Tire Pressure Monitor System (TPM) Picture
This is a typical tire pressure sensor on GM vehicles. This is used on TPM systems in your Chevrolet, Buick, Pontiac, Cadillac, GMC and Oldsmobile cars and trucks.
There a differences between this part depending on model and year. Other sensors have a black stem. These must be pulled through the rim with the tire removed.
The picture above is the type with the nut on the outside of the rim. The tire still needs to be removed from the rim to replace. See picture of a tire pressure sensor below...
Complete description of the TPM System