lsbrodsky

09 E350 USA version. I did a search of all TPMS threads and there is plenty of conflicting information. My wife's car had the "check tire pressure" message when the car was shutdown. I read the manual, checked pressures, reset the TPMS, and all is good so far. I am a bit puzzled because it did not seem like any of the pressures were out of spec. But for any of the experts I have the following questions:
1. Does this TPMS truly have active pressure sensors on each tire? Spare tire, too?
2. What are the specs for pressure difference between tires or low air pressure that will trigger that warning but no dashboard lights or warnings?
3. Why is there a warning in the manual that a catastrophic pressure loss will not be alarmed by the TPMS?
4. Finally, why is it necessary to drive the car some distance after resetting the TPMS for the warning to disappear?

Larry

lkchris

You can tell by the funny looking air valves on the tires, not spare. Do not install metal caps.

There's a mimimum that will set off the warning, but before that there's a percentage drop from the desired pressure, which is what it was at last reset.

A catastropic occurrence is instantaneous and a warning is superfluous. You don't really need a dashboard warning that you've had a blowout. In addition a blowout might kill the sensor.

The sensors are rotating with the wheels, as they're attached to the air valve--could be radio transmission from sensor to receiver happens best when closest. Also, the system probably self-checks by taking a few readings first before storing info.

lsbrodsky

Thanks Kent. I don't know what kind of valve caps came from the factory as there were metallic N2 fill caps on the car when I picked it up from the dealer. I am not a N2 fan and I replaced the caps with metallic Mercedes logo caps. That has not seemed to affect the system as it warned me properly. I just saw in some posts some opinions that the US version used ABS sensors and rotational speeds, but others thought pressure sensors. Since the US version cannot read out individual tire pressures, I have no way of knowing for sure.
Larry

Barry45RPM

TPMS equipped cars come from the Factory with plastic valve stem caps spray painted gray. Non TPMS cars come with basic metal caps.

lkchris

The ABS stuff was on very early models and is no longer seen on new cars.

You can identify the pressure sensor air valves, as there's a nut securing them to the wheel.

LeviDenim

I am confused. I have the TPMS and I get readouts for all four corners on the display.
Mine is the Beru based system and works like a champ.
So why does Isbrodsky saying that the US models can't display individual pressures?
Also I have the metal stems with the nut that secures them to the wheel.

konigstiger

For your MY05 TPMS was an individual cost option able to display individual tire pressures, Larry’s USA MY09 TPM warns of inflation loss in one or more tires but does not display tire pressures.

konigstiger

FWIW EPC shows for MY09 each wheel is equipped with same sensor used before (able to monitor both pressure & temperature) and control unit but MBUSA eliminated the four antennas to wheel housings and replaced with one front central antenna no longer allowing for individual tire monitoring. I believe if stored pressure falls below 5.8 psi, a warning is displayed. I am assuming your problem “may” have been temperature rather than pressure

lsbrodsky

konigstiger,

I don't understand. What would be the purpose of monitoring temperature in the tire if you are also monitoring pressure? I mean you want the pressure in a narrow band for safety and ride comfort, but temperature can vary from very low to high due to ambient? Thanks
Larry

amdeutsch

Because there is a relationship between temperature and pressure. Thats why you want to adjust pressure before you drive. A rolling tire will heat up and the pressure will increase; its thermodynamics.

lsbrodsky

Yes, there is a relationship between pressure and temp but the tire is at 28-33 psi. Consequently pressure may increase around 4 pounds from cold to hot but temperature can start at ambient of below freezing and increase to 90-100 degrees F. That is why I cannot understand how temp monitoring on a tire can tell you anything useful. What I would really like to know are any alarm setpoints on the TPMS.

Larry

LeviDenim

We have a horse farm so I always have nitrogen here for welding. I have been using it for
all the cars.
The benefits seem to be worth it especially when I just have it sitting here. At least 30%
less pressure change due to temperature and the one I really love is that 99% of moisture
in the tire is gone. Air filled tires can and will end up with water in them over time.