DETROIT (AP) - Federal safety regulators are trying to determine if more automakers used defective side air bags that have caused recalls of some Toyota, Honda, Nissan and Subaru vehicles.

The National Highway Traffic Safety Administration says on its website that it started investigating last week because the air bags may not inflate in a crash.

The problem has caused recalls of more than 2,700 vehicles, but that could grow if more automakers used the bad parts.

Recalled vehicles include 427 Toyota RAV-4s; 974 Honda Accords, Civics, Crosstours and Acura MDXs; 381 Subaru Legacys and Outbacks; and 976 Nissan Altimas and Versas.

Safety regulators say the vehicles may have an incorrect mixture of the gas that inflates the side curtain air bags in a crash. So far no one has been hurt.