How da heck the system works?
Manual is sketchy, I found this topic that explains emergency messages https://mbworld.org/forums/e-class-w...noperable.html
But no world how the system is set.
I experienced that it works on 1 of my tires, but alarm come 1/4 mile from my garage. Would the tire be really flat, it would be ruin already.
Than the driver has no info about actual pressure.
I do have add-on TMPS that I bought in 1995 and it does display the actuall tire pressure with 3 levels of different alarms.
So I am pretty disappointed with MB 2008 technology

 

You get what you pay for. In this case, it's the low end line. I think on the more expensive models like the E63, it will give you pressure readings, not sure about the E550. The W212 might also give you the actual tire pressure also. But it was still sorta new in 2008.

What's your problem anyway? Mine has come on a few times, usually one tire has dropped a couple psi below a certain threshold and it gets triggered. What's your question anyway? The real point of it is to alert the driver when one of the tires is below a certain threshold.

 

So main question is what is the "certain threshold"
The manual says something about system resetting itself at each inflation, but that is very murky.
Other dilemma is what batteries we have? Do they last "lifetime" .. like 722.6 ATF ?
Bottom line is how do we know it works at all?
I just changed wheel from other W211 and nothing.

 

I've had it come on a few times, it doesn't take that much to trigger it, I think it's mainly a difference in pressure from before. Like I said, they're not lifetime batteries, it's designed so that you can't replace them, you have to replace the sensors in the rim. If it wasn't working, you'd get an error message. You can go through the menu and reset the system after filling it up with air.

I think someone did hack one open and replaced the lithium battery, but you wonder how long it'll last when you're going 70+ down the highway.

 

If you have a DAS, you can diagnose what the issue is exactly. The DAS will show individual tire sensor status and pressures.

Also if you want to know the pressure from each tire on the IC, I believe you need to set to ROW. Mine is ROW and I can see all the tire pressures.

 

I believe what you get displayed really depends on the year and the model. On the E55 you might have the individual tire pressure, the VIN decoder probably says that you have the high line of the tire pressure sensor, on the more basic E350/E320 you just get the low line which just gives you a warning when the pressures have changed but it doesn't actually tell you which tire is low.