ginway,

You don't list enough info here. When the light comes on do you find a tire that is low? If you have a tire that continues to go down, you have a hole in it and it will need to be fixed. Also, remember that your spare has a pressure sensor as well, so you may need to add some air to it if the other 4 tires are good. If all 5 tires are close to correct, you may need to calibrate the system. The process is talked about it in your manual, but you may want your dealer to do this if you aren't comfortable. My understanding is that the pressure sensor IS the valve stem, and not in the rim. Anyone else have any thoughts?

Brian