Steve2150

On my tire pressures my air pressure gauge comes up exactly as the DIC but on OnStar diagnosis the pressure is not even on all tires and some 2 lbs less. Thought the onstar would be same as the DIC.

billeee

I've noticed low readings from Onstar. I think the reading are taken at night when it's less likely to conflict with a cell phone call and tire temperatures (and therefore pressures) are lowest.

Steve2150

As soon as I got the car in garage I went to onstar diagnosis and refreshed so it was only few minutes difference

billeee

Steve:

When I go to my Onstar account (PC web page) it shows tire pressure readings from the monthly maintenance check. How did you refresh it?

15Z06

I suspect he's actually refreshing the report in the smartphone app ?

iclick

I think that's right. If you'll look under the tire pressure status it says "Values were collected during the last drive." After an app refresh mine now shows tire pressures in what would appear to be a cold state, so I would assume it gathered that info the last time I drove when I first cranked it cold.

Checking the DIC just now to compare, it shows that all values except tire pressure are the same as reported by the app. It's obvious that the "...during last drive" notation applies only to the tire pressure and that all other values were pulled from the car when the app was refreshed. It seems odd it wouldn't pull the TP values as well.

meyerweb

I believe the TPMS sensors shut down when the tire isn't rotating. If that's right, neither the DIC nor OnStar can report current pressure when it's parked.

Steve2150

Yes, smartphone app. Just before I parked while on my street moving checked DIC, all 32 lbs but onstar reported after refresh lf 32, lr 31, rf 29, lr 29.

owc6

I don't worry about a pound or so difference in the phone app vs the gauge or DIC. They vary more than that based on which side of the car has sun shining on it. They are very low volume tires (despite their large appearance). A ten minute difference could make a few pound difference in measurement (depending on when the app is collecting data).

Vetteman Jack

15Z06

That could be the case with the vette - mine is new and I haven't tested it - but that's not the case with any other car I've owned, Chevy or otherwise.

owc6

Unless it has changed from the C6, The car doesn't check the tire pressure when the car is off (why would it? It's not going anywhere).

15Z06

Actually, no one said "when the car is off". The point was whether or not the system will reading/updating when the tires are not rotating and/or the vehicle is parked. I have aired up 3 brands of car in the driveway while using the onboard pressure monitor as reference.

To your point though: All cars were "off" (not running), parked, and not "going anywhere" at the time, which I find greatly simplifies the job ;-)

DavePowell

However... the OnStar reports are made only when the vehicle is running, so typically it would be in motion.

Dave

iclick

I put mine in service mode (hold starter button for ~5 sec.) to get the info I mentioned yesterday. It showed everything including TPS info, which I assume was in real time since the values reflected a cold state for tire pressure.