Everyone has had the TPMS light come on in both hot and cold weather alike whenever the tire pressures dropped below the threshold that triggers the TPMS warning light.

I do not know what the threshold is for these cars. I have read that on some manufacturer's TPMS systems, the threshold was ridiculously low — the tire pressure was extremely low and unsafe by the time the warning light came on. This was back in the early days of this technology.


Check your tire pressures and tell us what they are … and I'll share further useful information with you, my WI friend. :)

Do they charge you a fee for this?

What do you do if the dealer is closed?

Or, were you joking? :)

Nitrogen fill for tires is just a rip off. If it really worked to slow tire seepage then all tires would eventually be nitrogen filled as the O2 supposedly seeped out.

Water vapour is a problem if the compressor you use isn't properly serviced. Nitrogen fill is completely dry.

The biggest issue is ambient temperature change requires constant adjustment of cold tire pressures.

For every 10 degrees F (5C) approximately the relative tire pressure of your tires changes by 1 psi, approximately. This is because the tire is a sealed air chamber and proper tire profile depends on shape resulting from the correct relative pressure between inside the tire and outside.

As winter approaches you need to add air to your tires just o maintain correct relative (measured) pressure. Your TPMS only responds to relative pressure. If you do not add air and ambient temperatures drop by say 40C your TPMS is likely to trigger as this drops indicated tire pressure by 8 psi approximately (for example from summer temperatures of 30C to minus 10C, so stop laughing as here they go from plus 35C to minus 35C a drop of 70 degrees changing tire pressure by a massive 14 psi).

If you filled with nitrogen its back to the dealer for every tire pressure change unless you buy yourself a nitrogen cylinder.....

I believe TPMS triggers at a 20% drop in pressure. As you say, this is ridiculously dangerous.

The real problem is still drivers ignorant of the need for constant monitoring of tire pressure. The technology can display actual tire pressure and temperature in real time as Porsche does. The senders are very accurate. Porsche had this system on their magic 959 which actually used hollow air filled alloy wheels connected to the tire chambers and real time on the move air pressure adjustment operated by the driver or co-driver. Now that's what we need.

However, the majority of drivers wouldn't know what they were looking at much less how to interpret it. The tire pressure goes up and down with ambient temperature and tire temperature. This is why the Porsche system is fitted. Porsche assumes the driver wants to know actual tire pressure in real time AND knows what the numbers actually mean.

Not quite correct. No air escapes from your tires. Air pressure measured in a tire is relative pressure. When ambient temperature drops the outside air becomes more dense and exerts more pressure on the outside of the tire. Meanwhile the air inside the tire contracts (matches the density of outside air). Measured pressure and actual tire shape changes.

Fill a balloon indoors and take it outside in winter and you'll see exactly what happens to your tires.


TPMS was mandated for run flat tires because they don't change shape as the air inside contracts nor do they handle markedly differently when tire pressure is low, except in emergency maneuvers. Run flat tires are actually dangerous without TPMS.


Now everyone in the US (and now Europe) has to have this useless system fitted. Canada doesn't because it would be too irritating to the ignorant and useless for the informed. It gets very cold up here in winter. Our BRZ come with good old nickel plated brass valve stems. $5 bucks each to replace!

It's not a useless system. I enjoyed having it in my corvette where you were able to display the psi reading for each tire. The scions half assed version is not near as useful since it's basically an idiot light warning, even though you can see each individual tire pressure via techstream. Toyota chose to cheap out on our system. It however helps the clueless ones who wouldn't notice low air or a flat tire because they are too busy talking on their phones..

Those four fist-sized patches of rubber, the only contact my car has with this earth, are the only thing standing between me and St. Peter.

I pay close attention to them.

And I would pay for that, too, provided it did not cost more than, say, $50 per car. ;)

But since getting America's drivers to pay any attention at all to their tires is so difficult... :(

Sure it does, although not much. The generally quoted figure is one psi per month pressure loss. Not much, to be sure, but it contributes to the overall reduction in tire pressure over time if one's tires are left unattended over long periods, as so many are.

So, @Scionshaun...

What are your tire pressures? :)

The dealership where I work has this Nitrogen program, and from what I've seen, it is a complete waste of money.

Everything, including air, expands when hot, and contracts when cold (with the exception of water at freezing point, but that's another story). This is how everything around you works. For examples, hot air balloons, wind, internal combustion engines etc. It's all science, so don't blame the car's TPMS, it's done nothing wrong.

This may lead to confusion.

You're free to pump up your tires with "regular" air at the gas station if you don't mind the loss of the minimal benefits of nitrogen-filled tires. The nitrogen gas will eventually be replaced with the O2 over time as you regularly adjust your tire pressures.

Yes, racers use nitrogen, but that's to have a more predictable pressure change as they come up to temperature on the track (as I understand it). Realistically, that's not something that matters to us road drivers.

So, everyone...

Do you have a tire pressure gauge in your car?

I bought simple pencil gauges at Walmart for $1. They measure within 1 psi of my fancy Intercomp gauge. These inexpensive gauges are good to keep in one's glove box in the car. I recommend one in every car. The "gauges" at the gas station have typically been dropped too many times and abused to the point that one cannot rely on their accuracy. I've seen them be way off. Use your own gauge.

The life of you and your family is riding on your tires.

Drive safely, have fun, and don't jeopardize the rest of us out there. :)

If I'm not mistaken, TPMS warning light will come on if a sensor reads below 27 PSI, or the difference between 2 sensors is greater than 5 PSI.

My dealer told me to only fill it with nitrogen. Not all scions come with nitro filled tires.

:word:No they do it for free. If the dealer is closed then i just wait for the next day, its not like your tired will flaten or blow up.