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Hello...I bought a new 2018 Mazda 3 Touring hatch, 6sp manual, in early July 2018. As of 31 May 2019, I have 662 miles on the odometer. About 4 weeks ago, the passenger seat belt light began going off (chiming/flashing) with no one in the vehicle except myself in the driver's seat. I buckle my seat belt 100% of the time before putting the vehicle in motion.

I had nothing sitting on the rear seat and only a wallet in a fanny pack and some other light stuff, probably weighing no more than 2 pounds max, if that, on the front passenger seat, which is normally what I place there. I live in mid-south Florida and am beginning to think the weather warming up may have something to do with this.

The passenger seat belt warning light doesn't begin going off until after I've driven the car for a few minutes/miles, and it's been sporadic. Sensor(s) going bad? Effected by hot temps? My car was assembled in Mexico if that makes any difference with the quality, which according to some opinions I've come across, it does, with Mexico built Mazda's <sometimes> being of lower quality than the ones built in Japan.

At any rate, this is my first Mazda and probably my last. Not impressed with it to date, coming out of an 18-year stretch of driving VW TDI Sportswagen manuals, which I had few problems with and absolutely no electrical/sensor related issues like the one I'm experiencing in the Mazda.

This coming week, I'm going to the Mazda dealer, where I bought the vehicle, to have it investigate the problem. On 30 May 2019, I shot a short GoPro video capturing the phenomenon as I was out driving to show to the dealer just in case the problem can't be replicated there. But any feedback beforehand from other Mazda 3 owners who have experienced this specific issue would be greatly appreciated.

I did try buckling the front passenger seat belt to see if the problem would go away, and it did. But that's not the long term solution I'm looking for. Nor do I want to start disabling sensors. Hopefully, the dealer will perform a fix that will permanently solve the issue.
 

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I've driven other cars where a light item placed on the front seat can trigger the load sensor. Don't put anything on the seat and see what happens.
 

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It's funny...if I plug my phone in to charge and set it on the passenger seat, the passenger seatbelt light and chime go off. If the phone is not plugged in, it doesn't.
 

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Hello...I bought a new 2018 Mazda 3 Touring hatch, 6sp manual, in early July 2018. As of 31 May 2019, I have 662 miles on the odometer. About 4 weeks ago, the passenger seat belt light began going off (chiming/flashing) with no one in the vehicle except myself in the driver's seat. I buckle my seat belt 100% of the time before putting the vehicle in motion.

I had nothing sitting on the rear seat and only a wallet in a fanny pack and some other light stuff, probably weighing no more than 2 pounds max, if that, on the front passenger seat, which is normally what I place there. I live in mid-south Florida and am beginning to think the weather warming up may have something to do with this.

The passenger seat belt warning light doesn't begin going off until after I've driven the car for a few minutes/miles, and it's been sporadic. Sensor(s) going bad? Effected by hot temps? My car was assembled in Mexico if that makes any difference with the quality, which according to some opinions I've come across, it does, with Mexico built Mazda's <sometimes> being of lower quality than the ones built in Japan.

At any rate, this is my first Mazda and probably my last. Not impressed with it to date, coming out of an 18-year stretch of driving VW TDI Sportswagen manuals, which I had few problems with and absolutely no electrical/sensor related issues like the one I'm experiencing in the Mazda.

This coming week, I'm going to the Mazda dealer, where I bought the vehicle, to have it investigate the problem. On 30 May 2019, I shot a short GoPro video capturing the phenomenon as I was out driving to show to the dealer just in case the problem can't be replicated there. But any feedback beforehand from other Mazda 3 owners who have experienced this specific issue would be greatly appreciated.

I did try buckling the front passenger seat belt to see if the problem would go away, and it did. But that's not the long term solution I'm looking for. Nor do I want to start disabling sensors. Hopefully, the dealer will perform a fix that will permanently solve the issue.
Did you happen to take it to the dealer. What did they do to resolve it?

My passenger lights came on too with something light (hot dog from Costco) on the passenger seat. I don't think it was interested in my food.
 

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Same here... just started doing it in the last month or so. I have 3 cell phones and it does it when they are in the seat.... however, when I have my backpack on the seat... EVERY MORNING... on the way to work (1 hour) it does not chime. So.... my pack weighs a couple of pounds... I put the phones on top of it with my lunchbox etc... no chime. I place the cell phones on the seat and it chimes. Electrical sensing from the phones? hmmmm.... hardly worth getting rid of the car for though.
 

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Unfortunately I'm too new to post links but if you Google for "CT-L1003_SRS.pdf" the first result has some interesting stuff. Page 64 (02-50) starts talking about the PODS / Passenger Occupancy Detection System. It includes some neat diagrams on how the systems in the passenger seat work.

On page 65 (02-51):
Furthermore, the occupancy sensor is able to detect a child restraint seat with transponders. Therefore, it generates an electric field using the sending antenna. In case a Mazda child restraint seat with integrated transponders is used, the transponders are excited by the electric field so that they impose a code on the sending field by means of modulation. This electric field is detected via the two receiving antennas and evaluated by the control module.
Sounds like a Hall effect sensor although I'm not an expert on that. And then on page 66 (02-52) there's:

NOTE: Metal parts or magnetic cards must not be positioned on the seat, as they might cause unintentional activation/deactivation of the passenger airbag system, resulting in serious injury or death in case of an accident.
That sounds a lot like what's being reported in this thread. A cell phone on the passenger seat must be influencing the electric field mentioned on page 55 causing the passenger airbag system to arm.

The PDF is from 2005 but I'd bet the system still operates fairly similarly.
 

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+1 for cell phone triggering it. My 2017 Sport triggers the warning with my phone but heavier objects don't affect it. Not sure if it's NFC(mine is always on), the magnet in the phone, or as someone else mentioned, some field generated when the battery is charging. Either way, i just know to keep the phone in the dash cubby or cup holder and I don't have issues.
 

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Without thinking about this thread to which I contributed several days ago, I noted that yesterday my passenger seatbelt/airbag light did not make any noise and I had at least 30 lbs of backpack/clothes/extension cord etc... on it. Looks like the cell phone electrical field trips the sensor, not just weight. Interesting.
 

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2017 Mazda 3 GT Hatch w/ Premium Package, Machine Grey Metallic
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I'm late to the party, but my 2017 Mazda3 GT has the same problem, except it is going off with only the metal end of an iPhone lightning cord touching the leather seat, phone in a separate cupholder. Also, my KN95 mask with the "metal nose forming part" of the mask was resting on the seat as well. This is the third time it has happened since I got the car in February, but I don't remember anything else on the seat the other two times it happened. My 2015 didn't have this problem with the fabric seats. Might need to make a separate post.
 
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