Got a low tire warning today and it kept going down.
Had to cancel lunch with friends and head home before it went below 30psi.
(No MB dealer within 35 miles for nitrogen fill)
The pressure went from 36psi to 32 then back up to 33.
(The tire pressures have been rock steady since I bought this car 15 months ago)
Stopped and looked for a nail or a cut in the tire, nothing.
Measured the pressure to 35 in my garage when back in my garage.
Looks like the sensor was bad.
Is this common? How much for a new sensor and installation at the MB dealer?



Bought a spare tire kit, hate the helpless feeling of not being able to change a tire or have to wait 2 hours for a tow truck, then get an Uber home.

 

Air is 78% nitrogen. Get you own small air compressor or stop by a local gas station or tire shop to add air. No need to drive 35 miles to a dealer.

 

I agree!

People do not know or believe that air is 78% nitrogen.

Any competent tire dealer can replace the sensor for a fraction of the cost of bringing it to the dealer - unless your car is still under warranty.

 

You can confirm or dismiss sensor issues wherever you park with one of these, kept in every car I've ever owned. MB even provides several places where these can be clipped (glove box, console cover, etc). You might think these are for ink pens, but not necessarily...

 

How did the front left look compared to the other tyres when back at home? I'm after the pressure change from tyre temperature changes.

 

Or this:

 

they work with batteries right ? maybe one is almost empty ..?

 

Don't know how people still fall for the nitrogen scam. The only advantage that pure nitrogen has over the 78% in regular air is that nitrogen is an inert gas, meaning it doesn't absorb moisture. The biggest issue and why race cars use pure nitrogen is the moisture in the air that results in unpredictable tire pressure increases once the moisture turns into steam. Race teams need to be able to exactly predict the tire pressure at any temperature. That's not something that's even remotely of concern in a regular E Class. One additional advantage is that nitrogen molecules are larger than oxygen molecules, so they are less likely to escape through the pores of the tire compound, so natural loss of pressure is lower, but with regularly checking your air pressure and topping off with a simple compressor or even a floor bike pump is all it takes. Nitrogen still expands and contracts with temperature changes, so in the winter your pressure will be lower and higher in the summer even with pure nitrogen and you have to adjust it. Every 10F is about a 1 psi change in pressure even with pure nitrogen.

As for the TPMS sensors, first off what you see in the app are your hot pressures. Pressure increases as the tire heats up, and the app only shows the last pressure at the time the car was turned off. Tire pressure needs to be checked with cold tires. The sensors themselves are not the most accurate. They only have a 1 psi resolution. One of mine is consistently showing lower than actual and the other three are showing higher than actual. They are a piece of mind, but not to fully rely on and they can go bad. The battery will also run out eventually.

BTW, most shops that offer nitrogen fills produce the nitrogen on site, extracting it from the air (remember 78% in the air), and the equipment is often not the best. So what you think is pure nitrogen isn't actually pure in reality.

 

Here are MB part #s search should also pull aftermarket (kit contains 4 sensors if contemplating all one time). Check with local Discount Tire for install cost also check to see if they offer price match for same aftermarket sensor they offer found online. BTW they should also be to diagnose if sensor is malfunctioning.

 

I just use a tire inflator like this Ryobi, has been as cheap as $20-$25 when it's on sale. I have a bunch of other Ryobi tools too like their impact wrench which you could use for tire changes and those come with a battery and charger and the inflator is tool only. Also a couple PSI doesn't matter that much, I thought you were down to 20-25 or less. I get tires at Costco and they only charge about $20 or so to swap a rim and that includes swapping the sensor. But you have to have bought the tires there and if you're under warranty, have the dealer swap it. As it's only a few PSI, I wonder if you also checked for cracked or bent rims as mentioned earlier, those sensors aren't that accurate and driving will increase tire pressure along with warmer temperatures in a garage.

https://www.homedepot.com/p/RYOBI-ON...737D/307627867

https://www.homedepot.com/p/RYOBI-ON...62K1/317701837

 

I've never had a sensor battery go flat but if it did, the control unit should flag it with a fault message. Each measurement message from the sensor includes the sensor battery level info too.

 

Got my own compressor, but not in the car, back home in the garage instead, not much help on I-95 thirty miles from my garage.
My bad, should have bought the spare kit earlier.
We sure looked for a local tire shop, or service station, in case the tire was losing pressure. No idea if it was false alarm or really going flat.
(Driving 35 miles to the MB dealer was never an option. We were visiting St. Augustine when the tire pressure warning came on. A quick search for the
nearest MB dealer was disappointing, Jacksonville, 35 miles away)
Guess I should have worded my posting different, my bad.
Thanks to the posters with helpful comments.
​​​​​​​

 

After being stranded with a shredded run flat, I bought a spare tire and tools for my car. I also have a 12v/120v compressor on board. The peace of mind is worth every penny I spent. I need at least 1 tire repair every year (usually for a slow leak).

 

I have one of these cordless compressor in the trunk of my car..it has a digital pressure display which act as a pressure gauge and it also has a auto stop to preset. I usually charge it up once a year, one charge can pump 15 to 20 tires depending on the size of the tire.

 

Got a link or a picture of your cordless compressor?

 

Glad I went home and cancelled my appointments the other day:
Today the tire was Flat, as flat as a Run Flat can go..
I suspected a bad sensor or a bad battery in the sensor, but it was a good old fashioned flat.
Now I will see if the nearest tire place can patch it.
If not, ditch the Run Flats and get 4 regular Michelin Pilot Sport All Season 4 tires.
My local Discount Tire quoted $1,118.02 including a "Protection Certificate", taxes and everything else.
Asked my MB Dealer for their price for the same tires, waiting to hear back,
Pumping up the Run Flat, Flat in the garage, no Nitrogen.

 

. The simplest explanation is often the correct one. I caught two punctures so far thanks to TPMS displaying the tire pressures before even getting an alert. Both times I must have caught it the day before, and then next day as soon as the pressures displayed within a couple of blocks from my house noticed that one was much lower than the others. I pretty much always have the temperatures and tire pressures up in the instrument cluster on the right to assess the health of the car.

 

Norsey, Norsey, Norsey

 

I know, stubborn Norwegian here, don't hold it against me, but back in the old country I drove Mercedes Taxi cabs at age 20, been around cars, MB's and tires for a long time..
This was me in 1976, moved to the US five years later.

 

Well, 78% nitrogen!😎

 

Yes, always 78% N in ambient air.
Had no choice in this case, no N cylinder in my garage.
Been using N in aircraft tires for many years, but for a different reason than in cars.

 

Unless you track your car, you dont need nitrogen, it really cause more problems than benefits. TPMS, tire pressure monitoring systems, are not always 100% reliable, always have a tire gauge and compressor on hand, especially if you have runflats. I usually have a can of fix a flat and a tire plug kit in the trunk as well. Since you bought a spare, you would not need the plug kit. Not sure if the W213 allow for extra tpms sensor in the spare tire. I would try to patch the tire, if it is not repairable, since you bought spare alreday, go with the conventional tires. Just out of curiosity, are you just going to put the spare on the trunk floor, it will use up some trunk spare. Adding more weight in the back will benefit the car’s front to rear weight distribution.

 

I will check with a tire store if the flat tire can be pathed, if it can, problem solved, run a few 1000 more miles.
If It can NOT be repaired I will buy 4 new Michelins, Regular tires, NOT Run Flat,

I plan to keep the spare in the garage while running around town: If I have a flat, wifey can get me the spare with jack, etc.
For road trips I plan on tossing the spare/tools in the trunk/back, just in case..
I like nitrogen in the tires as they don't leak, supposedly N has thicker air molecules:

Turns out the Run Flats on my Wagon are not True Run Flats...

 

Mercedes spec out softer runflats, if you carry a portable compressor, you can go much further than 50 miles with a nail in your tire. Having a spare tire in the garage is as good as a portable compressor or tire gauge in the garage.

 

Spare tire in the garage for short trips, spare in the trunk for longer trips.
(My grocery store and dog park is 2-3 miles away, no need to lug a spare and tools around all the time. I don't carry the life raft in my boat for a trip down the
canal, but crossing to the Bahamas I do.)