TPMS on E350 Question

[mbenz76]

I have the TPMS fitted to my E350 and although I rarely pay it much attention, I have been keeping a close eye on it over the last few days as I have lost a bit of pressure.

Mine shows pressure in bar rather than PSI. Whilst I know it is a relatively simple conversion, most airnlines in the UK seem kitted out for PSI and my mind works in PSI. Does anyone know if this can be changed? I can't find a setting for this anywhere.

Also, how accurate is it?

My tyre had a nail/screw in it about 2 months ago. It lost the head after a day or so if me discvering it and pressure never changed, so I didn't get the tyre looked at. Just done 500 motorway miles and discovered today that this particular tyre was down by 0.4 bar. I pumped it back up and checked it constantly and it hasn't moved again despite doing another 50 motorway miles afterwards, so I assume it was the heat of 500 motorway miles that caused air to escape.

I just wondered how accurate it was and whether it could be trusted as an indicator of true pressure.

 

[Xenon]

Well, my previous W212 had a tyre pressure monitor, and the readings would fluctuate quite a bit. I put it down to the temperature. However, it does beg a very important question. Do not rely on the readings alone?! I got in the habit of not checking the tyres (condition) and the pressures as I became lazy and considered that the monitor would inform me if they needed attention. Your nail story highlights this. Fortunately, I never suffered as a consequence, but it could have been a different story.

 

[developer]

I regularly set my tyres when cold via a gauge and pump and only use TPM to check things are ok as I'm driving.
Variations are common but I put that down to individual temperatures.

TPM only operates after the vehicle is moving and from my perspective, once moving, the tyres are no longer cold.

 

[mbenz76]

Just had it checked and it's a nail which is too close to the wall to repair, but since they are at 3mm and it's the rear tyres it's time to replace.

I have been told that the valves etc. are not part of the TMPS and that it uses the ESP to monitor them so Nyone can fit tyres and not worry about knackering the system if the valve breaks. Does anyone know if this is correct? I know my previous car (Renault) had TPMS but it was part of the valve assembly and most fitters broke them!

 

[npuk]

Mercedes use two different systems, which one you have depends on the model of the car.

The first is the direct system which gives you actual tyre pressures of each tyre, this system does have special valve and sensor. The sensors last about 5yrs before needing replacing. This is the system you have.

Valves dont really need changing unless your changing the sensor. Both can be purchased from: Alloy Wheels Direct Ltd | TPM Sensors | Tyre Pressure Monitor

The second is the indirect system, it does not give you actual pressures of each tyre, there is no special valve or sensor instead it uses the ABS wheel sensor to detect a loss in pressure.

 

[mbenz76]

MB tell me that the sytem in mine uses the ESP sensors to work it out and that tyre valves are bog standard.

This does raise the question about how they justify charging for the system if the sensors etc. are already there as part of ESP.

I have had to order 2 new tyres :-(. One is punctured beyond repair but both have 3mm left so it's about time I guess, especially as they are the drive wheels. More than a little annoyed that 15 months and 10k miles have eaten a pair of tyres to 3mm without thrashing

 

[Xenon]

Hmm.... I am certainly confused now! My previous late model 2010 W212 had the TPMS fitted and the Mercedes dealer told me to be sure to keep the value monitor cap when I had new tyres fitted! I believe there may be confusion here over TPMS and Tyre pressure loss monitor which does not require seperate value caps. Please enlighten......

 

[richard]

On the TPMS on my SL, the valve stems are aluminium, and if you put the standard MB metal dust caps on, they weld themselves on :-( so you must use plastic caps and MB have silver/grey plastic caps.

In my case the TMPS sensors are fixed onto the valves within the wheel. TPMS displays the pressures in the instrument cluster (and in the settings menu you can switch between BAR and PSI (to answer an earlier posters question). Some TPMS sensors (maybe not in Mercedes) fix on a band around the wheel in the tyre space of course !)

Tyre Pressure Loss warner is different and is just clever software in the ESP controller - it doesnt pickup all cases of pressure loss, so its just an additional safety help but never to be relied on. Its a very low cost option from around 2004 onward, and personally I think MB are cheeky to charge for a safety feature - but no doubt its development did cost MB a load of cash and thus that maybe why they charge. Easy enough to turn on if you know what you are doing in Star Diagnosis. I tend to enable it on cars that don't have it if I am doing any coding.

Richard

 

[mbenz76]

I purchased the Tyre Pressure Monitoring System as an optional extra so assume I have the better of the systems. My valve caps are cheap plastic (not sure about the stems).

They were quite adament that on my car it was not part of the valve system and used the ESP to detect the loss. To back this up when I get in the car it won't tell me the pressure until I have driven for a minute or so, but oddly will show an immediate change it I pump it up with the engine.

Looked through the menu on the car and can find no way to change from BAR to PSI

Got my new tyres sat in my kitchen and am having them fitted by the MB dealer in the morning. £188 each for 265/35/18 97Y Extra Load ContiSport3 if anyone's interested from Camskill online - best price I could find. MB fitting them for free

 

[whitenemesis]

Am I correct in thinking tyre pressure loss warning systems are now compulsory on new cars?

 

[st13phil]

Am I correct in thinking tyre pressure loss warning systems are now compulsory on new cars?

AFAIK it's compulsory only if the vehicle is fitted with runflat tyres, otherwise it's not.

The Tyre Pressure Loss warning system is standard equipment on the W204 & W212, while the Tyre Pressure Monitoring System (which provides a readout of tyre pressures on the instrument cluster) is a cost option.

 

[whitenemesis]

Just found this

"The European Commission decided that an inflation pressure monitoring system ( TPMS ) will be mandatory for all passenger cars launched after Nov. 2012, and for all cars firstly enter into service after Nov. 2014"

Trying to find the originating doc

 

[mbenz76]

If as I have been told the TPMS simply uses the EPS sensors which are already on the car, then how the hell can they justify charging such a premium for it?

 

[Xenon]

Good question. I spent £295 to have TPMS on my last W212.

 

[npuk]

Have a look at the alloy wheel once the old tyre is removed, I would say there will be a sensor attached to the valve as shown in the alloywheelsdirect link I posted. Cannot find any info at all on MB having a new system that gives pressures without any additional hardware i.e. valve or sensor.