PSA: TPMS - System Warning and weather fluctuations

[NATO]

Not sure if this has been posted or not yet...

So last night I'm coming home from work. I start my truck and notice that the TPMS is telling me that all of my tires except for the front driver side tire are unacceptable low. So I get out of the truck and visually inspect all of my tires, and they all seem fine. I decide to drive home anyway. I leave the truck in the garage over night, and this morning when I get up to go to school, it only tells me that only the rear tires are low now.

Now, living in Saskatchewan Canada, usually at this time of the year the temperature is usually always around -20 degrees celcius (-30 or colder over night) but this year we've had a really warm winter. Last night was probably the first night that it dipped below -25. I kind of put 2 and 2 together and figured that the extreme fluctuation in the weather must have had something to do with the system warning.

Talking to one of the Tech's at work, he said that the MDX's have had similar issues. A simple, quick fix is to simply add an extra 2 ppsi of air to all 4 tires (Supposed to be 32, so I set them to 34). After that, started the truck and sure enough the system warning had gone off. I guess the engineers didn't take Saskatchewan into account when designing the tire pressure monitoring system parameters.

Anyway, I just thought I would share in case anyone else has ran into this and wasn't sure why...

Cheers,

NATO

[Truckin']

We've had the same low pressure warning on our coldest nights which has only been around 13 F (-10 C). BIGGUY used the same method of overfilling slightly and they've been fine since. We're having a pretty mild winter too.

[Lingered_I]

The TPMS warns at 24psi and then will only switch off the warning when the pressure exceeds 29psi. Your tires should be at 32psi, so a 5 or 6psi fluctuation due to temperature changes doesn't trigger a warning.

Fun with maths and physics

[Truckin']

So do you have any thoughts on why this happened to both trucks on a cold snap night? I know that it may be purely coincidental. Two occurrences is hardly a pattern.

On the morning ours came on it said three tires were low. We haven't had the warning come on during any other times. Oh, yeah. There was once when it actually was a slow leak in the tire.

Thanks for the cool link for explaining math and physics.

[WhiteRTLnav]

They should modify the TPMS to allow you to view the pressure for each tire. My TPMS has gone off a couple times, and each time, the weather was pretty crappy. If the system told you the actual pressure, you could decide whether it is a flat tire, or simply a low pressure tire, and address the system at the appropriate time.

[kanji]

I guess, i will never see my warning tpms light go off on me living in SoCal. In any case, i had the air in all 5 tires that's including spare, switched over to Nitrogen. Since Nitrogen has a larger molecule than air and doesn't get affected by enviromental temp unless it dips down really low.

[gonzo's rt]

Cold temps decreases tire air pressure. Hot temps increases tire pressure. That is the reason why you are asked to check your tire pressure when they are cold.

[shingles]

Originally Posted by gonzo's rt

Cold temps decreases tire air pressure. Hot temps increases tire pressure. That is the reason why you are asked to check your tire pressure when they are cold.

Exactly - there's nothing wrong with the TPMS... whenit's cold, air is more dense, you get less volume, thus less pressure. When it's hot, it's less dense, more volume, thus more pressure...

[moumou48]

According to what I learned before, roughly every 10-degree drop in temperature decreases 1 psi in tire pressure. This also happened to my brother’s Pilot. So the temperature is the culprit. But please do pay attention to the tire condition and not to fool just by the temperature.

[roakey]

Just some observations on the TPMS system and how it behaves…

We had our first real cold snap here in Colorado and I got a couple examples about how the TPMS system works.

I had the “horse shoe” (GF’s term for it – cross section of a tire) come on for the first time last week and it immediately identified the LF tire as low. A check with a digital tire gauge showed that it was a whopping 1.5psi low (30.5psi). I drove it home and planned to fill it up the next morning while the tires were cold. However, I ended up having to drive it that evening and didn’t have a chance to pump it up before driving. This time the horse shoe came on, but it didn’t identify which tire (LF) for at least a minute or two. Pumped it up the next morning, started the car and once again the horse shoe came on and immediately identified the LF as low. After about two or three minutes of driving, it finally went off.

Next day repeat the process, but RR tire, which turns out even closer to correct pressure – 31psi! More or less same behavior – it sometimes takes a long time for the TPMS system to figure out the offending tire, sometimes not. And it takes a very long time for the TPMS system to figure out a tire is up to pressure again.

This time I went around the entire car and put all four tires spot on at 32psi (LR was 32, RF was 32.5). Haven’t seen the horse shoe again – at least not so far!

So a couple observations about TPMS…

1) It doesn’t take much for the TPMS system to alarm – mine came on at 30.5 and 31.0 PSI. Maybe something to do with the altitude here in Colorado?

2) Be patient – it sometimes takes awhile (on the order of minutes, plural) to figure out which tire is low after the horse shoe comes on. It appears to know that something is low long before it can figure out which tire is low.

3) Be patient – after filling up a tire it takes awhile (again, on the order of minutes, plural) before it figures out that everything is hunky dory.

4) Given just how finicky the TPMS alarm is (only 1PSI!?!?!?), get a good digital gauge for accuracy.

Roak

Ps. I’m not upping the pressure by a couple PSI because, well, I’m an engineer and I want to see what happens running them at exactly 32!