How does TPMS work?

Assuming it's same system as third gen: you can change pressures, and then re-establish the system with that new pressure. There's a button under the dash that you push. Actually, if you google "Toyota Techinfo" and go to the "manuals" Tab, you should be able to download the Owner's Manual, see that instruction. I believe it has to fall a significant amount from the set pressure, maybe 20~25%? It doesn't care about higher pressures due to warm up, just a pressure drop.

 

it's pretty cool, really. there's a sending unit inside the tyre, connected to the schrader valve.

 

Well, "pretty cool" would be a readout of the -actual- pressure, a buzzer warning of dangerous deflation, and identification of which tyre is actually causing the warning.
As it is it's "pretty basic".
It just turns on a small light on the dash with a low tyre symbol in front of it when -any- tyre drops more than 20% from whatever set value you use.
Each sensor has an internal battery, and if that dies it's "new sensor time", at ridiculous cost btw. Though they do seem to last as I haven't seen a failure yet.

Oh, and I suspect the reason we don't see the actual pressure displayed is related to the cost AND, most importantly, the fact most people would panic if they saw how much the pressure actually varies with temperature!

 

I believe it will warn about being over inflated. It is just that the factory triggering threshold is likely way above the sidewall pressure. Remember a circulated story of someone that had the light come on, and just kept adding air, without checking the pressure, until the tires were up to 80psi or higher.

Can the owner relearn the system after a tire rotation? The Sonic requires a special tool to do so. Since there is only a single warning a light that doesn't state which tire is low, it doesn't matter to me if the car thinks what the left front tire is really the right rear one.

 

MiniVCI reports these values. Perhaps someone will snoop the traffic and post XGAUGEs to report.

Bob Wilson

 

Some do display individual readout for each tire, and I could have gotten the info off of the OnStar site while I had the trial subscription.

The batteries should last at least 5 years, and might go to ten. The goal is to have the sensors work until it is time for a new set of tires.

 

The sensors cost more than tyres. A lot more. And you -can't- put in a new battery. It's "cast in place".
The system doesn't care where each sensor is, in fact, they could be stacked in the garage beside the car and it would work. And does, just ask anyone who has separate wheel/tyres for winter and doesn't do the TPMS thing on the winter wheels. Of course when you drive out of the garage it looses the link to the sensors and gets upset (turns on the light, eventually).

I have even seen some cars sense the wheels of the car next to them, though that was an early system perhaps not using serial numbers.

"We are amused, but not greatly."

 

What David said. The cost and complexity of maintaining the system, especially with aging sensors and/or extra rims (for snow tires for example) eclipses it's purpose.

 

Shame people weren't conscientious enough to regularly check their tire pressures regularly then.

 

You should be able to inflate to your desired pressure and then press the TPMS button under the dash to set the alarm point. There should be nothing that should limit it to Toyota's recommended pressure.

 

Actually, I check my tire pressures more often than what the typical American does, but one tire picked up a nail, and the TPMS warned me about it before I had checked the pressures myself.
If I didn't think having the warning light on would be an automatic fail for the annual inspection, I would skip on replacing the sensors when they finally died, but only those that check their tire pressures before each drive would see no benefit from the system.

 

My 2006 Gen2 TPMS batteries are now going bad (2 out of 4) at 9.5 years and 150000 miles. MY2006 was the first year Prius got TPMS.

I got the Techstream miniVCI to read the pressures and minimize replacement costs. Right now I am just using it to zero out the bad tires to turn off the warning light. Apparently by law, repair shops are not allowed to disable the system, but with Techstream you can do so yourself.

I think Techstream shows my alarm point is 26.5 psia and I could change that in Techstream but I am not aware that pushing the button resets it on a Gen2. Just rented a lowly Cruze and they had all the pressures displayed right in front of me.