brakes, seat belts, and airbags

[jessclear]

I have a general car safety question. If a car's brakes go out, will that cause the seat belts to not lock in the event of a collision? If that does cause the seat belts to fail, would the air bags also fail? I think the air bags are a different system, but are the brakes connected to the seat belts working properly in a collision? Just curious based on a recent accident I heard about.

[jen_nah]

The airbags are connected to your PCM and senors located at different points on the vehicle. So, No the breaks have nothing to do with airbags deploying.

The same goes with seatbelts too. A seatbelt locks up when the retractor become unlevel from the impact. I hope I am explaining this correctly. I am sure someone can get more technical then I can. But, No seatbelts are not connected the brakes either.

[AdventureMom]

Think about it a minute: if you turn you car on and hit the brakes without moving, seatbelts aren't locking and airbags aren't deploying... :p

It's a sudden change in motion that activates them. In our CPS course, we got to see the pendulum (?) with the weight that moves forward and triggers the locking mechanism on the seatbelt. Way cool. :cool:

[jessclear]

So in an accident where the brakes failed, the seatbelts didn't lock and the airbags did not deploy, three different systems in the car failed? This is speculation in the accident so far, but it is being investigated. We know for sure the airbags did not deploy, and it seems from the injuries that the seatbelts did not lock. We are unsure about the brakes, but eyewitness accounts seem to suggest the brakes may have failed to cause the accident. Just wanted to understand the mechanisms for myself. Thank you for the input. It makes more sense to me now.
BTW, no children were in this particular accident. Two adults were involved, one passed away and one is in ICU. It is under investigation, but for the sake of the airbags failing alone, I will say that the car was a 2006 Chrysler 300 with very few miles on it. I have found (online) that they have had a lot of problems with steering, brakes, and airbags on these cars lately. Please look into it if you or someone you know owns one of these cars. Just have the car checked to make sure your systems are in working order. I'm not trying to cause a panic, just informing of the possibility.

[southpawboston]

sometimes if the crash isn't just "perfect", the sensors will fail to deploy the airbags and/or seatbelt pretensioners.

remember that cars are designed to perform in standardized crash tests. they place the sensors and calibrate them so that the cars perform as well as possible *for the test that they will be subject to*. in real life, crashes are not as controlled and "perfect", so the sensors may not perform well if the majority of the crash force occurs somewhere far away from the sensors. that's also why you should take crash ratings with a grain of salt, and view crash test ratings collectively. the safest cars perform well in a wide variety of standardized crash tests that complement each other, not just one or two.

[jen_nah]

sometimes if the crash isn't just "perfect", the sensors will fail to deploy the airbags and/or seatbelt pretensioners.

remember that cars are designed to perform in standardized crash tests. they place the sensors and calibrate them so that the cars perform as well as possible *for the test that they will be subject to*. in real life, crashes are not as controlled and "perfect", so the sensors may not perform well if the majority of the crash force occurs somewhere far away from the sensors. that's also why you should take crash ratings with a grain of salt, and view crash test ratings collectively. the safest cars perform well in a wide variety of standardized crash tests that complement each other, not just one or two.

Very true!

To the OP
Also it depends on the type of crash for airbag deployment. Ex: Your front airbags will not deploy in a side or rear impact and side airbags will not deploy in a front or rear impact.

If brakes failed this could be why the seatbelts didn't lock due to the vehicle not pitching to allow the pendilum to become unlevel until "after" the impact had occur. Usually when a crash occurs the driver slams on the brakes causing the car to pitch forward making it unlevel & the seatbelt pendilum to then become unlevel and locking the seatbelts.

I hope they are able to find to cause of the accident and what a tragic accident.