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Discussion Starter · #1 ·
The monthly OnStar Vehicle Diagnostics Report that I receive via email includes (as well as other diagnostics) tire pressure on each of the four wheels that seems inconsistent with readings I have personally measured on each tire. The email I received today indicates three of the four tires are reported as having 33 psi and one 32 psi. I checked the "cold" tire pressures today with two tire pressure gages and both indicated all four tires are at 35 psi which agrees with what I set them at (using one of the two gages) a couple of weeks ago. I have seen the same trend before where the Onstar report has been lower than I have measured. My tires are the standard factory installed 18" Michelin Latitude Tour kind. Has anyone else experienced a similar difference or have an explanation for the difference?
 

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ebeno said:
The monthly OnStar Vehicle Diagnostics Report that I receive via email includes (as well as other diagnostics) tire pressure on each of the four wheels that seems inconsistent with readings I have personally measured on each tire. The email I received today indicates three of the four tires are reported as having 33 psi and one 32 psi. I checked the "cold" tire pressures today with two tire pressure gages and both indicated all four tires are at 35 psi which agrees with what I set them at (using one of the two gages) a couple of weeks ago. I have seen the same trend before where the Onstar report has been lower than I have measured. My tires are the standard factory installed 18" Michelin Latitude Tour kind. Has anyone else experienced a similar difference or have an explanation for the difference?
Tire pressure will rise and fall when the vehicle is in use. At the time they gathered the info for the report the numbers may have been correct and not what it may be currently. I am not 100% sure of how they gather that info, it could also be an average of the pressure thruout the month but that would be pretty pointless. IMHO including the tire pressure info is pointless but I guess for the people who dont check it often its a good reminder that your tires may need some more air.
 

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Yeah, it is just a report about a slice in time. Had you really has some serious loss of air pressure, the DIC would have told you at the time anyways.

Come to think of it, my first OnStar report told me that three tires were at 33 pounds and one was at 32 pounds. Hmmm...I wonder if it was the same tire (left front)? Maybe the OnStar report is an electronic version of a "bedbug" letter that gets mailed out once a month?
 

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Discussion Starter · #4 ·
In answer to jstpsntym, Onstar did report the left front as the one reading 32 psi while the other three were 33 psi. Same result he had experienced.
 

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I have this tire pressure gauge.
http://www.longacreracing.com/catalog/item.asp?id=1118&catid=8
I found that the DIC display in my Cobalt would read 2lbs low compared to my gauge.
My Terrain also reads 2lbs lower then the gauge.
Looks like GM wants us to over inflate the tires a bit.

My gauge has been compared to a known calibrated gauge that is by a pro mod race crew.
 

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Just got my monthly onstar report and it was lite up like a christmas tree The vehicle is at the dealers and getting a rear seal replaced and onstar is telling me to get to the dealer as soon as possible.. Dealer must have some connectors unpluged
 

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I changed the oil the other day. OLM was in the single digits. Ya, I know, I put it off to long.

The On Star report I got later that evening showed the old OLM reading and the tire pressure from the day before.

I'm guessing the On Star reports the pressure the tire monitors tell the DIC. Perhaps the sensors are off by a couple of pounds.
 

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The other day all my tires were running low. They had been low for the past few weeks at around 33 PSI. I had just driven about 20 miles so I figured they were warm and filled them up to 37 PSI. I get in, my DIC says 37 PSI so I figured good to go. Get in it the next day and my DIC says 39 PSI. This was after the car had sat overnight so the tires were "cold." Obviously alot can affect the accuracy of the tire gauges.

My 37 PSI that I filled was with an automatic inflator that shut off at 37 PSI and matched my pressure gauge and matched the DIC. So three things say 37 PSI inflated "hot" yet a day later they automatically gained 2 PSI while being "cold."
 

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fourmoremarine said:
Just got my monthly onstar report and it was lite up like a christmas tree The vehicle is at the dealers and getting a rear seal replaced and onstar is telling me to get to the dealer as soon as possible.. Dealer must have some connectors unpluged
hehe-- sounds like the Onstar report was run-- when at the dealer-- and they turned the key to do something.. but youre right-- something must have been disconnected.
 

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Just got the Dec OnStar report tire pressures reported fronts 32 and rears 33. DIC showed fronts 34 rears 35 hot.
 
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