SEOUL -- South Korea's top automaker Hyundai Motor Co. and affiliate Kia Motors Corp. are voluntarily recalling a total of 478,000 cars in the United States due to problems with a valve used to prevent fuel leakage, Reuters reported Friday. A Hyundai official estimates that replacing the valves will cost between $4 million to $5 million. Hyundai Motor Co. issued recalls for 264,000 Sonata and Elantra models, while Kia recalled 214,000 of its Optima and subcompact Rio models. The recall came just a few days after Hyundai's hot-selling Sonata became the first Korean model to take top spot in U.S. research firm J.D. Power's rankings of initial quality. The recalls represented 66 percent of Hyundai's sales in 2003 and 90.1 percent of Kia's U.S. 2003 sales, a Hyundai official told the news agency. Hyundai Motor has set a 2004 U.S. sales target of 450,000 units after selling 400,000 units last year.