Patrick G., Grand Junction, Colo.

Federal regulations do not specify a specific weight at which passenger-side airbags must be turned on or off. Instead, automakers must meet a performance standard that in a frontal collision the airbag protects a crash dummy that represents a “5th percentile female” and weighs about 108 pounds. Passenger-side airbags should be turned on when seat sensors detect an occupant of this weight or greater, but that doesn’t mean they will always be off if someone lighter is seated.

All airbag systems are not the same, so when the passenger-side airbag is turned on can vary by manufacturer and the readings from seat sensors that measure not only the weight but the stature and seating position of the occupant and other factors. For example, on some GM vehicles, an electronic field measures the amount of water in the occupant to help determine the occupant’s size and weight. The National Highway Traffic Safety Administration says an adult who is not centered and seated upright or is leaning heavily on an armrest can take pressure off the seat cushion and mislead the seat sensors. Ford_airbags

Even if the “passenger airbag off” warning light is not illuminated, the airbag should not deploy if the system senses a child or infant, who could be injured by the force of the deployment. If the “passenger airbag off” warning light doesn’t come on when you think it should (or does when it shouldn’t), NHTSA advises that you consult your owner’s manual and have the car inspected by a dealer if you are still concerned.

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Answered by Rick Popely on March 4, 2010 in How Safe is This Car? | Permalink

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