The software update is designed to protect the vehicles from engine damage, and new extended warranties will be offered for engine problems, they said.

Hyundai said its newly developed "knock sensor" software monitors engine vibrations for any signs of excessive wear on the connecting rod.

"Hyundai has issued a subsequent recall to ensure the safety of customers," Hyundai said in a statement issued by its American unit. "The recall is being conducted to inspect and confirm proper reinstallation of the fuel tube to the high-pressure fuel pump."

The US National Highway Traffic Safety Administration has been investigating Hyundai and Kia to determine whether initial recalls were carried out properly.

Hyundai voluntarily recalled more than 1 million vehicles in 2015 and 2017 to address the issue of engine failures.

Hyundai and Kia are the flagships of Hyundai Motor Group, the world's fifth carmaker by sales. (Yonhap)