The NHTSA said most of the vehicles with the faulty bags had the originals replaced over the last three years by repair shops other than new car dealerships. Tens of thousands of car owners may be driving vehicles with the counterfeit airbags, according to the agency.
In government tests last month of 11 counterfeit bags, 10 didn't inflate or failed to inflate properly. In one test, a counterfeit bag shot flames and shards of metal shrapnel at a crash dummy instead of inflating, said NHTSA Administrator David Strickland, who showed a video of the test at a news conference.
The counterfeit airbags are marketed to repair and body shops as authentic. They may include a manufacturer's logo. Auto dealerships are generally required to purchase straight from the automakers, so counterfeiting is not an issue there.
NHTSA investigators believe many of the counterfeit airbags are made and shipped from China.
NHTSA has compiled a list of dozens of vehicle makes and models for which counterfeit airbags may be available, but the agency cautioned that the full scope of the problem isn't clear yet and the list is expected to "evolve over time."
If a car model is on the list and has had its airbags replaced during the past three years by a repair shop other than a new car dealership, NHTSA is asking owners to take the vehicle into a dealership or repair shop to be inspected at their own expense to determine whether the replaced airbags are counterfeit.
Fees for checking out airbags - a complex and technical process - could run between $100 to $200, said Bailey Wood, a spokesman for the National Automobile Dealers Association, said. The cost of replacing a driver's side center column airbag is $750 to $1,000, he said. Other airbags may be more, he said. Some types of cars have as many as eight airbags.
NHTSA is asking car owners to check a government website, www.Safercar.gov, for information on how to contact auto manufacturer call centers to learn if their vehicle model is among those for which counterfeit airbags are known to have been made.
Only 0.1 percent of the U.S. vehicle fleet - about 250,000 cars on the road - are makes and models for which counterfeit airbags are known to be available, NHTSA said.
About 2,500 counterfeit airbags have been seized by law enforcement authorities so far this year, John Morton, director of U.S. Immigration and Customs Enforcement, told reporters. Investigations are under way in several locations around the country, and further arrests and seizures are expected, he said.
The Associated Press contributed to this report.