Tire light on 2007 Prius hatchback. Tire pressure all OK on all four tires. Tried resetting holding the Tire SET button for three flashes, etc. I could not make the indicator go away. My Prius was quite smart. My local mechanic caught it right away with his diagnostic tool. Here's why: I have a full sized spare in my trunk that includes a tire sensor equipped steel wheel. This fifth tire was under-inflated. When I pumped it up to normal pressure the tire light went away. Something to think about if you have a tough time with the tire light!
I don't know if you can register 5 TPMS sensors onto a single car. It's more likely your tire sensors have low battery and is not registering. You probably will have to replace all of them very soon due to low battery. They normally need replacement after 10 years, they will all start to fail one at a time Luckily the prices have come down a significant amount from when these cars were new. You can get a set of quality sensors on Amazon for about $50 now.
Some Toyotas do have the option of having a (full size) spare with a TPMS sensor that's monitored by the car. Didn't know the Prius had that option though. Posted via the PriusChat mobile app.
Pretty sure you can on a Prius. This Techstream image is of the TPMS PIDs from a RAV4, but I've seen the same from a Prius:
