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Discussion Starter · #1 ·
has anyone noticed any problems with the tire pressure sensors? mine have been reading in the 36-38 range, which i verify on a weekly basis with a very accurate tire gauge that i have. all of a sudden, in the last couple of weeks, the dic is showing as low as 32 psi when cold, but it does go up to 35-38 after a few highway miles. even when cold, the dic has not shown such a low psi since i started monitoring tire pressures weekly back in April. my gauge is still showing 37-38 psi. the air temp here in texas is only about 10 degrees cooler (70 at night, 90 daytime) than during mid-summer, so it's not temperature related. now, i don't mind a psi or two difference, but when i see 32 psi on the dic i get nervous as to whether my tires are low, or not.
 

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Discussion Starter · #3 ·
read my post again; i think i made it very clear that the sensors have not shown that low a psi before. they have been showing about 36, then up to 38 on the highway.
 

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I had one recently that hit 33, then I pumped up the tires a bit. It's been cold at night and hot during the day here, so mine are all over the place. In fact, when I park my Acadia, the right side gets sun during the day and when I roll out of the lot, those are 37, the lefts are 35. They then get to 37 after a few miles.
 

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I read and understood your post. I was only passing on the information my service advisor told me when I voiced the same concern. If you mention to your service advisor what you mentioned in your email, they are probably going to tell you the same and that the fluctuation in psi is normal. The service manager was not willing to change my sensors unless they failed or became too erratic. To him, this did not constitute an erratic behavior.
 

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Discussion Starter · #6 ·
that is their standard answer for everything. i am not willing to accept that. tire pressures don't change that much.
 

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I agree with you 100%. When the service manager got involved and said it was final, my only option was another dealership or GMC customer service who referred me right back to my dealership. They wanted to give my dealership every opportunity to resolve the problem.
 

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If you are concerned about fluctuation in tire pressure, why don't you try putting nitrogen in your tires. The range should be much smaller, even under very cold and hot conditions.

just a thought.......
 

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If you're interested in finding out how big a difference temperature change has on tire pressure, all you need to do is use the formula PV=nRt.

P= pressure in mm HG (millimeters of mercury)
V= volume (ignore this since it is the same theoretically at all temperatures)
n= number of moles (ignore since this is the same in a closed system)
R= gas constant = 8.3145
T= temperature in degrees kelvin. This is really important. 32 degrees F = 273 degrees kelvin.

I'll let you do the math. It is easy to find the percentage change in pressure between 2 temperatures.
 

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quetico said:
If you're interested in finding out how big a difference temperature change has on tire pressure, all you need to do is use the formula PV=nRt.

P= pressure in mm HG (millimeters of mercury)
V= volume (ignore this since it is the same theoretically at all temperatures)
n= number of moles (ignore since this is the same in a closed system)
R= gas constant = 8.3145
T= temperature in degrees kelvin. This is really important. 32 degrees F = 273 degrees kelvin.

I'll let you do the math. It is easy to find the percentage change in pressure between 2 temperatures.
It is much easier to convert from Celsius to Kelvin since Kelvin is just Celsius + 273.

0 degrees Kelvin is absolute zero, by the way.
 

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Discussion Starter · #11 ·
all right wise guys, i realize that air pressure will change depending on temp.

my point is that the sensors have always read a certain pressure, which agrees with my gauge, but now they read quite a bit different from their norm, even though my gauge says the pressures are something different.

the sensors have shown about 35 or 36 psi since i've had the vehicle (april 2007). they go up to about 38 psi when driving on the road. now (and for you wise guys it's still hot here in texas), the sensors are reading 32 on some mornings, but not every morning, even though the same gauge that i''ve been using all along says the tire pressures have not changed.

i didn't ask for any formulas (that may or may not tell us anything), i just asked if anyone else has seen some flunctuations in the sensor readings. i've never had a vehicle with this feature, so maybe they all have a variance problem like this; or maybe none do and mine need to be replaced.
 

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Not to divert the name calling, but I just recently had my tires in the 33 range, as it's getting colder here in Maine. I went up to the local gas station (free air a rarity nowadays) and pumped mine back up to 37. Sometimes they get to 35 when they sit outside in the parking lot at work, but when I'm rolling, right back to 37. Amazing the difference in warm to cold weather.

I never had a vehicle that checked the airpressures before...I wonder what my Yukon tires were like last winter? Better piece of mind and gas milage this year!
 

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cravenfan,

I agree. I never did regular checks of my tires. Relied on service center to do it at service time or before leaving on long trips. With the new pressure sensors I am getting paranoid about it. Never realized it would change so much with the weather. Hard to keep up with it.
 

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I've noticed some changes in the readings, but nothing too out of whack. I've noticed that it's gone down noticably on colder days, and the pressure will go up after driving some. I've also noticed that I should top it off every month or so - that's normal, at least on most cars I've owned.

This past weekend, I was putting air in the wife's truck so I thought I'd top off mine too. usually, all 4 tires are the same (or within 1 PSI of each other). I notice d on the DIC that the left front was 38, and the right front was 35. This is highly unusual, but I noticed that the left front was in the bright sun and the right front was in the shade. I believe this is part of the difference.

I agree with the comment about Nitrogen - it's supposed to be much less susceptible to changes due to temperature.
 

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Okay, time to resurrect. I have a question pertaining to this old topic:

The factory tire PSI sensors, what is the tolerance? +- 2 pounds?

My metal cased hand held mechanical PSI gauge tolerance is +-2 pounds according to the Mfg. When the factory DIC reads 35 psi, my mechanical one read 37.

Anyone have a digital type tire gauge that reads the same as factory installed sensors? Just curious.

I go by the factory sensors, but use my mechanical tire gauge to meet factory sensor psi if 36-38.
 

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teetertotter said:
... Anyone have a digital type tire gauge that reads the same as factory installed sensors? Just curious.
...
I found my digital gauge reads the same as the TPMS (to the nearest whole number) whenever I fill my tires.
 
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