So a while ago I had third party TPM sensors installed in an extra set of (MINI) wheels to use for snow tires. Everything was working fine. Then a few weeks ago I got a "low tire" light, when the weather got cold. I topped off all the tires, and everything was fine again.

Then the other day I stopped and got gas. Before I stopped the car everything had been fine. Then when I turned the car back on, I got "low tire" again, and it indicated all 4 wheels. So I went from zero "low" tires to four in the few minutes it took me to fill up the car? Weird... Once again this happened on the first very cold day in a long time, so I thought that might be it.

So I went to put air in the tires. I had filled them all to 40 a few weeks ago. Today 3 were at about 38, but one was <30. I filled them all back up to 40, and the alert went away automatically, without me having to reset the system.

So this raises a few questions-

How much of a PSI drop should you see with cold weather? I'd assume only a few...

Next- how much does the pressure need to drop to trigger the TPM alert? (or does this depend on the specific sensor?)

what I'm really getting at is- why did all 4 alert, if only one was significantly low?
if a pressure of 38 (down from 40) is enough to trigger an alert, i'd think the one at 28 should have alerted long ago!

Or (what I'm afraid of) is one low tire triggering all to go off? If so, is there any way to fix that? I'd really like for it to work as it should, and if a tire is low, it indicates WHICH ONE, and doesn't just say all 4 are low.

Is this a sensor programming issue, or a mini issue? Am I paying the price for trying to save a little money and buying non-OEM sensors?

Sorry for being long-winded, but thanks for your help!!

 

My understanding is the sensors ONLY report the psi they sense....YOUR CARS computer "listens" to the transmitted info...and it decides when to alert you....
temp do cause a psi drop...as high speed driving and hot tires do cause a psi increase....what logic tye mini uses to determine you are "low" is up to them....maybe somebody has read the software, but it sounds like it is working as intented...perhaps a hard turn into the gas station/pothole/curb caused the psi drop?

 

I wouldn't call a 38 PSI "low" when it's supposed to be 40, though... but if it is set to indicate an alert when the PSI drops by 2, shouldn't the really low one have gone off a while ago? I can't imagine it went from 40 to 28 in the time I was filling up.

I'm guessing that it sets off the alert when it's (say) 10 psi low. so the one maybe had been slowly losing air, then finally got to 29, and that set off the alert. Which is just what it should do.

What I want to know is- why did it say ALL FOUR tires were low?? Is that how everyone's works? Isn't it supposed to tell you which one it is? I'm just wondering if there's something wrong with my system in that regard.

 

I have a 2010 cooper and it doesn't differentiate between tires. Not sure if the newer models are supposed to tell you the difference. All its shows is the red flat tire warning. I have a bent rim so one of tires leaks pretty bad. I've seen it go off more than a few times.

 

A tire will lose roughly 1 psi for every 10F drop in temperature.

The TPMS seems to be able to detect about a 3 psi drop in pressure. It probably depends on what the pressure was when you last reset the system. It would be sensible if it took notice of the current pressure when you reset the system and tell you about a drop from there.

So if your sensors were reset at 31psi, then it wouldn't tell you till about 28psi. If you reset it at 40, it should alert you at about 37psi.

 

Ok, I just did a little experimenting. I filled all tires to 40. Then I let air out of 1 until the light came on. It seemed to take a drop of about 10 for it to signal, but, letting the air out wasn't particularly precise and we may have overshot.

Regardless- it indicated all 4 were low.

According to the owner's manual, it's supposed to indicate WHICH is low. (the warning light shows a little car with a triangle next to each wheel. In my case all 4 triangles are lighting up.)

I'm wondering if it's because the sensors I had installed were not OEM parts.

It's not a huge thing, but, I just wish it worked the way it says it should.