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Tire Preesure Waning - Why?

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E-Class (W212) 2010 - 2016: E 350, E 550

Tire Preesure Waning - Why?

 
Old 03-03-2019, 09:29 PM
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Tire Preesure Waning - Why?

I have had to check my tire pressure once ... and then scrolled through the menus to reset .

Now 3 months later- I am getting the same warnings.

Is this to do about my leaky airmatic suspension system?
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Old 03-03-2019, 10:18 PM
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Originally Posted by ChrisB View Post
I have had to check my tire pressure once ... and then scrolled through the menus to reset .

Now 3 months later- I am getting the same warnings.

Is this to do about my leaky airmatic suspension system?
Less to do with airmatic suspension (nothing actually) and more to do with the cold weather. Cold weather means the air contracts in your tires, giving lower pressure readings. Put some air in the tires and the pressure will rise above the set warning threshhold.
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Old 03-03-2019, 10:50 PM
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Natural leaks and temperature changes can make the system sensitive.
What I do is inflating the tires to recommended pressure on low side on cold morning, reset the settings and than add 3-5 psi I like to have over recommendations.
This way my warning is not coming on till I am really low.
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Old 03-04-2019, 10:06 AM
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Tire pressure should be checked and filled when the car is "cold". That is, first thing in the morning and before it is driven. If the car is not garaged, make sure the entire car is in shadow because the sun on a tire will increase its pressure. Tire pressure is dependent on temperature and altitude and must be checked once a month to adjust for the seasonal temps (and don't forget the spare). Do it on the 1'st so you will remember. Improper pressure effects tire wear and gas mileage and if you see one reading that is really off compared to the others, you probably have a slow leak that needs to be checked at a tire store. Buy a tire pressure gauge and keep it in your car. If you don't have you own air pump at home (which is worth the $20 investment to get one that plugs into your car's lighter socket), write down the pressure before you drive to the nearest gas station and then use what you wrote to add the proper amount.

The TPMS system of the car is not exact. It is primarily a safety feature to prevent a blow-out. I have set my tires to the exact same pressure using a tire gauge and yet the TPMS shows variations of 1-2 pounds among the four tires.

I don't recommend adding more air than is specified. I've never done it and have never had a pressure alert since I check my pressure regularly. Adding 3-5 pounds will increase tire wear in the middle of the tire, give you a rougher ride, and slightly better gas mileage.
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Old 03-04-2019, 07:11 PM
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Originally Posted by ChrisB View Post
I have had to check my tire pressure once ... and then scrolled through the menus to reset .

Now 3 months later- I am getting the same warnings.

Is this to do about my leaky airmatic suspension system?
Has nothing to do with suspension system.

You are located in Canada so you do not have the system that shows the actual tire pressures?
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Old 03-04-2019, 10:38 PM
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No individual pressure displayed.

Last time I had these warnings the pressures were exactly the same tire to tire & the correct pressure.

It has been cold (for us) in Vancouver - so temperature may be playing a factor.

I will check pressures and reset. Adding air if necessary.

The system must be pretty sensitive.

Thanks for the advice.
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Old 03-05-2019, 10:14 AM
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Originally Posted by ChrisB View Post
No individual pressure displayed.

Last time I had these warnings the pressures were exactly the same tire to tire & the correct pressure.

It has been cold (for us) in Vancouver - so temperature may be playing a factor.

I will check pressures and reset. Adding air if necessary.

The system must be pretty sensitive.

Thanks for the advice.
The system you have is based on wheel speed sensors detecting increased wheel speed if tire goes low in pressure due to smaller contact radius to road. But if you get alarm when all pressures are the same then you could have a wheel speed sensor issue.

Did the system tell which tire was low or just said “Check Pressures”?

With cold weather all pressures go down so as long as the pressures remain within some tolerance from each other you should not get the warning. I don’t think the system you have knows the pressure level of the tires, just the difference in wheel speed between them so you could run dangerously low pressure in all tires without knowing it UNLESS MB built a temperature memory in it that sets the outside temperature when you do the RESET.

This would allow the system to monitor the outside temperature and compare to the temperature at last reset and then calculate estimated tire pressure for the current outside temperature and then give the warning if the calculated pressure is far enough below the last reset.

I would think if the system system did not single out a specific tire being low then it assumed all is low. You said the pressures were correct when you got the first warning but the reset prior to that could have been done during warmer outside temperature setting the alarm point higher.

Im not an expert
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Old 03-05-2019, 10:22 AM
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Originally Posted by ChrisB View Post
No individual pressure displayed.

Last time I had these warnings the pressures were exactly the same tire to tire & the correct pressure.

It has been cold (for us) in Vancouver - so temperature may be playing a factor.

I will check pressures and reset. Adding air if necessary.

The system must be pretty sensitive.

Thanks for the advice.
The system you have is based on wheel speed sensors detecting increased wheel speed if tire goes low in pressure due to smaller contact radius to road. But if you get alarm when all pressures are the same then you could have a wheel speed sensor issue.

Did the system tell which tire was low or just said “Check Pressures”?

With cold weather all pressures go down so as long as the pressures remain within some tolerance from each other you should not get the warning. I don’t think the system you have knows the pressure level of the tires, just the difference in wheel speed between them so you could run dangerously low pressure in all tires without knowing it UNLESS MB built a temperature memory in it that sets the outside temperature when you do the RESET.

This would allow the system to monitor the outside temperature and compare to the temperature at last reset and then calculate estimated tire pressure drop for the current outside temperature and then give the warning if the calculated pressure drop is big enough.

I would think if the system did not single out a specific tire being low then it assumed all is low. You said the pressures were correct when you got the first warning but the reset prior to that could have been done during warmer outside temperature, which set the alarm point higher.

I’m not an expert on this system, just trying to understand how it could work, i.e. you may not have a problem at all.
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Old 03-05-2019, 11:14 AM
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Enter your VIN into datacard decoders to find what exactly you have.
Assuming we are talking about 2011 model, they should have full pressure display.
It was 2006-2008 era when MB was using tire warning system without actual display.
The tire rotation-sensing systems were short lived and I did not hear about them in American models.
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Old 03-05-2019, 01:41 PM
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Originally Posted by kajtek1 View Post
Enter your VIN into datacard decoders to find what exactly you have.
Assuming we are talking about 2011 model, they should have full pressure display.
It was 2006-2008 era when MB was using tire warning system without actual display.
The tire rotation-sensing systems were short lived and I did not hear about them in American models.
Tire pressure readings are required only in U.S. Canada uses the speed sensor system.
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Old 03-05-2019, 06:27 PM
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If you add any air to your tires you need to reset the system and start over with a new baseline or the alarms will become more frequent. My system alarms twice per year, Spring and Winter.
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Old 03-05-2019, 07:02 PM
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Unless it is alarming low, just leave it alone until temperatures normalize. Tire pressures go up and down through out the winter.
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