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[Boostin335]

Hi guys,

This morning, btw its -3 degrees outside in north NJ... my red tire warning light came on the dash, and also the yellow 1 above it on the background.

I went to gas station, car drove fine there.. and all pressure is fine...

I went in to reset it and when i clicked reset it said tire low above the reset button.

With the stock 17" run flats on my 08 335xi coupe... if the tire is low will the pressure show its low even though its run flat?

I am thinking the tire sensor is fucked and it isnt the tire... the pressures were all good and tires looked good.

Would I have to bring it in for service and have them do something to check?

[968tomr]

When it was cold outside (-1f), the TPMS showed all 4 tires were low - I didn't check the pressure before I added, but once I put air in and bled it down to the correct pressure the warning turned off.

-Tom

[hipnotic]

check the air in all four tires in the morning and then reset it on your idrive. you will then be good to go

[ceb]

You will never be able to visually see if a RFT is low.

Check your pressures and adjust as appropriate. Then reset your system. The sensors have a very low failure rate.

What year car do you drive? Perhaps the wheel well sensor has been damaged or is covered in ice.

[Me_Hi]

it's normal for that error when sudden changes in temperature. The air volume contracts when cold and dilates when hot, affecting the air pressure inside the tire. Also, if you recently changes your tires, this error will show. Put some air in the tires to your spec and reset the sensor. Make sure when the warm weather comes back that you check the air pressure as it will be a bit higher than what you just put in.

[iflyjetzzz]

I'm down here in Tucson and replaced the RFTs with a soft high performance tire in October.
In late Dec, I had all four tires indicate low pressure during cold wx but they looked fine. I filled all tires with more air and no problem. Until the latest cold snap (just over a month later); one of my tires gave me the low pressure warning. I filled it and checked the rest of the tires, topping off a couple of them. The next day another tire gave a low pressure warning ... I reset the system and it hasn't bothered me since then.

I was warned by the tire salesman that, due to large temp variations, I'd have my TPMS indicate low pressure several times a year here in Tucson. Anyone else experience this?

[Me_Hi]

of course....air changes its volume/pressure with temperature variations. That's why you see soo many people with deflated tires in the winter. They don't adjust for the temperature difference.

[iflyjetzzz]

Yes, I'm aware that pV=nRT. I think that just about everyone that posts here understands the interrelationship between temperature and the pressure of gases.

However, I've had my TPMS give me an underinflation alert approximately one month after filling my tires. And it's not like temperatures down here in Tucson are all that low; our lowest temp has been approximately 18 degrees.
Given that, I would expect those that live in the great white north to refill their tires every day, as driving heats up their tires and then the tires cool as the car sits for hours. But I haven't seen such a report.

To clarify, I've tried multiple resets on the TPMS while driving to get the caution to go away as the internal tire temp increases... sometimes it does, sometimes it doesn't. The TPMS system just seems a bit touchy to me.

Or is this because some tire brands retain their pressure better than others? My current tires are Continental ExtremeContact DW, a max performance summer tire. I like the tires very much and if refilling the air every month is the price I pay, so be it. But I would think that if a lot of other people were experiencing TPMS alerts on their cars (across all brands, as TPMS is now required equipment), there would be a lot more news/media/internet coverage about TPMS.

[1997gtx]

^ I've had to fill up my Cont. DWS tires a couple times this winter already. I'm dealing with slightly colder temps than you, but I think you're underestimating the effects of the cold(er) weather. I do agree, though, that these sensors are super sensitive. Not horrible, but certainly annoying. The last time I filled up the tires, I only had a 3psi difference. And, I also assume that some tires/rims are better than others.

[ceb]

Originally Posted by iflyjetzzz

Yes, I'm aware that pV=nRT. I think that just about everyone that posts here understands the interrelationship between temperature and the pressure of gases.

However, I've had my TPMS give me an underinflation alert approximately one month after filling my tires. And it's not like temperatures down here in Tucson are all that low; our lowest temp has been approximately 18 degrees.
Given that, I would expect those that live in the great white north to refill their tires every day, as driving heats up their tires and then the tires cool as the car sits for hours. But I haven't seen such a report.

To clarify, I've tried multiple resets on the TPMS while driving to get the caution to go away as the internal tire temp increases... sometimes it does, sometimes it doesn't. The TPMS system just seems a bit touchy to me.

Or is this because some tire brands retain their pressure better than others? My current tires are Continental ExtremeContact DW, a max performance summer tire. I like the tires very much and if refilling the air every month is the price I pay, so be it. But I would think that if a lot of other people were experiencing TPMS alerts on their cars (across all brands, as TPMS is now required equipment), there would be a lot more news/media/internet coverage about TPMS.

It is very simple. TPMS is required to alert you at the latest when the pressure drops 25%. Therefore, if your tire is set for 40psi then your alert should come no later than 30psi. TPMS will not alert you to overinflation so if your tire (based on tems for example) goes to 42 or 90 you won't get an alert.

Every 10 degrees in temp is about 1psi and a tire normally loses 1psi per month.

I think one can say that our tires are around 38psi so you should get an alert around 30 psi. If you get the alert every month then your tire is either leaking or your TPMS is broken.

[ceb]

Oh, if you find that your tires are not losing air, but you think your sensors are too sensitive then try this:

Fill your tires to a few psi below what you want (ie 35psi if you want 38psi)

Reset your system and assure that all warnings are cleared

Fill your tires to 38psi

That way you have another 3psi to play with.

[iflyjetzzz]

Originally Posted by ceb

Oh, if you find that your tires are not losing air, but you think your sensors are too sensitive then try this:

Fill your tires to a few psi below what you want (ie 35psi if you want 38psi)

Reset your system and assure that all warnings are cleared

Fill your tires to 38psi

That way you have another 3psi to play with.

So resetting the system recalibrates it to whatever amount of air is in the tire? If that's the case, I can't why multiple resets didn't clear the problem.

[Small Block LSX]

I just had this happen. I had all four tires indicating that they were low. After a day or two it changed to only one tire. I went to a gas station and put in maybe just a few psi of air and it went away and hasn't been back since.

Our temps were -25 and then +30 within just a few days.