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I admit I am paranoid about cracking rims on our potholed roads here, so I may be a little oversensitive to TPMS warnings. But I can't figure out why I get them sometimes.
Last year my wife hit a bump. It immediately triggered a warning on that wheel. It wouldn't go away until I "retrained" the system.
Today she got another warning, on the right rear. Yellow on the TPMS screen, and the yellow idiot light. She did NOT hit a bump or anything. Checking the pressures, they were the same as they were the day before. After driving a little bit, the right rear one went out, but then immediately right front came on. By the time she got home and I got to look at it, boht the right rear ad right front were on, but the pressures were both 34 psi which is fine. The two tires on the left were both 35. Again I just reset the values and everything cleared up.
Two weeks ago I had taken a bit of air out of the tires once the big cold snap went away. I set all 4 to 35, and reset the system.
What is triggering these warnings on the TPMS? I've never seen anything like this on any of my other cars. Sure, when I have a leaking tire, or just on a particularly cold day when the pressures are actually lower, they go off. But not randomly, with no loss of air.
And why could I have had cars 12 years ago where I didn't need to "tell" the system what the correct pressure should be by resetting it, and why did those same cars from the very early 2000s also not need me to drive around the block four times to see my tire pressures? They just worked. All the time. Even without the engine running (which MB seems to need).
I hope you vented off?
When you get the warning, what did the pressure display say?
I had warning coming on me couple of times, when pressure dropped from 38 to 36 psi and the system show precisely where and what it is.
Bare in mind that when you inflate 35 psi and set TPMS on warm day, few days later on cold morning or cold night the pressure will drop to 33 psi and possible trigger alarm.
The motion-activated sensors are for battery saving. My Ford truck shows tire pressure in just seconds, but big wheels do have bigger sensors and I hope bigger batteries.
Would hate to have batteries going bad after 3 years, when tires have more than 50% of thread.
My wife said this time around it was at 31. As I recall when I de-flated a couple pounds last week, it was 33 or 34 when I reset the system values.
What is the criteria for triggering the alarm? Every other car I had it was 30 psi. If the tire got below 30 you got a warning, but if it went back up on its' own it went away. This system is so weird. Isn't it a liability to have drivers arbitrarily just resetting the system to get the light to go out (I'm picturing unscrupulous sellers) while their tires slowly go flat under them? And how much of a pressure drop triggers the alarm? In this case I had the system set for 33 or 34 and it went down to 31. That, to me, is fine. Is it only 2-3 psi? Because normal weather fluctuations can just set that off. For every 10 degrees of temperature change your tires gain or lose 1 psi. Plus, doesn't the system reset on its' own when the pressure goes back up? I took the car with it alarmed at 34. Before I reset it, it got up to 35/36 and still yellow with an idiot light. That should be MORE than enough pressure for the system to be satisfied, no?
This is all happening on your 2014? I don't have any issues with the TPMS going off on either sets of wheels(summer and winter set) for my 2014. We have had some extreme weather here in Chicago with fluctuating temps and I have not had any warnings at all. Maybe you have some additional problems that lie in the receivers or beyond the wheel sensors themselves. I'm not sure how one goes about diagnosing that.
Did not study manual (sometimes it is good idea) but 2 psi trigger WARNING on my car, so 2 or 3 drop on yours sounds like the system is doing its job.
Again, it is you who can reset the system. The best way is to inflate your tires one afternoon while giving them couple psi more, than next morning bring the tires to perfect level and reset TPMS.
This way the tire pressure can be only higher with temperature changes than what TPMS remember.
Why?
Just keep the pressure at correct level. I have 1 tire with miniature leak, that needs air once a month. To avoid hassle, I reset the TPMS in the morning and then added 3 more psi, so I have 5 psi margin error before the warning will come.
All I have to do is display the pressure every couple of weeks. Even pressure will change during driving, comparing the leaky wheel to the one on other side, I know where I stand.
But that's exactly my point. If a 2 psi change triggers the alarm that's too sensitive. I'm not going to go find a gas station and adjust my pressures every time my tires warm up. Tuesday morning it was 9 degrees here, yesterday it was 48. That's a 4 psi swing right there without ever having had to take the car out of the garage. Couple that with the fact that my wife works 135 miles south of my home...you see where I'm going.
Sure, I could just de-flate all my tires to whatever the minimum safe limit might be (say, 28 psi or something), reset the system, then re-inflate them back up to 34-36 where they should be. But then, even if I do get a leak or a REALLY cold snap, the system doesn't reset itself on its' own. At least, mine doesn't. So even though my tires are just fine, I now need to go again to de-flate, reset, then reinflate, just to get the light to go out?
I'm sorry, that's ridiculous. I can guarantee you I am more hands-on, engaged with my cars than 95% of the MB owners out there and I don't feel like I should need to go through that. You mean to tell me all the elderly lady MB owners out there are running to the dealer every time a light comes on the dash just to get their tire pressures adjusted?
Point #2 is that it's just unsafe. Humans have proven time and time again that they are idiots. You know what a safe pressure is for your tires. I know what a safe pressure is. Most of the people on this board also probably know. However, 90% of the people who buy these cars do NOT know, and if you were to ask random people on the street what the tire pressures on their car should be, none of them will know. Because they have been conditioned to be ignorant, coddled pansies, and rely on a flashing light on their dashboard to determine what those pressures should be. So, how is it that MB considers it OK to just let ignorant Joe Owner re-train his system to make the lights and messages go away, and drive around with all four tires at 14 psi? "But hey, my car told me it's OK so I must be good!"
Sorry, every other car manufacturer had this figured out back in 2004. Catch up, MB. The warning goes off at 30 psi. Period, full stop. Below 30, warning. Above 30, warning goes away.
Or, which was the original intent of my post, is there something going on with my system?
Once again, I don't have any of these issues you describe with my TPMS system on two different wheel setups. I seriously think you have something else going on.
Perhaps. Wish I knew where to begin troubleshooting it.
Car's in right now getting new tires. I'll actually be happy if they find a leak, at least there will be SOME issue I can work against. But, I'm really not losing pressure other than what I consider normal temperature fluctuations.
My daughters Honda Fit kept throwing the TPMS warning and we finally found a screw in her rear tire. Unfortunately the system in her car does not show individual pressures, so it took us a while to sort out the issue and find the problem. It was a very slow leak and not obvious for quite some time. Good luck sorting this!
IIRC by law (TREAD Act), all TPMS tire systems must give a warning at or before 25% of the set reference value is lost (i.e. the current tire pressure is at least 75% of the set value). Some cars do not let you set the reference value. We have an older Honda where you cannot reset the system or set the values base your preferred tire pressure. The door placard on that car recommends 32psi and the warning light comes on at about 25-26 psi (almost 25% loss in pressure).
In my W212 (which we all know let's you set a reference value), I have noticed that it gives a 'soft warning' when you get about 10% low. In my car that soft warning is a 'check tire pressure' pop up on the center cluster and shows the current values. I consider this a soft warning since it can be dismissed with the OK button. When the loss is closer to 20-25% the pop up turns red and I don't think I could dismiss it (it's been a while so I can't say for sure). I consider this the hard warning.
Keep in mind that MB could have programmed in a minimum tire pressure for warning purposes. Considering we can set the reference value, it would seem unsafe to let someone reset the reference values when the tires are so low that driving on them could be dangerous. I don't know if MB actually has a minimum, but they could have a fail safe built in.
IIRC by law (TREAD Act), all TPMS tire systems must give a warning at or before 25% of the set reference value is lost (i.e. the current tire pressure is at least 75% of the set value). Some cars do not let you set the reference value. We have an older Honda where you cannot reset the system or set the values base your preferred tire pressure. The door placard on that car recommends 32psi and the warning light comes on at about 25-26 psi (almost 25% loss in pressure).
In my W212 (which we all know let's you set a reference value), I have noticed that it gives a 'soft warning' when you get about 10% low. In my car that soft warning is a 'check tire pressure' pop up on the center cluster and shows the current values. I consider this a soft warning since it can be dismissed with the OK button. When the loss is closer to 20-25% the pop up turns red and I don't think I could dismiss it (it's been a while so I can't say for sure). I consider this the hard warning.
Keep in mind that MB could have programmed in a minimum tire pressure for warning purposes. Considering we can set the reference value, it would seem unsafe to let someone reset the reference values when the tires are so low that driving on them could be dangerous. I don't know if MB actually has a minimum, but they could have a fail safe built in.
Agreed, and that is the same on my 2014 E350. I have changed wheels and currently have three sets, one for the winter, one for summer, and one that is impractical. On all of them I installed MB TPMS and had them link up with the car automatically. However, they did not work perfectly every time. It turned out that on two occasions, one TPMS had a bad/low battery and one had a bad transmitter. After replacing the afflicted sensors, the entire system worked fine with the soft warning/hard warning progression. Once I had a leak, the soft warning came on, then after more air escaped, the red warning flashed -- by that time I was at the tire shop and replaced the tire. I have never had the system issue a warning for the 3-4 psi fluxuations that I experience here in NY on a regular basis (since all 4 tires experience the same or a similar temperature variation). The TPMS warning usually only comes on if the psi in one or two tires is significantly different from the others (my guess, 6-10 psi variation). So, I think you have a problem with one or more of your sensors. If the ones you have are original to your car, the batteries in each are only supposed to last about 4 yrs, more or less depending upon use (remember, the TPMS batteries drain any time the car is on, whether the car is moving or not).
Thanks guys. Thefisch this is the explanation I was looking for. I've never gotten to that "red alert" stage. Came back from the tire shop at about 38-40 psi so I doubt they'll be going off anytime soon. It's supposed to get into the teens over the weekend then back up to 60s next week so I'll just wait for the temps to stabilize before I adjust pressures again. Maybe at that point I will deflate them down to 30 or so, then reinflate to 36 like I mentioned above. Just as an experiment.
Here is what the red alert looked like in my 2011.
Originally Posted by Darel
Maybe at that point I will deflate them down to 30 or so, then reinflate to 36 like I mentioned above. Just as an experiment.
I did that one time a few years ago on the way to the nearby tire inflator (don't have a heavy duty compressor at home). Stopped in the parking lot after the individuals readings were on the cluster and then let some air out to check out the warning system. Folks driving by probably thought I was crazy.
If you do it, please come back and post your results.
02-13-2018, 07:24 PM
