How does onstar know what tire pressure I have?

[FLYNNZL1]

How does onstar know what tire pressure I have? What on the car can read tis information?

[jpsuperman81]

I am fairly certain the pressure monitors are in the valve stems of the actual tires.

[FLYNNZL1]

I removed my back tires today to install my mud flaps and was just wondering, I didn't see anything???

I found this;
General Tire Pressure Information

Using data retrieved from your Tire Pressure Monitoring System, we'll let you know in your OnStar Vehicle Diagnostics* report if your tire pressure needs attention. You should check your tires monthly, at a time when you haven't driven for at least three hours.

* What is the Tire Pressure Monitoring System and how does it work?

Tire Pressure Monitoring System — If your vehicle is equipped with a Tire Pressure Monitor System (TPMS), it uses radio and sensor technology to check tire pressure levels in each of your installed tires. TPMS sensors monitor the air pressure in your vehicle's tires and transmit tire pressure readings to a receiver located in the vehicle. The TPMS is designed to alert the driver if a low tire pressure condition exists, and may also allow the driver to check tire pressure levels using the Driver Information Center (DIC) on your dashboard. If you have replaced your factory-installed tires or wheels, your TPM system may not be functioning properly. Check with your installer for compatibility.

Tire Pressure and Changing Temperatures — Tire pressure can change over time as temperature changes. The pressure goes up as temperature goes up, and pressure goes down as temperature goes down. (A good rule of thumb is that tire pressure changes 1 psi for a change of 10°F.) This can happen seasonally (from summer into fall), daily (from a cold night to a warmer afternoon), and while driving (the tires warm up as you drive).

You may notice during cooler weather conditions that the Low Tire Pressure indicator will appear when the vehicle is first started and then turn off as you start to drive. This is an early indicator that the pressure is getting low and tires need to be inflated to the proper pressure.

[soverydeb]

if you go and mess around with your vehicle information display, it will show you what each tire pressure is!

[zebra]

OnStar just uses the Tire Pressure Monitoring system information

[Andro]

There are TPMS sensors inside the tire, they are connected with the valve stems

[FLYNNZL1]

Thank you

[BryanB]

yea, you're not going to see anything unless you take the tire off the rim

[Rockytophummer]

Im not exactly sure how it works but the parts department at my dealership told me to never use fix a flat on these tires because the have a little cube shaped censor on valve stem that can tell your tire pressure and sends it to onstar. They say the fix a flat blocks up the sensor and it costs $100 to replace it. Dont know if this is for sure but thats what they told me and figured if its true then it might help with your question.