According to published reports, the National Highway Traffic Safety Administration will say replacement bags installed in the past three years may fail or not inflate properly.
The agency is asking car owners to check a government website, http://www.safercar.gov/, or call their manufacturer or local dealership to see if their vehicle model is among those for which counterfeit airbags have been made.
The NHTSA says tens of thousands of cars may be affected.
No deaths or injuries have been tied to the counterfeit bags, but it's unclear accident investigators would be able to identify a counterfeit bag from a genuine one.
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