The National Highway Traffic Safety Administration, the top U.S. auto safety regulator, said on its website an estimated 2.8 million Harman Kardon "infotainment" systems may be affected - - double the number specified in the Fiat Chrysler recall announced July 24.
The Harman Kardon investigation was opened on July 29, according to the agency. Company officials were not immediately available for comment.

NHTSA chief Mark Rosekind said on Friday that his agency is trying to find out how many automakers may have received radios from the same company that supplied Fiat Chrysler, Reuters reported, adding that Rosekind didn't identify the supplier.

Harman Kardon's website shows it provides sound systems for automobiles including BMW, Subaru, and Mercedes-Benz, as well to Fiat Chrysler.

The inquiry "is being opened to obtain information from the supplier of Chrysler Uconnect units to determine the nature and extent of similarities in other infotainment products provided to other vehicle manufacturers," NHTSA said.