does your 07 RX350 have a TPMS sensor on the spare tire?
 

my tire pressure light is on, my spare doesnt have a pressure sensor on it, just wanted to know if thats the problem.
I dont know if it suppose to have a sensor or not.

Yes; my 2007 350 has the sensor.

and my 2008 does as well

and my 2009 does, too.

How would you know? The sensor in INSIDE the tire.

I'm sure you have it. If by some magic (like the tire was replaced at one time w/o a sensor), the tire pressure light would be on 100% of the time. Those sensors are registered at the factory with serial numbers into your ECM. When one shows low pressure (or goes bad), the ECM lights the dash indicator.

There is no easy way to verify that these work as they are programmed by the factory scan tool. They CAN be broken at "Tire Stores" when you get new tires, alhough most are used to them now. I still make it a point when I get new tire to insist on the invoice they put down that the light is currently "off" before the new tires are put on.

They are rather expensive (around $200). You can get used ones ($20) on Ebay and various other places, but used ones are usless if you don't have access to a FACTORY scan tool.

TPMS sensors have metal valve stems. Tires without TPMS have rubber valve stems.

I've verified the spare on my 2007 has a sensor both by the presence of the metal valve stem, and by the fact that the warning light has come on (and stayed on) while all 4 service tires were properly inflated. Inflated the spare to the correct pressure, and voila! The light goes off.

Yes, the 2007 spare has a TPMS. I have had the light come on numerous times because of a low spare tire pressure. I now over-inflate the spare, problem solved.