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A few days ago I noticed that my TPMS warning light was on. It blinks when I first turn the car on and then goes to a steady on after a minute. This indicates that there is a bad sensor(s). Kind of bothered me that this happened so soon. I was hoping for a few more years. So I take the car to a national tire shop and ask them to tell me which wheel has the bad sensor. They test all four and say that they are all testing as bad. I find that pretty unlikely and plan to get a second opinion in the next day or so.

When I do find out which sensor(s) is bad, how easy is it to replace the unit as a DIY project? I've watched a few You Tube videos and it looks like it can be a DIY job. The tire store charges $60 each if they do it. I guess the other option is that small piece of black electrical tape that some people use. :) Have to ask if TPMS has to be working for a car to pass inspection in NC.

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
 

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It's not really a DIY project as it takes popping the tire bead on one side, and pushing the sidewall in enough to work on the tpms sensor / valve stem.
Most tire places pop both beads, work on the sensor, and then they have to reseal both sides, basically remount the tire, and re-balance.
$60 each isn't bad if you consider $25? of it is the normal price for mount and balance of just a tire with a rubber stem.

A decent tire shop points their scanner to each wheel and it shows right on the scanner the psi of that particular wheel.
But I've found that they have to select a YEAR and BRAND (car) first on their scanner menu so the scanner may not have the Smart in it...
 

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Discussion Starter #4
Yeah, the "kid" asked me about year, make and model and supposedly entered that info into his tester. He said he was receiving data, but I can't believe that all four sensors conked out at the same time. Hope to get a second opinion today.

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
 

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Discussion Starter #6
I did find out that the TPMS system does not have to be working to pass NC inspection. I'm eleven months from my next inspection, so I suppose I'll address it in some way by then. Second tire shop tells me $130 to replace a sensor!!! That's nuts!! I will go by there though to get a second reading. I don't see any way that all four go bad at once.

I'm close to needing two front tires on the coupe. I will likely get new sensors on them when that happens whether I need them or not. The warning light I am getting is on the cabriolet and it has new tires all the way around.

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
 

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MY08 cabrio MY09 cabrio Brabus MY15 ED
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Second tire shop tells me $130 to replace a sensor!!! That's nuts!!

The warning light I am getting is on the cabriolet and it has new tires all the way around.
$130, was he wearing a mask and pointing a gun?

Discount Tire charged me $50 - 60ish each to replace the sensors - unfortunately can’t argue that cost as there is a lot of labor required!

“New tires” on cabrio, recent replacements or original? If recent purchase might want to ask the installer to show a little love (discount)?
 

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Discussion Starter #8
The $130 was a phone call discussion. Owner mentioned that they would have to activate and sync sensor, but AFAIK that isn't necessary on the Smart's sensors. $130 is certainly way out of line. This shop has always treated me fairly, so I'll cut them some slack on that cost even though I won't be getting them done there. :)

And BTW, it was Discount Tire that told me about $60 yesterday.

New tires were bought online and installed locally, so even though they do provide lifetime balancing, they really don't owe me much. Just checked my tire installation receipts and the shop did install new sensors when they did the fronts about ten months ago. So that should rule out any problem there or if there is, then maybe they need to take some responsibility. Cost for the sensors for the fronts was $8.95. No such note on the rear tires installed in January.

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
 

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Batteries are sealed in. Life seems to vary, some going 10+ years, others lasting 5-6. They are motion activated, apparently, which makes sense. The standard units are Shrader 28214 model. Mercedes badge engineers them by putting the star emblem on them, and charging a shitload more.
 

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Discussion Starter #13
As MB DNA says, I bet I only got the rebuild kit and no new battery. Receipt lists them as "sensor kits."

So here's a thought I had - dangerous to be thinking, but how about this? Can I test my own sensors by say taking each tire down to about 20 psi one at a time and seeing if I get any low pressure warning?

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
 

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Batteries are sealed in. Life seems to vary, some going 10+ years, others lasting 5-6. They are motion activated, apparently, which makes sense. The standard units are Shrader 28214 model. Mercedes badge engineers them by putting the star emblem on them, and charging a shitload more.
When you say they are motion activated, does they mean they will last longer with less miles even over a longer time? My sensors are 11+ years old, but the car only has 5,200 miles on it.
 

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MY08 cabrio MY09 cabrio Brabus MY15 ED
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When you say they are motion activated, does they mean they will last longer with less miles even over a longer time?
Yes, but your sensors are on borrowed time my friend.

Your Garage Queen’s batteries will age out before the miles get them.

Problem is they go out one at a time and that usually causes you to replace them ALL out of frustration.
 

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As MB DNA says, I bet I only got the rebuild kit and no new battery. Receipt lists them as "sensor kits."

So here's a thought I had - dangerous to be thinking, but how about this? Can I test my own sensors by say taking each tire down to about 20 psi one at a time and seeing if I get any low pressure warning?

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
You pose an interesting question. The typical scenario is that all 4 sensors are working and one or more tires go low, triggering the TPMS reader. The owners manual does not specifically address what happens If one or more sensors fail, so the question is does it care if there is one or more low pressure signals, vs the absence of one or more signals, caused by a dead sensor? I suppose I could test it by putting one of my donut spares without a sensor on, pressing the reset button and going for a quick spin. All of my sensors are new. If the system is looking for 4 separate sensor signals and only sees 3, it should trigger. If it’s happy with seeing 3, it shouldn’t trigger. In that case, you should be able to identify good sensors by reducing air pressure in each tire one after the other. Lower pressure in a dead sensor tire wouldn’t have any effect. There’s a technical overview book on the Smart that I have in PDF format somewhere that may address the TPMS in more detail. I’ll look for it.
 

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25% air off manufacturer's recommendation and the tpms will trigger...
That makes sense for the sensors themselves. That in conjunction with this, from the manual:

“The TPMS must be restarted when you have adjusted the tire inflation pressure to a new level (e.g. because of different load or driving conditions). The TPMS is then recalibrated to the current tire inflation pressures.”

So essentially, the driver has to tell the system that the tires are inflated properly, and it uses those values as its baseline or reference values.
 

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A few days ago I noticed that my TPMS warning light was on. It blinks when I first turn the car on and then goes to a steady on after a minute. This indicates that there is a bad sensor(s). Kind of bothered me that this happened so soon. I was hoping for a few more years. So I take the car to a national tire shop and ask them to tell me which wheel has the bad sensor. They test all four and say that they are all testing as bad. I find that pretty unlikely and plan to get a second opinion in the next day or so.

When I do find out which sensor(s) is bad, how easy is it to replace the unit as a DIY project? I've watched a few You Tube videos and it looks like it can be a DIY job. The tire store charges $60 each if they do it. I guess the other option is that small piece of black electrical tape that some people use. :) Have to ask if TPMS has to be working for a car to pass inspection in NC.

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
Why don't you think a tire could be low? fill them all up to over 30 psi rest tpms light and see if light goes out then wait for it to come back on if there is a leak of some kind. I also have a 2014 and original tpms units are still working.
 

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Discussion Starter #20
First thing I did when the light came on was check the tire pressures. All were within about 2 psi of where I like them and would not have triggered the warning light. Then I read the manual and saw that the warning I was getting was not from low pressure, but from a bad sensor(s).

Len
2014 EV Coupe 20,000 miles
2014 EV Cabriolet 19,000 miles
 
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