The auto industry’s airbag troubles deepened today, as federal regulators said three big automakers will recall about 2.1 million older vehicles to fix defects that could cause airbags to deploy when they are not supposed to.

Toyota Motor Corp (7203.T), Fiat Chrysler Automobiles NV (FCAU.N) and Honda Motor Co (7267.T) have issued three earlier recalls to fix problems with a defective chip in the affected airbag systems. But the National Highway Traffic Safety Administration said that "a small number of vehicles" fixed under those earlier actions had experienced inadvertent air bag deployments, hence the new recall.

An airbag going off suddenly could cause an accident, the agency said. There have been no known fatalities related to the problem, it said.

The latest air bag recalls were not related to a wider issue involving millions of vehicles recalled over Takata Corp (7312.T) air bags. U.S. safety regulators have said defective Takata air bag inflators in certain vehicles can rupture and spray metal fragments inside the vehicle.

NHTSA blamed the problems it reported on Saturday on "electrical noise" in the air bag system. The agency said a fully effective solution to the problem might not be available until late this year.