Tire low pressure warning light (!)

So did airing up the spare turn the light out? Because on third gen there is no TPMS sensor on the spare; not sure about second gen.

Good Public Service Announcement though: the spare is the "forgotten" tire. Doesn't help that you have to remove it to check pressure I guess.

Also, I wouldn't go the tape route. It's a little bitty light, there's a few others commonly lit that rival it. Tape'll gum up the clear plastic too. We live with that light every winter with our snow tires. Come spring, regular tires back on, light goes out.

 

Well...the spare tire does not have TPMS in USA Prius, at least not for Gen 2 or 3.
I'd be surprised to hear overseas Prius had that, as TPMS is basically a USA legal requirement.
Something unusual going on there.

Keeping spare tire adequately full is an issue.

 

@wjtracy has extensively researched the second gen tpms sensors dying on second gen, due to ailing batteries. Could be a borderline battery?

 

OK I guess they call that anecdotal evidence. Either your spare is actually equipped with a TPMS ( a few have made that mod) or it was a coincidence.

 

no mention of the other 4 tyres while the light was making you crazy?

 

TPMS light problems solved!

Just to support what KJ Fitz suggests trying. I, also, suddenly had the TPMS light come on. It happened on the freeway just as I was starting a short road trip. I freaked out and pulled off and checked all the tires. All OK. I had just checked and aired them the night before. I ignored the light since there wasn't anything wrong and nothing I could do. I read the owner's book and tried resetting the TPMS. Light blinked three times slowly and then stayed on.

When I got home I started reading Prius Chat to see what was up. From what I was reading, it looked like one of the tires might have a dead battery. Since I had just replaced the tires a year ago I didn't want the expense of removing them to find the one with the dead battery. Then I read KJ Fitz's post! Since it cost me nothing to try and it's a good idea to check the air pressure in the spare anyway, I figured, why not?

Well the spare was at 26psi. I pumped it up to 60psi, went through the TPMS reset procedure, and the light went out and has stayed out for 24 hours. I don't know if the spare has a sensor or if it's magic but I don't think I'll ask.

So if your TPMS lights up and all four tires have good pressure you might want to check the spare. Maybe it won't fix the problem but it might prevent you from having an unusable spare when you really need it. And it costs nothing.

In retrospect, it seems like a good idea to have a sensor in the spare since no one ever checks the pressure and it would be a bummer to have a flat spare when you have a flat tire. It just would have been nice if the owners manual mentioned to check the spare if the TPMS lights up. It would also be nice if the spare was installed so that the valve was up, not down, so you don't have to remove the spare to check the pressure and refill.

2006 Gen 2, 130,000 miles

 

hmm...very few Gen2s have TPMS on the spare tire.
I can think of one energetic Prius Chatter here who reprogrammed his system (hat tip @RobH).
I don't know if a few other owners did this mod (eg; via dealer assistance).

One thing to keep in mind, sometimes when you reset the system, it can take the system a long time to realize there is dead TPMS battery. You have to run the vehicle about 30-minutes for the system to realize there is a dead reading (because the old good pressure reading just stays in the memory banks until the system gets around to looking for a stale reading). So if you only do short trips, your TPMS light can stay off a long time even though there is a stale reading.

I solved the spare tire pressure-up issue with STAYFILL which is an expensive heavy gas for bicycle tires. I probably will not do that on my new RAV4H spare due to much bigger mini-spare (more costly)..

 

And what does your retrospect tell you about saying that in the owners manual if one is present ??