I have a question about the tire pressure monitor system accuracy. I find mine to be about 3PSI too low. When I picked up my Vette they were showing 32psi. I knew the pressure should be 30 but I drove with it for last weekend. I figure 2psi isn't bad. Today I used a tire gage and set them to 30psi. Cranked over the car and the TPMS showed 27 on each tire. Checked with another gage (digital) and it read 30 PSI so unless I have two tire gages that are the same but screwed up the TPMS is off by 3 psi. Does any one else have this problem? I guess I'll just keep them at 27psi which I know is close to the tire warning but the tires also heat up when driving. They all seem to be 3psi low so is there some kind of calibration to the system?

Thanks in advance.

 

I haven't seen it here lately, but supposedly you have to wait a little while after first starting your car to have the accurate numbers on the DIC from TPMS.

Most I've read about have maybe 1 or 2 psi off actual, good, unkicked around tire gauge.

Me, I use a tire gauge, a good digital that's been babied!

 

No calibration. Here is a previous discussion. It won't help but you may find it interesting:
http://forums.corvetteforum.com/show....php?t=1818489

 

Likely to find the TPMS sensors more consistent than gauges. I have several gauges in my tool box. Between the four of them, I would not be surprised to see 4 different readings. All within 3 or so pounds of each other but not consistant.

Also, as your tires warm up, the air pressure increases. This is why they say recommended pressure is 30lbs cold.

 

when I first switched to my new tires wheels it took about 12 miles before I got the TPS error message on the DIC. I was on my way to get them reset and once reset they read ok after that.

 

Click & Clack the tappet brothers did a study and found the inexpensive digital tire pressure gages to be relatively accurate.

 

I have an '07 and my readings are the same as yours. 3 lbs difference between the DIC and a digital tire gauge. My regular tire gauges show the same 3 lbs. I am at 4300 feet elevation. One of these days I'll remember to take my digital gauge with me when I go to the ocean.

 

I've got digital gauges (the babied kind.. ), the old and good pencil gauges and the DIC. Actually, all my non-on-car gauges read about the same. And all are about 1 lb off of the DIC.

 

The tire pressure sensors in the wheels are very accurate - they use the same pressure sensor mechanism your expensive digital tire pressure gauges use.

I have a TPMS tool with a screen and the sensors read out to the nearest 0.2 psi on the screen and are always almost exactly the same as my digital gauge (the difference being the gauge only reads to the nearest 0.5 psi).

The sensors send their data to the TPMS computer in the car which, I believe, is part of the RCDLR (Remote Control Door Lock Receiver module), which talks to the DIC through the car's computer bus (with maybe some input/output through the BCM). The data perhaps gets massaged some enroute to the DIC, but one built in discrepancy will be due to the fact that the DIC only reads out to the nearest 1.0 psi.

Butt.....the biggest thing that I think is giving you a difference in your case is that you need to drive the car to get the TPMS to update the DIC displayed pressures.

When the car sits still for more than 15 minutes the sensors go into the sleep mode and only transmit once every hour. When you start driving more than 20 mph the sensors wake up and start transmitting once every 60 seconds (sooner if they detect a large pressure change, like a flat).

So.....if you're checking your tires with your gauge, the DIC probably won't update until you go out and drive the car faster than 20 mph for several minutes. After doing that your DIC should read pretty close to your gauge measurements.

Forum members that live in high elevation areas above several thousand feet have reported that there can be a 3 or 4 psi difference between their gauge and the DIC. There's no "calibration" that can be done to the TPMS, so if you live at high elevation you just have to know that DIC readout will be several psi different than the actual tire pressure.

Edited: I just looked at your avatar and see that you're in Utah - probably above 4,000 feet. I think that elevation thingy is definitely what you're experiencing!! Go with your pressure gauge - adjust your pressures to 30 psi cold (or whatever cold pressure you use) with your gauge, and you'll just have to realize that the DIC will show 27. If you ever take a trip down lower elevation I bet your DIC will correspond real close to your pressure gauge reading.

Bob

 

Mine reads 2 psig low as well. One of these days, I'll check my pocket digital gauge against the deadweights we use at work, but I know the car DIC is low. I checked it against 3 of my pencil gauges and one pocket digital, and it's low. BTW - instrumentation is what we do at work - just because something has a digital display, does not mean it's accurate.

And I'm sure you know to check them cold. Even if you didn't - comparing DIC readings to your pocket gauge - they would both be affected the same by temp. Gotta laugh at the advice given here sometimes. It's like people don't even read what you wrote.

 

Thanks. I'll keep an eye on them. I agree it may be the altitude or maybe they were in sleep mode. Both of my tire gages read the same so I'm pretty sure they are accurate.

 

I've now had 2 different C6's, 3 different tire pressure gauges, 3 different TPS sets and have come to the conclusion that the TPS/DIC readings average 2#'s low compared to a good gauge. My tires are now set @ 29#F & 28# R with an accurate (expensive) big dial mechanical gauge. the DIC reads 27#'s F and 26#'s R. The same settings on my '05 gave very even tire wear and accepable ride/handling.

 

I have a 2007 Z06 and my TPIS is consistently 3 PSI below the tire pressure gage reading when the tires are cold. After reading this thread I believe the tire pressure gage and not the TPIS. The TPIS does indicate 30 PSI after driving the car and warming up the tires. The gage is still 3 PSI greater at 33 PSI.

 

Yep

 

I also live in Utah and use a tire gauge to reach the 30psi and the DIC shows 27. I also had an e-mail from on star saying my tire pressure was low, although I had 30psi with a manual gauge - I believe the gauge. The readouts on our Tahoe are more in line with each other.

 

Yeah, I get the same email from Onstar. It's wrong.

 

I think since the sensor is inside the wheel, it has no access to atmospheric pressure on the outside, like a tire gauge does. Because of this, it seems to me that the altitude would have an effect on the TPMS that it would not have on the gauge that we use to check the tires. I want to check them when I get to sea level and test this out. I also can't wait to see the extra power that the car will have there. The lowest I have been is 3000 feet and it had a chunk more power even there!