jctevere

Hi all, I was just wondering if any of you happen to know if the TPMS sensors in our cars have a minimum PSI that the tires must have in them so that the sensors don't go off. I recently brought my car in for inspection service and they removed the wheels to inspect brakes. Later that day the TPMS sensor went off and I checked tire pressures, everything was fine. I went into the service system and reset the TPMS to use current values. The next day after I was driving it went off again.

I figured I would spend the day getting optimal tire pressures, and read that a few people liked 27.5 PSI for front and 31 PSI for rear. I made adjustments to my tire pressures to be exactly that, and went into to car system to again "reset to current values" But about 2-3 minutes late the TPMS sensor goes off again (and I check tires, same PSI as when I put in)... It is really starting to **** me off. That, and the fact that the TPMS sensor doesn't say which tire is tripping the system.

My Question Is This:
Is it possible that the dealership never reconnected the TPMS sensors in the wheel to the vehicle when they took the tires off? I looked and I didn't see any connectors? How does the TPMS in the tires connect to the vehicle?

Secondly, is it possible that 27.5 is too low for the TPMS sensors despite me setting that as the correct tire pressure?

Lastly, I have not yet checked for any nails in the tire (I don't think there are any as the tire pressure remains the same) but perhaps I am not losing air and it can detect if there is a foreign object that penetrated the tire? Any help here would be appreciated. Either way I am bringing in my vehicle to the dealership next week to replace weatherstripping and I will have them look at it then. But I would like to get this resolved ASAP as it is really annoying and if there is in fact a problem, I would want to replace it soon so I don't get a flat. Tomorrow I will look for any nails or something.

nyca

You can't reset the system to accept a tire pressure more then 3 PSI below what the rating on your door jamb sticker is - at least that is how my car works. So 30/35 means you can't go lower then 27/32.

RLE

Since your tires have not lost pressure, you can rule that out now.

All W204 models use the same sensors even though recommended pressures vary according to wheel and tire size.

TPMS sensors of the same brand can be installed with no problem and work the same as factory installed. Mine came from Tirerack for my winter wheels.

The sensors are not wheel-specific (like some other MB models) and they communicate wirelessly with the unit in the trunk. They contain a battery which supposedly has a ten year life. Hmmm, just like a Prius. If a tire is dismounted, it's possible to damage a sensor which might cause an alert and something similar happened to my car, done by the dealer.

I have never heard of a minimum pressure level for sensing and don't believe it. The official MB explanation to me was that once the system is set, it takes a 5 psi drop to turn on the light.

Since you don't have a tire problem, let the dealer sort it out under warranty.

Azn_C300

BTW, plugged into a STAR diagnostic system can detect which tire was throwing the error. Each sensor has a unique serial number. There's also a history of pressure checks that your vehicle computer stores and at what mileage the last reading was taken and stored.

JimPap

If you've had a tire replacement (same rim, new tire) its more likely that they've broken the TPMS sensor.

This happened to me a few months ago and they had to go get a replacement sensor. Was at the tire shop for 3 hours that day. aaargh.

jctevere

Thanks for the feedback guys, I looked at all my tires today, and no nails or anything that I could see that could be causing the error. I guess it will just have to wait until I bring it in to the dealership in a week. These are the stock tires with 15k miles on them, nothing was wrong until they took off the rims and tires off the car to check brakes. I dunno if its a coincidence or what. Thanks for the info on Star diagnostic system AZN, I just wish the car wouldn't treat me like such a brainless moron, at least my cadillac escalade says which tire is low, and even gives a readout of each PSI in each tire all the time...

On a side note, after I reset the car TPMS caution to Set current values and default values, about 2 minutes later the car screen says "correct tire pressure" (in the non-important white information screen)

I have no idea what that means, but it is shortly followed by a tire pressure warning within 2 more minutes with the red info screen. I dunno if that is normal or if it helps or not.

nyca

When you inflate the tires to the PSI level on the door jamb, and reset the TPMS system - what happens?

JimPap

jctevere,

Just to cover all bases, you are resetting them while driving at a constant speed, right?

dcjwlee

I think the blue background message goes off at one threshold and the red one after some more air leaks. Why your car progresses through the two when there is no air leaking is beyond me.

Probably a broken TPMS sensor. Not uncommon across all brands of cars.

I had a slow leak that MBZ couldn't diagnose and I'd lose 5 psi over the course of a week. That's not the case here, so this should be a pretty easy diagnosis once you get it in.

JimPap

You've got to be kidding.

Did you ever have a tire patched? I did and I still lost air from around the patch. The tire shop did the patch wrong and basically ruined a tire.

dcjwlee

No, it wasn't a patched tire. That's frustrating as well, but I forked over almost $1000 for the wheel and tire protection package at purchase and they just would not take my word for it and could not "diagnose" it.

Finally, it got to the point where the tire would deflate OVERNIGHT. Now let's just say the first morning this happened I was extremely unhappy to spend 3 hours in the dealership (go figure, all the SA's were on lunch break and they won't let me see the SM to explain what was obvious...)

Well, they sure "found" the leak that time. I got a tire replaced under the insurance package and went home. Next morning, I wake up prepared to make up for lost time and go figure... tire deflated AGAIN.

I tried to take off the wheel, but god knows how tight they torqued those bolts I couldn't get them off for the life of me! (i'm not a small guy either.... 6 foot hair under 180lbs.) and stomping on the damn wrench wouldn't even do it. Had to fill the tire several times on my way to the dealer because there was NO way I was waiting for a tow truck.

Luckily, that time I got a loaner and left. Final diagnosis was a cracked rim that the dealer had already diagnosed as "bent" but would not honor the tire/wheel package because it wasn't losing air. They fixed it right thatlast time....

BEEPbeepZIPtang

'

INTERESTING...Haven't changed anything recently (running aftermarket 19's with OEM TPMS sensors). Within the last week to 10 days, for no reason, I've been getting the "correct tire pressure" msg. So I checked the PSI and they are all spot on. It's funny because that msg is sort of ambiguous. I'm not sure if it's telling me to correct the tire pressure or it IS the correct tire pressure. anyways...

I think its electrical and not related to bad TPMS's because this happened the exact same time I blew a head light. With in that 24 hour period the sunroof started sputtering (it would/will only open and close at short intermittent bursts, maybe an inch at a time).

The car is an 08 with 28K on it. I bought it new and have not had a single problem (other than the gas gauge getting stuck at about 6K) so I find it odd that these 3, completely separate, other than being electrical, systems are all failing at the same time...without it being related. It's gotta be.

lfilomeno

I also haven't changed anything recently but as you, within the last week for no reason, I've been getting the "correct tire pressure" msg. I have a service appointment tomorrow so once they figure out what is the issue, I will post the results here.

Mark1605

I've had a silimar problem with our 2009 c300. My wife was driving it two days ago when the speedometer display changed to red and a message to check tire pressure came on. She got the car home and I checked the tire pressure in all four tires and they were right where they should be. Started the engine and drove it around the block. Red warning light was not on, but the little light on the display showing a "tire" was on. Reset the tire sensors to "current values" and the light went out. So far it has not come back on and no more red warning light in the speedometer display. Got a feeling this isn't the last time I'll have this problem; if it happens again I'll have the dealer repair it. Car is still under warranty.

Sportstick

I can envision one possible scenario to explain this...weather.com shows your temperature today was in the 50s, probably cooler than last time your tires were checked, so you may be close to the pressure spec. So, Charles' Law suggests when she came out to her parked car with cooled off tires, the pressure was below the setting. By the time she drove home, they warmed up and expanded, ready for you to find them at the seemingly proper setting. I suggest a tire gauge reading on cold tires first thing in the morning as we get into winter temps, remembering that 10 degrees F drop equals about a loss of 1 PSI. Get them set for your ambient temps, and then watch for any red cluster warnings.

JimPap

Sportstick,

Is that 10 or 20 degrees equals about 1 PSI????

Sportstick

10 degrees F equals 1 PSI according to my tech.

RLE

Wrong. You really ought to reset the system before driving in the morning so that the tires are cold and you know the pressures are equal and correct.

There are too many threads on this same subject.

Glyn M Ruck

Plug the thing into a Star - find out which sensor is screwing around. Make Benz replace it.

Peabody

I think it bears repeating that you need to reset the TPMS (and check air pressure) while the tires are cold. If you drive them over 1/2 a mile you may need to overcompensate as much as 3 PSI, which coincidentally is how much pressure drop will trigger a TPMS sensor. People who drive them to the dealership and then check the tire pressure, and find that their pressure is spot on are probably under-inflated.

RLE

As I posted just yesterday.

I had an incident of pressure loss a few weeks ago which I originally thought must be a nail but turned out to be sudden slow air leakage around the valve stem. Tightening the fixing nut a small amount eliminated the leak. That o-ring (German rubber and it's inside) at the base of the valve stem had compressed a little in three years to allow a little air to sneak past.

The tire was down six pounds from where I had inflated it previously (33psi) which verifies the five pound drop alarm threshold.

430752

That's my guess at least. A couple of weeks ago my tpms came on. I thought it was the sudden change in weather (got a lot colder, quickly). So, I filled the tires up and reset. Two weeks later, again. I had this problem last spring (but not when temps changed or anything). And 6 months after I bought the car too. Others report seeming gremlins in the tpms. Of course, it would help if mercedes reported which wheel, like my wife's 5 yr. old honda does. Or even the pressure values like current econoboxes do.

But of course, this is the car company which used lug nuts on my car which are now rusty after only 3 winters in NJ. Yeah, rusty. I've had 15 year old saabs and 10+ yr. old subies, and even a 7 yr. old chevy that never had rusty lug nuts. Of course, I'm out of warranty. Not a big deal to replace, but all four wheels? rusty? Kia makes better cars than these.

AkaSigFreak

When I changed my rims, I asked the tire tech about a TPMS rebuild kit. He told me they would be fine without it. I had repeated problems similar to your experience. I was then told that the O-ring begins to dry-rott over time and that is why the rebuild kit is recommended. They reinstalled with the kit and no problems since.

Glyn M Ruck

+1

omgitselaine

Funny it seems as if every change in season ( usually Fall ) a lot of us have these TPMS issues because of the temperatures lowering and we all get that dreaded Red Warning light The one time i drove the C last week guess what came on ..... yep that light UUGGGHHHhhh !!!!!!