# Tire Pressure Notification



## glambi (Sep 15, 2012)

I get those low tire pressure warnings from on-star all the time. I have nitrogen in my tires and the pressure seems to change A LOT with outside temperature change. I've had to make a trip to the dealership a handful of times to get more nitrogen put in my tires because they were low. Very annoying.......but I am trying to play along with the nitrogen vs. compressed air experiment.


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## Silver Streak (Jan 5, 2013)

I have personally found that on my Cruze (2012), the RR tire Always reads lower than the rest using the car's monitoring system. I have verified by using a digital tire pressure gauge together with a source of air at home, so I am setting all tires to 36 psi when cold. Yet, the RR will still show 1 to 2 pounds lower in the car. Had tires rotated, and the RR still reads lower, even though I watched that particular RR tire get rolled to the LF position. So, not an issue with the TPM sensor in one tire. Appears to be a reception issue - or something. I am not bothered (much) by this because I will check at times with an actual tire gauge.


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## lilmrsyeti (Mar 3, 2012)

When we first bought our car, before we drove it off the lot, we started it up and the TPMS came on and showed the right front tire was low...27# I believe it was. So the salesman took it to the service dept and had them put air in it. Less than a week later, it came on again for the same tire. Took it to the dealership again and they ended up finding a nail in it...so they plugged it and put more air in it. To this day, almost a year later, we have to put air in that tire at least once a month.

Yours is probably just the cold weather, but you'd think it would lower all the tires, wouldn't it?


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## obermd (Mar 3, 2012)

Richard said:


> I just got my monthly Onstar Report and I noticed there was a tire pressure notification for my right rear tire. They say the recommended pressure is 35 lbs. My right rear tire is showing 32 lbs. I have my car 2 months and I noticed that the pressure was always a pound or 2 lower in the right rear tire than the other tires. By the way, all of the other tires say 34 lbs. When I got the car, the pressures were 36 or 35 in all tires except the right rear tire said 34. I'm not getting any tire pressure messages in the car itself. I don't know if I'm going to add any air. It's been quite cold the past couple of days and it seems to have lowered the pressure by about 2 pounds in all tires. Also, I'm sure Onstar got its reading when the car was not in use. The pressure always rises when you drive. I'm kind of surprised that 3lbs under would trigger a warning from Onstar.


Do you have external confirmation with a good tire pressure guage that your tire is low? If so, inflate it and keep an eye on it. You may have a slow leak in that tire. I recently had one of my tires plugged - it took almost two hours to find the leak. Tires do get damaged and the TPMS will show a slow leak if you pay attention. Also, you don't have to wait for On-Star to tell you you have a slow leak. All Cruzen have a TPMS display that shows what each TPMS is reading. This makes it real easy to check your tire pressures with the press of just a couple of buttons. I check mine every time I start my car and the car has been off for more than a couple of hours. Just remember to run the TPMS relearn after you rotate your tires.

Also, the TPMS sensors are not 100% calibrated. This means you need to inflate cold with a known calibrated system and then look at your TPMS to find the difference. My ECO's TPMS read 2-3 PSI low.


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## obermd (Mar 3, 2012)

glambi said:


> I get those low tire pressure warnings from on-star all the time. I have nitrogen in my tires and the pressure seems to change A LOT with outside temperature change. I've had to make a trip to the dealership a handful of times to get more nitrogen put in my tires because they were low. Very annoying.......but I am trying to play along with the nitrogen vs. compressed air experiment.


I hope you're not paying for the nitrogen. Remember, compressed air is 78% nitrogen anyway. Nitrogen is useful in race cars because it doesn't expand with heat as much. It's also useful in your spare tire because no one remembers to check their spare until they need it and pure nitrogen won't react with the metal in the spare wheel or the rubber in the tire itself, potentially extending the life of the spare. Maxxis, who makes the spare donuts for GM, only warranties them for 5 years from manufacturing.


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## GoldenCruze (Dec 18, 2011)

Tire pressures are determined with the tires cold. In cold weather you often have to add air to the tires so that the cold pressure reading is correct. In hot weather, maybe let air out, although almost nobody does that.

The idea that a tire with low cold pressure reading becomes safe when it warms up is not the way to go. You are still rolling on an under inflated tire until it warms up. The fact that tire pressures increase when the tire gets hot is taken into consideration by the engineers when they determine the cold inflation pressure.


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## Richard (Dec 1, 2012)

lilmrsyeti said:


> a month.
> 
> Yours is probably just the cold weather, but you'd think it would lower all the tires, wouldn't it?


Actually, the cold weather did lower all of the pressures from 1-2 lbs. When I got the car 2 months ago, all the tires read 36 or 35 lbs. except the RR read 34. It was about 20 degrees warmer today and the RR read 33 cold and it eventually went back up to 34 as I was driving. All the other tires went up a lb to 35 as I started driving. So they're basically back to where they were when I first got the car.

I noticed that the TPMS is very sensitive to cold weather, more so than hot weather. On my Malibu, the recommended tire pressure was 30 lbs and when it got really cold outside, they all dropped to 25 or 26 lbs. It's funny - when that happened to me, there was a big line at the air pump in the gas station. Everyone who had the TPMS was probably getting a low tire pressure warning. I never checked the pressure with a pressure gauge. I wonder if the tires were really that low, or if it's just the TPMS reading unusually low in cold weather.

By the way, 35 lbs seems high. I have the LT1 with the 16 in tires. Is the recommended pressure 35 lbs on the models with 17 and 18 inch tires?


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## Richard (Dec 1, 2012)

obermd said:


> Do you have external confirmation with a good tire pressure guage that your tire is low? If so, inflate it and keep an eye on it. You may have a slow leak in that tire. Also, you don't have to wait for On-Star to tell you you have a slow leak. All Cruzen have a TPMS display that shows what each TPMS is reading. This makes it real easy to check your tire pressures with the press of just a couple of buttons. I check mine every time I start my car and the car has been off for more than a couple of hours. Just remember to run the TPMS relearn after you rotate your tires.


I check the tire pressures every couple of days and they always read a very consistent pressure in each tire. The RR has always been 1-2 lbs lower than the other tires from the day I got the car. It never went lower than 34 until a couple of days ago when the temperature dropped to 25 degrees. Today, it was 43 degrees and I noticed the cold pressure was 33 and when I drove a couple of blocks, it went back up to 34. Also, I never got a low pressure warning on the DIC. I can live with the pressure being slightly low by a lb or 2. With the way the temperature varies, you'd be adding and taking out air every couple of days. I usually add air when the pressure is consistently 3 lbs lower than the recommended pressure.


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## obermd (Mar 3, 2012)

Richard said:


> By the way, 35 lbs seems high. I have the LT1 with the 16 in tires. Is the recommended pressure 35 lbs on the models with 17 and 18 inch tires?


35 PSI is the door placard pressure on the ECOs. The Max PSI on the ECO tires is 51.


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## NickD (Dec 10, 2011)

Can't say I exactly miss those emails from OnStar showing the same exact information I can read off the DIC. 2012 2LT says 30 psi on that driver's side door pillar placard. Also run 30 psi, and my gauge is traceable to NTIS standards. 

Pay far more attention to that gauge then these made in China tire pressure monitoring system readings. Not too bad, seem to be within a +/- 2 psi variation.

Temperature is not the only variation, also atmospheric pressure, both weather and altitude, filling tires at one bar or 14.5038 psi pressure presents a differential pressure. Say if that tire was put in a vacuum that tire pressure would skyrocket.

Can really get nit picky on this subject, what the heck, if above 30 psi, really doesn't make that much difference. Or even a couple of psi below.


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