The U.S. government is investigating whether Hyundai and Kia moved quickly enough to recall more than 1.6 million cars and SUVs because the engines can stall, increasing the risk of a crash.
The National Highway Traffic Safety Administration says it's looking into three recalls by the Korean brands. The agency also says it's investigating whether the automakers followed safety reporting requirements.
Hyundai recalled about 470,000 vehicles in September of 2015 because debris from manufacturing can restrict oil flow to connecting rod bearings. That can cause bearings in the four-cylinder engines to wear and fail. The repair was an engine block replacement.
Last March Hyundai and Kia issued two more recalls covering 1.2 million additional vehicles with the same engine problem.
The companies say they're cooperating with the investigation.