Consumers were left in confusion Tuesday over air bags at risk of rupture, with federal auto safety regulators urging owners of more than five million vehicles to "act immediately" to get them replaced, and automakers insisting that many replacement parts are simply not available.

But just finding out whether a car needs to be repaired was proving difficult for many owners.

A link from the website of the National Highway Traffic Safety Administration that allows consumers to look up their car by vehicle identification number was not responding, and calls to an operator on a hot line — 1-888-327-4236 — were put on hold. The agency did not immediately respond to a request for comment.

Besides the agency's website, a nationwide clearinghouse for recall information that covers vehicles registered in the United States, most automakers allow searches by vehicle identification number, including those covered in Monday's warning: Honda, Toyota, Nissan, Mazda and BMW.

Chrysler, Ford, Subaru and Mitsubishi also have recalls for the same problem with Takata air bags, but their vehicles were not listed in the warning by regulators. The agency said it was still completing its list.

At the heart of the defect is faulty propellant inside the air bag that is unstable and can explode, sending metal shards flying into the cabin. The faulty air bags have been linked to at least three deaths and more than 100 injuries.

Some safety experts prohibit automakers from disabling air bags. But David Friedman, deputy administrator of the National Highway Traffic Safety Administration, said in an interview Monday evening that because of the seriousness of the air bag defect, the agency was condoning the move.

NEW YORK TIMES