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Old 31st January 2010, 16:10   #1
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Default seat belt warning, how..?

Hey guys.
I am stupid but i never understood how the car understands that the passenger seat is occupied when you start driving with a passenger.
I mean, in a high end or passenger seat belt warning enabled car, if you are driving alone the passenger seat belt warning doesnot come up but if you have a passenger in the seat the passenger seat belt warning lights up. ( correct me if i am wrong)
I can understand for driver seat the warning is by default and once you engage the seat belt the circuit is complete and the warning light goes off.
But can someone throw some light on how the car gives warning for passenger seat belt.
regards
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Old 31st January 2010, 17:19   #2
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The front passenger seat has a weight sensor.

When a person sits on the seat and the sensor activates the seatbelt warning..
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Old 31st January 2010, 18:44   #3
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Even airbags use this sensor. Some cars wont deploy the airbag if it doesn't sense pressure beyond a specified weight. So even if a child (lighter than the specified weight) is sitting on the front seat, the airbag is programmed not to deploy.

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Old 31st January 2010, 23:37   #4
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Quote:
Originally Posted by Shan2nu View Post
Even airbags use this sensor. Some cars wont deploy the airbag if it doesn't sense pressure beyond a specified weight. So even if a child (lighter than the specified weight) is sitting on the front seat, the airbag is programmed not to deploy.

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@Shan2nu,
I have a question, some cars have a button for enabling the passenger airbag. If it is enabled via sensor why this button is required? Does it function as a master switch?

Thanks,
Vijay
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Old 1st February 2010, 03:03   #5
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I dont think cars that use sensors in the seat need have this switch. The sensors decide whether the airbags should or shouldn't deploy.

This might help - Q&As: Airbags

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Old 1st February 2010, 08:30   #6
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Thanks for info guys,
so technically speaking, if one puts some heavy weight on the passenger seat, the sensor will get activated and the warning will come on. right??
regards
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Old 1st February 2010, 08:50   #7
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Quote:
@Shan2nu,
I have a question, some cars have a button for enabling the passenger airbag. If it is enabled via sensor why this button is required? Does it function as a master switch?

Thanks,
Vijay
In my linea too i can activate and deactivare passenger airbag in the MID menu
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Old 16th November 2015, 11:42   #8
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Default Re: seat belt warning, how..?

Is it possible to install an audible seatbelt alarm in a car which didn't come with one?

The 2010 Manza Aura doesn't have airbags so it won't have the weight sensor. However, Aura+ came with airbags and I was wondering if the seatbelt warning system from that could be installed on an Aura.
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Old 16th November 2015, 11:54   #9
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Default Re: seat belt warning, how..?

If it's just an audible warning through a buzzer that you need, you can get it done by replacing the seatbelt anchor that comes with the normally-closed switch. Connect it to a 12 V supply from the fusebox that turns on with the ignition and a 12 V buzzer, you're done. Once you holster the seatbelt, the switch is open and this disables the buzzer.

The weight sensor is usually provided for the co-driver seat.
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Old 16th November 2015, 15:30   #10
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Default Re: seat belt warning, how..?

Quote:
Originally Posted by zipzapzoom View Post
... so technically speaking, if one puts some heavy weight on the passenger seat, the sensor will get activated and the warning will come on. right?? ...
Wrong. Weight sensing seats won't give out a warning if an adult (or a 'large' child) is sitting in the passenger seat. In fact, it won't give any warning if no one is sitting in it.

If the Airbags ECU thinks that someone is sitting in the seat (from this signal) it will fire the passenger airbag when the situation so demands. It won't fire if the signal says 'No one in passenger seat' (there can be a child or an 'underweight' adult in this condition).

In other countries, the driver and sole occupant of the car may need to carry a child in a child seat in a rear-facing position (forbidden to put it in front-facing position) in the passenger seat. In cars without weight-sensing seats, the passenger airbag will fire. To prevent this when carrying a child in the front seat, there is a switch that conveys to the ECU not to fire the airbag.

If your Airbag system is giving a warning, get it checked. Possibly there is an error associated with the weight sensor (wire loose or sensor kaput).

Last edited by DerAlte : 16th November 2015 at 15:31.
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Old 16th November 2015, 20:51   #11
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Default Re: seat belt warning, how..?

Quote:
Originally Posted by zipzapzoom View Post
Thanks for info guys,
so technically speaking, if one puts some heavy weight on the passenger seat, the sensor will get activated and the warning will come on. right??
regards
This might depend on the car, I think. The Nissan Sentra in my experience had this quirk of beeping the seatbelt alarm if I left my backpack on the co-driver seat, forcing me to keep it on the rear seat or the floor. IIRC, all other cars I have driven didn't show a warning or sound the seatbelt alarm in such a scenario.

Quote:
Originally Posted by Gannu_1 View Post
If it's just an audible warning through a buzzer that you need, you can get it done by replacing the seatbelt anchor that comes with the normally-closed switch. Connect it to a 12 V supply from the fusebox that turns on with the ignition and a 12 V buzzer, you're done. Once you holster the seatbelt, the switch is open and this disables the buzzer.

The weight sensor is usually provided for the co-driver seat.
This seems very doable. Thanks! I managed to find such a seatbelt anchor on Aliexpress, I'm sure car spare shops might stock these as well.

I tried looking but couldn't locate a weight sensor for the co-driver seat. I suppose the co-driver seat would have to do without the alarm in that case? Still, something is better than nothing.
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Old 17th November 2015, 09:08   #12
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Default Re: seat belt warning, how..?

Quote:
Originally Posted by Tanmay K View Post
I suppose the co-driver seat would have to do without the alarm in that case? Still, something is better than nothing.
Here's the wiring diagram for the Polo used abroad:

seat belt warning, how..?-bduknk6.png

You can see the driver side seatbelt warning is activated by the contact switch (E24) on the seatbelt anchor whereas on the co-driver side, it passes through the seat occupancy sensor (G128) as well.
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