Tyre pressure warning system

[CMJToyota]

The tyre pressure warning symbol illuminated this morning on my Yaris. I haven’t driven it for a week and it has sat in a lot of water contaminated with leaves. After about ten minutes of driving it disappeared. How reliable do you find the system? Does it throw up a lot of false warnings?

[Mojo1010]

My car does that sometimes also, as well this usually happens after the last air input a few months back. Time to add some air to them. 

 

[Roy124]

I found it reliable. 

I had what I thought was a false reading on my Corolla that 'went away after 10 minutes'.  

I think it was Frosty that told me that the warning may not occur until 20% below the set pressure. 

Why did it go out?  The pressure in a cold tyre is less than in a hot one.  In my case the temperature was below freezing a few minutes after I set off.  When the tyres warned up the warning went out. The warning did not recur (before I checked the pressures a while later) as it was not as cold. 

If it is not a wheel specific warning you will need to check them all when they are cold .  If only one is 20% below then that suggests a slow puncture. 

[FROSTYBALLS]

TPMS doesn't tend to throw up many warnings as it usually only reacts when it detects an  approx 20-25% loss in pressure. Eg:

https://mag.toyota.co.uk/how-does-tpms-work/

However, if the weather is cold where you are and, as you said, it has been stranding in water for about a week, the system may well react to the fact the tyres will be very cold and at a low temperature  - which may be enough to throw up a warning on the TPMS.

The fact that the warning went after the tyres had warmed up, is probably corroboration of the system reacting to the low initial temperatures of the tyres.

[CPN]

(what others have already said and...)

Not really false warnings but up/down drifts in pressure as the ambient temperature changes. For example, if the TPWS system was set during the summer when the ambient temperature is higher, say between 15-20°C, even though the tyres were cold when the system was set for the correct pressures and then you get to winter and the ambient temperature suddenly drops by as much as 10°C, you'll find that the pressures will plummet by a lot; triggering a warning.

Easiest way to stop warnings happening because of this is, once the autumn/winter weather sets in, set the tyres to the correct pressures when they are cold (haven't been driven on for an hour or so) and then to re-initialise the system for those pressures following the procedure in the manual. You could probably leave them set like that for all year round and never get a warning (unless you get a puncture of course!). However, you may find the tyres feeling "harder" than normal during the summer if it happens to be a hot one...

[FROSTYBALLS]

Or you could increase the tyre pressures by, say, 3psi, reset the TPMS at the higher pressure, then reduce the tyres pressures to what they were before. This provides a slightly greater tolerance.

For example if the recommended pressures are 32psi - the system will show a warning when it detects a pressure loss of around 6.4-8psi. By resetting the system at a slightly higher pressure of, say, 35psi, the system will show a warning when it detects a pressure loss of around 7-8.75psi. Which may be enough to counter the effects of low temperatures affecting the readings

[Jimota]

I think my TPMS activated twice in the last 3 years during the summer months.  On both occasions it happened when travelling over particularly bumpy roads and only one tyre was affected.  After resetting the pressures in the onboard computer everything returned to normal.

[Cyker]

It's deffo the cold weather; My fronts were nearly 41psi in the summer but they were down to 33 on the weekend - That's how much difference temperature makes!

It also shows why low tyre pressures are so dangerous - At such low pressures, tyres have a lot more flex, which creates a lot of heat from friction, and that heat increased the tyre pressures enough to cancel the TPMS/TPWS warning!

This is why keeping an eye on your tyre pressures will let them live longer too (And also give an mpg improvement as it's not wasting so much energy to that friction heating, reducing rolling resistance!)

[TonyHSD]

I adjust my tyre pressures almost every week or minimum once every two weeks. Always on cold with separate pressure gauge and tyre inflator plugged into 12v outlet. Takes 10 min but saves me £000’ of fuel bill and tyre changes., and the car drives good, comfortable and quiet, plus grip is always at its best. 

[Cyker]

I used to do it every fortnight to a month, but that is one of the super awesome things about the Mk4 and I assume the new TNGA cars - They show the pressures the TPMS is sensing!

I don't know why this wasn't done from the start as the data has always been there, and it just makes so much sense! This really should have been available on the first TPMS-equipped car IMHO.

I love being able to watch the pressures in semi-real time while I'm driving and don't have to actually check them so often, except to raise or lower them.

It's quite interesting seeing how much difference there is; They can vary by a surprisingly large amount - It's not uncommon for the sun and high-speed driving to make it increase by 5psi from cold!

 

[CMJToyota]

Reading the various posts would suggest that pressing the hidden reset button resets the warning threshold to the current pressure which seems bizarre as I would have thought that it would reset it back to the factory datum.It would be useful if the system told you which tyre was faulty. Having read the Toyota article the system is far more complex than the tyre pressure system of an Airbus!.

[FROSTYBALLS]

2 minutes ago, CMJToyota said:

pressing the hidden reset button resets the warning threshold to the current pressure

Which is usual, and takes into account the need to adjust pressures for when one is carrying loads such as luggage, etc.

Some cars don't have a manual reset - on our i20 adjust the pressures, drive the car for a short distance, and the system resets to the new pressures.

[CMJToyota]

The difference in pressure for loads in the Yaris is tiny and fails to make allowance for the accuracy of the measuring system.

[Cyker]

There is no factory default they can be reset to - The TPMS sensors are not specific to the tyre/car/rim so they can't know what the pressure is supposed to be - The whole point of the reset is to tell it what it should be.

The closest thing is they will be set at factory, and if they are never reset they will keep that setting until the coin cell runs out.

But once the driver or whoever resets it, it's up to them to set the pressures correctly.

When I went from 17s to 15s, they were (supposedly) reset to the new higher baseline pressures for the 15s.

[RobertR]

11 hours ago, TonyHSD said:

I adjust my tyre pressures almost every week or minimum once every two weeks. Always on cold with separate pressure gauge and tyre inflator plugged into 12v outlet. Takes 10 min but saves me £000’ of fuel bill and tyre changes., and the car drives good, comfortable and quiet, plus grip is always at its best. 

If you have time a will to do that why not(if you are testing grip limit on daily basis 😄 ). I do that maybe twice a year and no problem at all.

[super-skier]

Our tyre pressure warnings came on for all 4 tyres almost exactly 1 year after delivery of the car. The garage said to just reset them as the pressure was correct. Not sure why they showed warnings.