TPMS light came on but no flat tires

[Lanister]

Hey guys. So on my drive home from work today, the Tire Pressure Monitoring System (TPMS) light came on red. I pulled over immediately thinking I have a flat but all tires appeared to be fully inflated. I didn't have a gauge with me to check so I visually checked again and got back on the road. As I was driving, I held the TPMS button to clear the warning. First it went from red to orange and then disappeared. I kept driving for another few miles and no light came on. Very puzzled as I set the tire pressures just a few weeks ago and there has been no major temperatures changes. I intend on checking the pressures in the morning but in the mean time I wanted to see if you guys know if the TPMS tends to misfire on occasion?

[kayger12]

I'm going to guess you have a slow leak in one of your tires and it's about 8-10 lbs low.

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[BavarianZHP]

Visually checking is tough on our 18" tires with stiff walls. I for one sure can't notice a difference of 10 lbs under-inflated. It's why I check mine fairly often.

I hope you don't have a leak. Not sure around your area, or if this is common practice, but there is a place in Seattle which will repair any leaky tire for free (in the hopes that your flat is actually irreparable so you can buy a new tire from them). Maybe have a look around?

[johnrando]

Def use a gauge. TPMS will come on with the air ratio of the tires being outside of a certainly tolerance. So, one tire could be lower than the others at minimum, and you would not be able to see that. Once you "air up", just press and hold to reset the TPMS.

[BRGcoopahS]

This happened to me a few times after getting a flat and putting on the spare. Just wondering, how does the computer know the tire is low on air?

[johnrando]

The sensors are just calculating the difference in the ratios... there's a good post on how they work. There are two versions, one which knows the air pressure, and ours which is just working on tire speed ratios IIRC.

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[LivesNearCostco]

Giya< do you have actual TPMS sensors in your wheels or the wheel speed tire pressure sensing system?

[Avetiso]

http://www.memecreator.org/static/images/memes/2221654.jpg

[Lanister]

I'm pretty certain it's just a standard TPMS system, which measures the difference in wheel rotation speed. I hope it's not a leak. I'll update once I check the pressures tomorrow morning.

Sent from outer space...

[Lanister]

http://www.memecreator.org/static/images/memes/2221654.jpg

True story

Sent from outer space...

[Hermes]

ours which is just working on tire speed ratios IIRC.


^This

When I put my style 68 spare on last year because of a bad sidewall bubble my TPMS went off. The wheel speed ratio was not the same on both sides

[danewilson77]

I'm going to guess you have a slow leak in one of your tires and it's about 8-10 lbs low.

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In for current tire pressure readings.

[Lanister]

Update. So I checked the pressures (cold) before driving off this morning and here's what I found. Rears were dead on the same pressures but the fronts were 38 PSI (Driv) and 35 PSI (Pass). Is 3 pound difference enough to set off the TPMS warning? Mind you, since I cleared the warning I put on about 20 miles and it hasn't come back. The only thing I can think of is that when hot, the pressure difference could be a bit higher, perhaps 5 pounds, which could be just enough to tip it over the edge. I'll check hot pressures this afternoon and update.

[danewilson77]

That 35 PSI may have been right at the threshold when cold?

[LivesNearCostco]

Likewise when I had my mini donut spare on, my TPMS light kept going off. I thought it was same diameter as the OEM tire, but maybe not.


^This
When I put my style 68 spare on last year because of a bad sidewall bubble my TPMS went off. The wheel speed ratio was not the same on both sides

[Lanister]

It would definitely be interesting to zero in on the pressure difference threshold. I'm sure that the type of tire would play a role too since different constructions (sidewall stiffness, etc) would yield different amounts of radius decrease from dropping pressures.

[kayger12]

Hard to tell anything from your current pressure without knowing what the pressure was when you calibrated the system. If the front was 40+ when it was calibrated 35 could trip it.

Hot/cold pressure shouldn't really matter. The system measures (indirectly) the departure from the calibration pressure.

[Lanister]

It's the first time I hear about calibration. How does that work?

Sent from outer space...

[kayger12]

When you press and hold the TPMS button it calibrates based on the tire pressure at that time.

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[kayger12]

At least that's my understanding.

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[Lanister]

Makes sense. So it actually tracks each wheel for rotation speed, rather than comparing them to each other, which is what I thought initially and so erroneously. So I suppose the reason it hasn't come back is because I've re-calibrated it for the new, lower pressure. So what happens when I restore the pressure back up to 38 PSI? Logic follows that a re-calibration would be in order. So would I expect the TMPS light to go off again? Even though the rotational speed has gone down rather than up?

[kayger12]

Yep-- I re-calibrate every time I adjust tire pressure.

[Lanister]

Should I expect the light to come back then? Or do I just work the button once again?

[kayger12]

Once the pressure is where you want it (cold pressure) I'd press the button and re-calibrate.

[Lanister]

Got it. Thanks :thumbsup

[kayger12]

Sure thing. Good luck!

[LivesNearCostco]

I don't have a TPMS button that I know of... and I don't have real TPMS sensors, just the wheel speed sensors. Lannister has a TPMS button. Does that mean he has pressure sensors inside his wheels?

[kayger12]

I don't have a TPMS button that I know of... and I don't have real TPMS sensors, just the wheel speed sensors. Lannister has a TPMS button. Does that mean he has pressure sensors inside his wheels?

Good question. I haz button.

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[Lanister]

I've gotz no idea. My guess is that I got wheel speed sensors too.

Speaking of tire pressures. Here's what my sticker inside the door says...

11633

Seems much higher than for Sedans, which are 32/38. Is that right?! Are coupes that much heavier?

Sent from outer space...

[kayger12]

I've gotz no idea. My guess is that I got wheel speed sensors too.

Speaking of tire pressures. Here's what my sticker inside the door says...

11633

Seems much higher than for Sedans, which are 32/38. Is that right?! Are coupes that much heavier?

Sent from outer space...

Weird. I have a coupe and mine is 32/38.


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[kayger12]

My sticker is for R tires, though, not ZR.

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[Lanister]

It seems like these could be max load numbers.

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[Lanister]

Checked the manual and it's 32/38 for regular load so that's what I'm sticking to. Set the pressures and re-calibrated TPMS. Now let's see if I have a slow leak.

[LivesNearCostco]

I *think* (without having read any documentation on it) that the wheel speed system tracks each wheel's rotation speed while the one with real TPMS devices tracks each wheel's pressure. I mean why track the wheel's rotational speed if you have a pressure sensor inside the wheel?

And last night found 3 tires are 1 or 2 PSI low, and front left is about 4 PSI low at 32PSI (I like to run 36/40, even though the spec is 32/28).


Makes sense. So it actually tracks each wheel for rotation speed, rather than comparing them to each other, which is what I thought initially and so erroneously. So I suppose the reason it hasn't come back is because I've re-calibrated it for the new, lower pressure. So what happens when I restore the pressure back up to 38 PSI? Logic follows that a re-calibration would be in order. So would I expect the TMPS light to go off again? Even though the rotational speed has gone down rather than up?

[Lanister]

What's your reasoning behind running higher pressures? I'm tempted to mess with it myself but I really don't drive it hard enough to be looking for improvements. My main goal is to get the most grip out of the tires in an emergent maneuver or a abrupt stop.

[LivesNearCostco]

I don't do higher pressures to get better traction (though in AutoX that's common to reduce tire rollover in hard turns, especially with stock springs and camber). I do it to reduce the chance of cracking my rim on a pothole, and to provide more safety margin in case one tire starts a slow leak. I've cracked two rims. Only problem is higher pressure are a slightly harsher ride.

[Lanister]

How hard of an impact does it take to crack one of these rims? They're pretty heavy so I would imagine it's not that easy to do.

[Avetiso]

How hard of an impact does it take to crack one of these rims? They're pretty heavy so I would imagine it's not that easy to do.

I think it would be easier with a heavy wheel vs. a light one, but it all comes down to wheel strength. Heavy wheels have more rotational and translational energy than a lighter wheel, so impacts would be heavier.

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[UdubBadger]

Slow leak in the beading is my guess, happens to me all the time


Goin' HAM mobile

[onepercent]

My TPMS light came on once when I was having some fun driving in the rain, throwing the tail around just a little bit at low speeds. The tire pressure was fine, but the slipping of the tires on the wet pavement caused the code. If you checked your pressure and it was fine after the light came on, I'd reckon you have this kind of false error.

[BRGcoopahS]

My TPMS light came on once when I was having some fun driving in the rain, throwing the tail around just a little bit at low speeds. The tire pressure was fine, but the slipping of the tires on the wet pavement caused the code. If you checked your pressure and it was fine after the light came on, I'd reckon you have this kind of false error.

That makes a lot of sense. I was having some fun today, noticed a slight slip and moments later the tpms light came up in red. Drove for a half mile "knowing" it wasn't flat and pulled into a parking lot. Much to my dismay, there was no flat. I originally thought it was the cold weather causing a drop in tire pressure. Then again the e46 system doesn't actually read tire pressure.

[Washburn]

I've only had the TPMS come on twice...tire pressures were near/almost normal... it drove me nuts for weeks on each occasion.
I or the tire place guys couldn't detect any flat tires in either of the times.
....not right away....
Both times it ended up being a VERY slow leak; one due to a nail and the other a bizzare shaped stone has embedded itself in the tire...
both occasions, the nail and the stone had 'sealed' the hole well enough by themselves, and no big air pressure could be seen, and only by total accidents did I spot the nail on that occasion. it was VERY hard to see. The stone was see by a second tire place dude.