General Motors faces an upgraded U.S. investigation and potential recall of 256,025 of its 2003 Chevrolet Cavalier and Pontiac Sunfire small cars because of taillight failures.

The U.S. National Highway Traffic Safety Administration and the auto maker received 614 complaints, including one accident with no injuries, the agency said on its website. The flaw may have occurred because a supplier didn't use a type of grease in the bulb socket that helps prevent electrical failures, the NHTSA said.

GM resumed using the grease last year and advised dealers this July to make sure it was applied to the bulb sockets, the NHTSA said.

"This is still in the investigation stage," said Jim Schell, a spokesman for Detroit-based General Motors. "We are trying to determine the reason for this." He declined to name the supplier that had stopped using the grease.