OnStar Diagnostics Report- TIRES.

[myold88]

Today I received an OnStar computerized diagnostic report via Emailed with green, yellow, red boxes along with a short note on each mechanical catagory. All is Ok but it says all 4 tires are at 30 PSi instead of 36 PSI.
I'm wondering if this could be a computer glitch or due to the colder weather now hitting New England. It's in the 30's here now in the early A.M.'s.
I guess I'll have to go check my tire pressure but @ 1700 miles it seems odd all 4 tires would be down exactly 6 pounds on my 2SS.

[SSOOCH]

It's the cold weather. I'm in Utah and its getting around 36 degrees here over night and I'm getting reports that my tires are around 30-31psi as well.

[Dragoneye]

The DIC should tell you the tire pressures, too...right?

[lcmc]

I put 35psi in mine but my car only shows 31. Is there a way to calibrate the sensors?

[68/2010]

I think it's messed up myself. I had all mine done at 36 and the computer said 40, 41 and 38,39. On star is never the same. Sp, I don't know what to believe.

[beegroovie]

Originally Posted by myold88

Today I received an OnStar computerized diagnostic report via Emailed with green, yellow, red boxes along with a short note on each mechanical catagory. All is Ok but it says all 4 tires are at 30 PSi instead of 36 PSI.
I'm wondering if this could be a computer glitch or due to the colder weather now hitting New England. It's in the 30's here now in the early A.M.'s.
I guess I'll have to go check my tire pressure but @ 1700 miles it seems odd all 4 tires would be down exactly 6 pounds on my 2SS.

FWIW, all 3 montly OnStar diagnostics that I've gotten since I took deliver all say the tires are low (31psi). The DIC and the tire gauge say they're fine. This happened in warm weather also, so I don't think it has to do with the outside temperature.

[Andro]

Same here my report says they are low but when I check tire gauge there fine,

[anthonybyram]

Get a good tire pressure gauge, use it,and trust your instincts. Kinda of old fashioned but has proven successful for alot years!

[jrhaus76]

Originally Posted by Dragoneye

The DIC should tell you the tire pressures, too...right?

It does.

Originally Posted by lcmc

I put 35psi in mine but my car only shows 31. Is there a way to calibrate the sensors?

You can. Its in the DIC, it says reset. The horn will beep a few times when you hit it. Very strange.


Mine does it all the time. Don't worry about it and don't over inflate them. if it is cold out and the car has not been driven, the air compresses and the pressure is low. As you drive, the tires heat up, the air expands and the warning goes away. if you get the warning and fill them up in the cold, the tires will warm up, the air will expand and you will be over inflated. Best advise... on a decent day in the 60s, drive the car around a while doing osme turning to heat the fronts up too and go fill them where you want them using a pressure guage and then ignore onstar. If the warning comes on in the DIC, take a quick check to make sure you are only a few pounds off and go on your way. It is a good idea to check incase you actually do have a leak. If it reads 20psi.. you have a problem. Expansion/contraction only changes them a few pounds and if you run low 30s you will get the warning alot.

Second way to eliminate it is go and have them filled with nitrogen. Expansion/contraction is much less.

[Supermans]

Don't listen to Onstar or the tire gauge in the car.. It is rarely accurate. Buy yourself a digital tire pressure gauge and once a week check them. I also bought an inflater and every week it is down from 36 to 35/34 when cold. That is in 75 F weather in the morning. The moment you start driving around, the tire pressure goes up and down depending on how you drive. Always check the pressure when it is cold and in the morning to be consistent.

[Banshee]

If you have pressures set at 36 cold and it is 70 degrees out, the pressures will drop 5-6 psi at 30 degrees.

Always fill tires when it will be coldest out..both ambient and tire temp.

A digital gauge should be used regardless what the DIC states.

Same holds true from winter to spring...You have 36 PSI and a 70 degree day hits. Your cold pressures will be 42 psi.

[Dragoneye]

Originally Posted by Supermans

Don't listen to Onstar or the tire gauge in the car.. It is rarely accurate.

I'd like to disagree with this...My experiences with the system have always been within 1 psi of the actual pressure.

[97one]

Originally Posted by 68/2010

I think it's messed up myself. I had all mine done at 36 and the computer said 40, 41 and 38,39. On star is never the same. Sp, I don't know what to believe.

It varies with the outside temp.
And rises after you drive & they heat up.

[calflan]

Reset your tire pressure sensing at the switch on the steering wheel. I had a tire indicate low pressure - warning from car sesning system illuminated. I reset the pressures and all was fine. Pressures were a tad higher than before reset. Like any monitor system I suppose it can get corrupted or misinform. Just reset and see what you get.

[Dakota Kid]

My report said the same thing, 30-31 psi all the way around.

I bought a digital gauge and filled em all to 36....

[Master1545]

Mine did the same thing this morning. It was cold early in the morning and as I was driving. It displayed 31psi on the rear right tire. As I was driving along, the warning went away. If it comes on again today, after it gets warmer, then I'll use a digital tire pressure gauge to check it.

[Naunna]

One day while driving to work, I didn't get out of my neighborhood when I felt a lump, bump type of ride. I stopped, did visual, kicked the tires and drove off. I felt the lump still and check the pressures on the DIC. One was 34 and the others 35. I did get the email from OnStar, so I took it to dealer and they put nitrogen in the tires and set them to 36.

Felt it again this morning due to cold weather. I checked and they were off by 3. I just hope that the lump & bump won't affect my driving in bad weather.

[chevyss]

The first cold snap we had, my tire pressure monitor came on. Tires were at 30 instead the 36 I put in them three days prior. Got to let the summer air out and install winter air and everything will be OK!!!

[incustody]

Ok I am glad that I am in smarter company. I was going to post a question why I am getting so low tire pressure reading all of a sudden. At 2k miles the nitrogen should be ok but it is staying around 31-33. So I will check with a real pressure guage. Another question though, if you have nitrogen in the tires and you are starting to get low how do you get them filled? Will the dealership still charge you $70 for a 4 tire filling if all you need is 2 psi in each tire? I don't think you want to mix normal air with the nitrogen filled tires.

[CamaroSpike23]

Originally Posted by 68/2010

I think it's messed up myself. I had all mine done at 36 and the computer said 40, 41 and 38,39. On star is never the same. Sp, I don't know what to believe.

Originally Posted by Andro

Same here my report says they are low but when I check tire gauge there fine,

get a new tire pressure gauge and check it. I carry at least 2 with me when I check my tires. 1 dial style and one piston style.

[AZ2SSRS]

Originally Posted by incustody

Ok I am glad that I am in smarter company. I was going to post a question why I am getting so low tire pressure reading all of a sudden. At 2k miles the nitrogen should be ok but it is staying around 31-33. So I will check with a real pressure guage. Another question though, if you have nitrogen in the tires and you are starting to get low how do you get them filled? Will the dealership still charge you $70 for a 4 tire filling if all you need is 2 psi in each tire? I don't think you want to mix normal air with the nitrogen filled tires.

My dealer delivered the car with nitrogen in the tires. (I didn't pay for it). I was told that I could stop by anytime to add nitrogen, but that's really not practical. I was also told that I could add regular air to the nitrogen at any time which I have. When I took the Camaro in for the recent service bulletin, they bled the tires and filled then up with nitrogen. My point here is that I doubt that any dealer would charge $70 (yikes!) to add nitrogen. If they do, go with regular air.

[BackinBlackSS/RS]

Onstar uses the same sensor your DIC does to read pressures right? My DIC has been exactly as my hand gauge. I also get the emails stating my tire pressure is low and sure
enough they are exactly what they say. Works great for me.

[jtzako]

My two rear tires read 33 instead of 36 on my latest report, and sometimes dip as far as 31. However, when they are warmed up from driving they are at 36 or 37. My other digital gauge agrees with the built in ones so far.

[Maclain]

Originally Posted by Banshee

If you have pressures set at 36 cold and it is 70 degrees out, the pressures will drop 5-6 psi at 30 degrees.

Always fill tires when it will be coldest out..both ambient and tire temp.

A digital gauge should be used regardless what the DIC states.

Same holds true from winter to spring...You have 36 PSI and a 70 degree day hits. Your cold pressures will be 42 psi.

When gases heat, they expand, hence the higher tire pressure when hot.

Look at your pressure when very cold, go drive the car "vigorously," then look at the pressure again. You will see after a long bout of driving hard that the tire pressure has increased due to the heating of the tires, which causes expansion of the air within, which is contained in the same volume space that the cold air was, which causes the pressure to raise.

My question:

So the correct tire pressure should be measured when cold? Wouldn't that overinflate them when tires have warmed up?

[SGOS252382]

My DIC has been giving me inaccurate information. I dropped both my rear tires down to 27- 28 psi at the track. It took a long time (several hours and a long drive home) before I got a low tire pressure warning. Then it only said 1 tire was running low on air.
This has happened twice after going to the track. So I'm not 100% confident in the system.