You might notice that when its cold out, your tire pressure sensors will go off. I found out why tonight! My uncle is a sales manager at a chevy dealer and so I thought I would ask him since I noticed my dads caddie was doing the same thing so it must be a GM deal. He said it took them forever to figure this out but they are pretty sure they solved it!

Turns out the anti-lock brake system monitors each individual wheel speed. If it senses one tire running faster or slower than the rest continuously, it will attribute it to a problem with the tire until the system realizes that the condition does not change and it will clear the message automatically and adjust the system! So when you first turn it on with cold tires, it notices that the pressures have dropped and so has the diameter of the wheels. Until it learns the new diameter, it lets you know that your tire pressures were lower than they used to be!

So if you check your tires as I did when it was cold out, I found I had 3 at 33psi and 1 at 34. He said its a sensitive system but that one tire might be enough especially with the large tires to make the wheel turn a little different speed. If you make sure your tires are all at the same pressure, it should not happen as often but if you put it away warm and start it up cold, it will probably still give the error

 

Good anwser. You think GM would have this fixed. They have to be tired of fielding calls for it.[&:]

 

This just hit me but I remember people talking about changing stems with new rims because of the pressure sensors in the rims.
I have a feeling there are no pressure sensors in the stems. This is because I was looking around and there is only tire pressure monitoring on 4 tires. The spare is not monitored. Usually for a TPM system, there is one reciever mounted in the car and not one for each tire. So it doesnt matter how many sensors it monitors.

There are direct systems which use a sensor in the stem and a indirect system which only uses the ABS to detect a change in wheel speed to relate to diameter and thus, pressure.

Just a thought, but it seems to make the most sense to me. If I was GM and making a cost efficient off road vehicle, I would go with an indirect system. It also explains why we cant see the actual PSI's

 

Not so. The TPM goes off while you are airing down your tires to go offroad. It does this before you move the vehicle. If it relied on the ABS sensor, the tires would have to turn before it would know something is up. Also, after rotating your tires, you need to tell the TPM where each tire is, and the way you do that is to let air out of each tire in a sequence until the horn chirps, then move to the next.
If you look at the stems, you will see that the actual stem is rather large and metal, and has a hex head on it for a wrench. If it were a regular stem, it would be rubber, or if GM did go to the expense of metal stems, they woule be narrower.

 

Linus is correct..The TPM valve stems have a transponder on the inside of the tire/wheel attached to it...Importkiller *Mike* has a picture I think of his somewhere, posted here.

 

Now I knew if I hung around here long enough, I would learn some things. Thanks Ghost...I just recently noticed this issue as well and was a bit surprised as temps had only dipped to low 40's - high 30's. Of course it immediately resets itself as I begin to drive. I see eventually someone here will invariably cover any topic/questions I have.

 

http://www.etools.org/files/public/T...te_from_GM.pdf

I found that picture that mike posted. Its actually a caddie rim. That article has interesting information if it is the same sytem. The part about disconnecting the battery and losing its connection makes me wonder.

The stem does look similar though.

If it is, i wonder why we dont get a notice telling us which tire is low.

And why do we have an indirect (ABS) and direct (Stem) monitoring system?

And why doesn't it monitor the spare?
http://www.gmbuypower.com/pages/subm...9801AAD0DEDE99
all the way at the bottom "4 Tire Pressure Monitor does not apply to spare tire."

 

That low, in South Florida!
Miami, FL

CURRENT CONDITIONS
70°F
(21°C)
Mostly Cloudy
Rel. Humidity: 60%
Wind: NNW at 6 mph (10 km/h)
Sunrise: 6:45 AM
Sunset: 5:30 PM
Barometric Pressure: 30.09"Hg (F)

 

That low, in South Florida!
Miami, FL

CURRENT CONDITIONS
70°F
(21°C)
Mostly Cloudy
Rel. Humidity: 60%
Wind: NNW at 6 mph (10 km/h)
Sunrise: 6:45 AM
Sunset: 5:30 PM
Barometric Pressure: 30.09"Hg (F)
[/quote]


Ummmm no LOL...1st time about a week and half ago in the NW GA mountains, and a couple nights ago near the Ocala area where I happen to be spending the T day holiday.

 

the pic I have posted is of a caddy but it is very similar to ours and looks the same so you get the idea. Our h3's do not use an abs sensor system, instead EACH wheel well area has it's own reciever...look around and you'll find them. This is a direct air pressure monitoring system, nothing that has to do with wheel speed or anything else. New Fed. regualtions require this system now. The vette's system and cassy is differant I believe, especially in how you have to calibrate the system when you move a rim to a different location. The reason why the system goes off when it is cold is simple......air pressures fluctuate with different outside temps. which is why you supposed to check air pressure and fill when tire is cold.