Airbags are meant protect a driver or passenger in the event of a collision, but the only way for those safety devices to actually cushion a person from the impact of a crash is if the device activates. Apparently that hasn’t been happening in some Subaru sedans, leading the National Highway Traffic Safety Administration to initiate a probe into the problem.

NHTSA’s Office of Defects Investigation opened an investigation into 33,500 model year 2012 Impreza sedans after receiving 26 vehicle owner complaints involving the non-deployment of the passenger airbag, despite a passenger being present.

According to the NHTSA investigation notice [PDF], the Impreza’s occupant detection system – which activates and deactivates the passenger seat airbag system depending on the weight of the occupant – at times fails to operate correctly.

If the system fails to detect a present passenger, the airbag may not deploy in the event of a crash, increasing the risk of injury to the occupant.

Reports submitted by vehicle owners say the system often incorrectly turned off the front passenger airbag when the seat was occupied.

“The dashboard ‘airbag malfunction’ light turns on and the passenger airbag light switches to ‘off’ while there is a passenger in the car,” one complaint states. “This probably means that if there was a collision, the passenger airbag would not deploy,with passenger in front seat. It was happening about 40% of the time that I had a passenger in the front seat.”

“When someone sitting in the front passenger seat leans slightly, the airbag sensor frequently malfunctions and the car turns off the airbags for that seat, as indicated by the lighted dashboard indicator sign,” another owner writes to NHTSA.

NHTSA has received no complaints regarding actual crashes or injuries related to the airbag issue.

Back in May 2012, Subaru published a technical service bulletin to address conditions that may lead to the passenger seat airbag turning off when the seat is occupied, NHTSA reports.

Investigators say they will assess the scope, frequency, and consequence of incorrect air bag suppression, as well as determine if any connection exists to the prior service bulletin.

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