A day after federal safety regulators warned owners of recalled vehicles with defective airbags to “act immediately” and get them replaced because they could explode, consumers on Tuesday were left grasping for answers.

A link from the website of the National Highway Traffic Safety Administration that lets owners look up their car by vehicle identification number did not respond all day. Calls to an operator on the agency’s hotline — 1-888-327-4236 — were routinely put on hold.

And many owners who tried to get their cars fixed were turned away because the parts, made by the Japanese supplier Takata, were simply not available.

At issue is a faulty propellant inside air bags that is unstable and can explode even after a minor accident, sending metal shards flying into the cabin. The defect has been linked to at least three deaths and more than 100 injuries.