I have an April 2013 Model S. The original sensors are gen 1, and they don't show individual pressures. I found that places like Discount Tire will try to sell you the sensors, but they actually only have gen 2 type in their inventory. Furthermore, it requires Tesla service (or somebody VERY well versed in Tesla) to actually initialize the gen 1 to the system, they don't come on merely by driving a few miles like most TPMS.
When I had my gen 1 start to fail several months ago (while in warranty) , Tesla initially put me off. The problem mostly appeared in cold weather (like now) and until late summer it wasn't a problem. In October the problem returned. I tried to use Discount Tire, and they installed the gen 2 which was incompatible. Tesla honored the fact that I had reported the problem while in warranty and agreed to replace the TPMS for me.
The replacement, was to upgrade ALL my wheels to gen 2, and add the gen 2 functionality to my computer. I now have the individual tire display for tire pressures.
So, if you see all 4 tires on your display, Tesla has already upgraded this to gen 2.
And you can go to a regular tire place to get new sensors.