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Discussion Starter #1
OnStar sent monthly report and it said my tire pressure was 31 in all four tires. I went to gas station to add air, and all 4 were 35psi?OO :banghead:[/color]
 

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paulfdoig said:
OnStar sent monthly report and it said my tire pressure was 31 in all four tires. I went to gas station to add air, and all 4 were 35psi?OO :banghead:[/color]
PRESSURE IN TIRES CHANGE...when onstar read the pressure it may have been cold out and you just started the vehicle. Did you check DIC to see what it read before you went to station . Pressure could have gone up as tires heated up
 

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There's another thread that mentions how the TPM seems to be off a few pounds compared to manual readings
Search around............
 

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My OnStar report said the same thing. I drove from work home and watched the pressure in each tire go from 31 to 34/35 as they warmed up. Cold weather often causes the pressure in a tire to go down. But the tire pressure when cold is the "correct" one. You should check your tires first thing in the morning to see what the cold pressure is and add air accordingly.
 

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Discussion Starter #5
it was 6pm, car was cold, pressure has been the same for a few days, when ndone manually
 

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paulfdoig said:
it was 6pm, car was cold, pressure has been the same for a few days, when ndone manually
But they weren't cold after you drove to the gas station and there is no guarantee that their guage is correct.
 

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My DIC readings are not accurate either. They used to be. I DO know that. They've slowly gotten less accurate. Now they are about 4 lbs off. I use a good gauge for my readings.
 

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Air temp really makes a difference in your tire pressure. At least a +/_ 6psi. Try filling your tires with nitrogen. It costs a little more but its much more stable in extreme temp variations. Good luck.
 

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SoCalSRX said:
My tires have nitrogen in them. Is there any downside to topping off with air?
You are adding 80% Nitrogen to the supposedly 100% Nitrogen gas within the tire. I would go back to the place that put the Nitrogen initially, and ask them to top off the tires - FOR FREE !
 

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Costco does the nitrogen air when you purchase tires from them. As for the tire pressure sensors. I would stick with the manual method to determine what my air level is.

J. Carm75
 
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