The National Highway Traffic Safety Administration on Aug. 6 opened an investigation into an estimated 553,692 Subaru Forester vehicles manufactured by Subaru of America Inc., the U.S. arm of Japanese carmaker Subaru Corp.

The NHTSA's Office of Defects Investigation, or ODI, will probe 2016-2018 Subaru Forester SUVs over concerns that the vehicles' front passenger airbags may malfunction, causing them to not operate as intended.

The investigation was triggered after the agency received 51 complaints and additional early warning report data, alleging that the front passenger seats' occupant detection system, or ODS, may fail to operate properly when the front passenger seat is occupied by a full-sized passenger.

A suppressed airbag may increase the risk of injuries in the event of a crash, according to the document.

There have been no reports of crashes, fires, injuries or fatalities linked to the defect.