How does the tire pressure sensing system work?

I've always been intrigued by this. My new '08 GP has automatic tire pressure sensing. How in the world does it come up with the pressure of the tires?

I've always been intrigued by this. My new '08 GP has automatic tire pressure sensing. How in the world does it come up with the pressure of the tires?
That's a good question. I'm curious as well.
My guess is magnetically.
I had a flat in a truck with the air pressure sensing system and when I put the full size steel spare on the low tire light stayed on.
I wonder if there's a mag field sensing the distance from the source to the tire's steel belts or something like that. Surely a steel wheel would disrupt the field.
I may be out in left field though.

The GM TPMS system has been around for quite a few years now. I've seen it in action on late model Chevy Tahoes and Suburbans. This link should give you an idea of how it works. The one found with the late model Grand Prixs should be similar.

Click here (http://www.etools.org/files/public/Tire_Pressure_Monitoring_System_Update_from_GM.pdf )

The GM TPMS system has been around for quite a few years now. I've seen it in action on late model Chevy Tahoes and Suburbans. This link should give you an idea of how it works. The one found with the late model Grand Prixs should be similar.

Click here (http://www.etools.org/files/public/Tire_Pressure_Monitoring_System_Update_from_GM.pdf )

So just a pressure sensor with a wireless transmitter?

Left field it was :)

Thanks for the article. Sounds pretty high tech. FWIW, the 2008 GP owner's manual describes the procedure for the average Joe to reprogram the system when tires are rotated. No special tools needed.