Federal regulators have indicated they are worried that Nissan’s recall last year of almost one million vehicles did not correct a malfunction of the passenger airbag, raising the possibility that the automaker might have to recall the vehicles again. 

The vehicles were recalled in March 2014 because a computer program could misjudge the weight of the person in the front passenger seat and conclude that a child instead of an adult was sitting there.

The airbag is not supposed to deploy if a child is in the seat because of the risk that the airbag can cause serious injuries, safety researchers have concluded. But the failure to deploy for an adult could have the opposite effect, resulting in more serious injuries.

Nissan said it would reprogram the software that controls the passenger-side airbag in the initial recall. But the National Highway Traffic Safety Administration has received almost 1,300 complaints from owners whose vehicles were repaired under the recall but still see a warning light indicating the airbag is off even when an adult is in the seat, according to an agency report dated Aug. 31 and posted last week on its website.

Those complaints prompted the agency to intensify an investigation started in March. The agency said it would “further evaluate the effectiveness of the recall remedy, which will include a thorough review of the countermeasures taken by Nissan and its suppliers.” That could lead to the agency to pressure Nissan for a new recall with a new fix.

“My Pathfinder has been at the dealership four times to correct the NHTSA recall 14V-138,” one owner wrote to the agency in May 2014. “This problem has not been resolved. I feel this is a safety issue.”

The recalled vehicles are the 2013 Infiniti JX35; 2014 Infiniti Q50 and QX60; 2013-14 Nissan Altima, Leaf, Pathfinder and Sentra; and the 2013 Nissan NV200. By the end of June, the automaker told the safety agency, it had repaired almost 839,000 of the 990,000 vehicles recalled.

Steve Yaeger, a Nissan spokesman, said in an email that the automaker “believes the recall remedy was effective and appropriately addressed the safety defect.”

The safety agency has been criticized by congressional committees and the Department of Transportation’s inspector general for slowness at recognizing and acting on safety defects and for hesitating to use its authority.

But consumer advocates say the agency has become far more aggressive under Mark R. Rosekind, who took over in December as administrator.