TPMS (tire pressure) malfunction (?) on 2015 Prius V

Odds are good one of the sensors is bad.

 

Agree. TPMS batteries have a finite time and cycle life.

 

On our 2006 we had one TPMS go bad at 9 years, the other three lasted several more years. In any case, sounds like one of the TPMS has died. In most cases no TPMS on the spare.

 

Maybe time for a new gauge too. Is this a cheap digital?

Too, if all your regular tires appear to be ok, and your gauge is says the spare's at 15 psi, definitely look into it. Has it ever been topped up?

 

The button under the dash is used for setting what tire pressure you want the system to check for. When you have all four tires inflated to the pressure you want, if that is different from the originally programmed pressures, you use that button to have the car remember your new pressures. It will then give the warning at a threshold some % lower than those.

If you haven't changed your mind about the pressures it's already programmed for, then what that button does isn't anything you care about.

Does the warning light on the dash come right on solid after the car is turned on? (After going out once, briefly, after the lamp test) Or does it come on blinking for a minute or so and then go solid?

The solid-from-the-start version is normally trying to tell you about an actual pressure issue. The blinks-then-solid version is telling you about a problem with the TPMS system.

Do you have a scan tool that can show you the TPMS trouble codes? If not, I believe you can blink them this way:

Blink (a/k/a Flash) Codes – How to. | PriusChat

 

Probably indicates the transmitter inside one of the tires has used up its battery.

Pretty much any tire place can dismount the tire and swap in a new transmitter and mate it to the car and send you on your way.

You face the question of whether to just replace the one that's conked out (the tire place should have a handy wand they can use to see which one that is), or all four because "if one battery went, how far behind can the other three be?".

Sort of a matter of taste. Some will go for all four. I just changed my first conked-out one a couple years ago and am still waiting for the next shoe to drop. If a deer jumps on my car in the meantime, I never need to buy the other three.

Also kind of depends on the tire place you use, and whether they'll give you some discount for doing all four, or if it's just four times the cost of doing one.

 

Or just leave ‘em be, at least until the next tire replacement.