OnStar Diagnostics Report- TIRES.

[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.

[strobi]

I put 32 lbs in mine cold...when they are warm they are 36-37. I found that if I put 36 in cold...they ride rough and are 40 or more when warm... SENSORS...What useless, expensive pieces of CRAP!

[Kept-a-rollin]

Originally Posted by strobi

I put 32 lbs in mine cold...when they are warm they are 36-37. I found that if I put 36 in cold...they ride rough and are 40 or more when warm... SENSORS...What useless, expensive pieces of CRAP!

I'm not a tire expert, but I interpret the instructions like this ... inflate tires to 36 PSI when cold means exactly what it says. If you inflate to 32 when cold, it sure seems to me that your tires are under-inflated. It shouldn't matter if 36 PSI cold increases to 40 PSI when warmed up. The 36 PSI when cold is the RECOMMENDED pressure. It's not the MAXIMUM pressure. I haven't seen anything that says 40 PSI when warmed up is over-inflated. My eyes aren't as good as they used to be, but it sure looks like the maximum tire pressure listed on the Pirelli P-Zero 20-inch tires is 50 PSI. So if the pressure is not coming close to max, should not be a problem.

By the way, I like the TPMS. It's working fine for me.

[TJ91]

Originally Posted by 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.

i love Onstar and im surprised by the TPMS, its really accurate on my car