA will try to recreate the problem in a lab setting. Depending on the results of that phase, NHTSA could call for a full or partial recall of the 2016 Hyundai Sonata, which would affect roughly 8,000 vehicles in the U.S.
We'll keep you posted as the investigation progresses.