General Motors is recalling 303,000 2009-10 Chevrolet Impalas because the front seat belts could come loose in a crash. The recall comes more than a year after GM first learned of the problem, The New York Times reported.

The automaker told the National Highway Traffic Safety Administration that the problem is t“from an assembly error.” The automaker said in its report to the agency that it had first learned of the problem in June 2009, after “nine reports of seat-belt warranty repairs that involved separation.”

GM said that there were some additional warranty claims in July and it investigated, leading to the recall. Under federal regulations, after discovering a safety defect, automakers have five business days to notify the safety agency and conduct a recall or face civil penalties.

A GM spokesman, Alan Adler, wrote in an e-mail: “The belief was that the potential for the condition to occur was only in the first three months of production. July, August and September of 2008. We were looking at data in June 2009. We believed that if a separation was going to occur, it would happen relatively quickly. Since the vehicles were built many months earlier and we had no other reports, we concluded there were no other vehicles with the condition.”

The automaker told NHTSA it had no reports of injuries or fatalities related to the defect.