Tire Pressure Monitoring System and Cold Weather

Cold weather affects the tire pressure, as I recall: 1 lb/10 degF
It could be that you need to check your tire pressure.

 

"Yes" to both questions.

 

I've heard the pressure needs to drop about 25% from the set* pressure, before you get a warning. Just to get the obvious out of the way: have you checked the pressures?

* You can reset that level, explanation in Owners Manual, on page 443, albeit somewhat confusing:

The "few minutes" in step 5 confuses me: 5, 10, 15 minutes? I did this once, think I used 10 minutes.

The reset button is under the dash in vicinity of steering wheel: says "SET" and has a flat tire with exclamation symbol.

 

The attached TSB on TPMS Initialization specifies a minimum of 5 minutes. I was not sure about the few minutes. I used 3 minutes (few) when I increased my tire pressure and it appeared to work properly. I may have to go back and hold it for 5 minutes to make sure

 

Thanks for that!

A suggestion I've read, keeping in mind the possible 25% pressure drop needed to trigger the alarm, is to overinflate, say 15%, reinitialize the TPMS, and then reduce pressures to your normal. So that the TPMS is on more of a hair-trigger.

I've not bothered with it though: my set pressure is maybe 25% over spec. to begin with, so as long as it were to trigger when I went a bit below spec. that would be fine with me.

 

I thought about this and came to the same conclusion you did. I just had a screw in a front tire, and I was keeping the fronts at 40 lbs. and when the TPMS light came on, I checked the pressure and it was down to 30 lbs, and that was plenty of air to still drive on it. Visually, the tire looked the same as the other tires.

 

I had the very same issue as you with a screw in the tire. Same tire pressures and alarm points. I came to the same conclusion, also.

 

I don't know about the 1 psi per 10 deg F rule. I think it drops more than that. It will drop even faster if the temperature drops below the freezing point (most of the water vapour in the tire will freeze out to "snow").
I checked Pearl's tires about a month ago and found them at 38 PSI average, and they started at 40 PSI average a month before when the new Nokian WRGIIs were installed (yes, I run the fronts 2 PSI higher than the rears). I put in 44 PSI in the front and 42 PSI in the rear, anticipating further dropping. The temperature when the tires were installed was around 15C and a month ago it was around 10C. It's now around 0C. Heading for -20C in another month (DON'T RUSH IT!!).

It's not the TPMS working incorrectly, it's the temperature causing the pressure to drop. The TPMS is just warning you to CHECK YOUR TIRES!!! PLEASE CHECK YOUR TIRES!!!
We don't want any "Ford style" exploding tires on Prius! We have enough problems with idiots claiming failures in other systems already.

 

Your tire pressure is inadequate. Set the tire pressures at the lowest ambient temperature that the car will be operated in and this won't become an issue.

MB860 ?

 

i live in los angeles. took the car up to the mountains once there the TPM came on . i checked tire presssure and the tires .everything was ok. once i came down the mountain the TPM light went off. some times on cool days when i start the car in the morning the TPM comes on. Now its on all the time. tire place said everuthings ok with the tires and not sure why the TPM light is on.im waiting till i get some time to got o the Dealer to have them check it out.

 

When you turn on the car, does the light blink for about a minute, then stay solid? Or does it just come on solid from when you start the car? If it's blinking for 60 seconds then staying solid, you'll probably need to take it into the dealer. If the light just comes on solid from the start, try resetting the pressures with the reset button. It could be that they were set the last time when the pressures were high and you just didn't know.

 

Is there a reset button for the 2006? If so, I can't find it. I hate taking it to the dealer for everything!

 

not sure, did u check the o/m? might be under the steering wheel beneath the dash.

 

The TPMS transponders each have a battery. This is not a normal service item (TPMS "service" at tire changes apparently amounts to an o-ring replacement). Anyone out there know when the batteries start to die (and need replacement)? I'm guessing a decade might be about it.

(This, of course, assumes you have checked your tire pressures and used the reset button as described in the manual and you still have the trouble light.)

 

The TPMS "set" button is on the bottom of the dash close to the steering wheel. Put your head on the floor and look up. You put the proper pressure in the tyres, then press and hold that button until it responds (with a beep as I recall). I don't remember if the car has to be in "ready" or not.

You cannot replace the batteries in the sensors. You have to replace the sensors. Then you have to get the dealer to enter the new sensors into the TPMS system with the Toyota Tech tool. The sensors are not cheap, and neither is the dealer service! The sensors go -inside- the tyre (one bead must be "broken"), and the valve stems you see on the outside are part of the sensor.

 

I search through a pdf of 2006 Owners Manual (all I happened to have); didn't see anything. FWIW, our previous car was a Canadian 2006 model year (a Honda) and did not have any TPMS. I don't think Toyota would implement it unless they had to by regulation. Just Googling, I believe it became mandatory in new vehicles, at least in the 'States, as of Sept 01, 2007:

Federal Motor Vehicle Safety Standards; TPMS; Controls and Displays. Final Rule.

 

In the 'States you legally "have" to. In Canada, while new vehicles all have some sort of TPMS, from reading on Transport Canada website I don't believe it's mandatory to replace them if they fail, or if you acquire separate snow tires on rims:

Ask TC Road Safety - Transport Canada

 

On my 2009, you do this in "Ready" and hold the button in until the yellow warning light flashes on/off three times on the dash.

 

My tire pressure warning light flickered on as soon as the temperatures dropped so quickly into the 30s. A few days later of the cold temps and it came on and stayed on. I thought it would go back to normal when the temperatures got back to normal but, no. So I checked the pressure. It had dropped from 35 to 20! I got myself to the tire pressure thing at the gas station and all is well now.