Tire Presure warning lamp?

NISMOrob · Dec 12, 2008

Ok, for the last two mornings, when I start the car I get the yellow tire pressure light. I drive about 7 miles on the freeway to drop of my kids. When I restart the car the light is gone. It has been fairly cold the last two mornings low 40s(NorCal). Was wondering if this might just be due to the tires being cold. Wish the warning light would say which tire is triggering.

Anyone else have this issue?

coolmazda5 · Dec 12, 2008

One of the tires might be bordering 17-19PSIs when cold. I've seen that on mine. That somehow seems to be the lower limit for the sensor(s).

Just check the PSIs, and yeah, it is annoying not to know which one it is.

I've learned a little when I visually inspect them, but still is not that obvious with low profile tires...

08M5GTGSP · Dec 12, 2008

NISMOrob said:
Ok, for the last two mornings, when I start the car I get the yellow tire pressure light. I drive about 7 miles on the freeway to drop of my kids. When I restart the car the light is gone. It has been fairly cold the last two mornings low 40s(NorCal). Was wondering if this might just be due to the tires being cold. Wish the warning light would say which tire is triggering.

Anyone else have this issue?

The tire pressure warnings on both my M5 and my partner's Saab started sounding at about the same time a couple months ago when it started getting cooler, so I'm sure it has to do with lower pressure due to temperature. Funny thing is, I had a new set of tires installed in October, and my tire pressure warning hasn't sounded again since. I know I made the installer aware of the TPM system....

SparcEE · Dec 12, 2008

PV = nRT
where P=pressure, V=volume, n=moles of gas, T=temperature, R is the gas constant which is dependent on the units of pressure, temperature and volume

Ideal Gas Law...temp is a factor.

SparcEE

08M5GTGSP · Dec 12, 2008

SparcEE said:
PV = nRT
where P=pressure, V=volume, n=moles of gas, T=temperature, R is the gas constant which is dependent on the units of pressure, temperature and volume

Ideal Gas Law...temp is a factor.

SparcEE

Wouldn't manufacturers have a way to compensate for that in the sensors somehow???

NISMOrob · Dec 13, 2008

Thanks for the replies. I know that the pressure rises with heat, just was not sure if sensor was supposed to compensate for the change in temp. I will buy a gauge tomorrow.

coolmazda5 · Dec 13, 2008

08M5GTGSP said:
Wouldn't manufacturers have a way to compensate for that in the sensors somehow???

The TPMS on the Mazda5 just checks for very low pressure so don't trust the thing to alert you for a 29-30 PSIs low inflated tire.

The 2 times the TPMS alarm has come up on mine is when I was running with a slowly going flat tire (damn screw). 1st time the pressure was 10PSIs and the 2nd time, after I inflated it and left overnight, it was 17-19PSIs (cold). Light went away as soon as I got to the gas station, but after checking it was only ~20PSIs so that made me "guess" the threshold

blacktalon13 · Dec 13, 2008

SparcEE said:
PV = nRT
where P=pressure, V=volume, n=moles of gas, T=temperature, R is the gas constant which is dependent on the units of pressure, temperature and volume

Ideal Gas Law...temp is a factor.

SparcEE

are you a science teacher??? hahahhahaa i feel like i'm in my old science class

rweatherford · Dec 24, 2008

Use a real guage people! No matter what the temp you should have at least 30-35 PSI in your tires when they are cold.

I run over 40 PSI.

Tire Presure warning lamp?

NISMOrob

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