Tyre pressures warning light

[Haliotis]

A couple of days ago, this warning light came on.  I checked the tyre pressures and all had dropped to between 29 had 30 psi, from the specified psi.  I am assuming the drop was a result of the recent sudden sub-zero temperatures - in the same way that they increase in pressure when the tyres get hot.  Today I increased the pressures to 34psi, but the warning light stayed on until I went through the reset procedure.  Does this mean that it is necessary to go through reset every time the light comes on?

[Primus1]

I think so, I had exactly the same question I posted a few days ago, I reset the system but I think you have to drive it a bit to calibrate it, though I could be wrong..

[Paul john]

Adding relatively warm air to a cold tyre may show a false uplift of 4psi. So when the system stabilises it may drop again. Reseting the system helps but a 4-8 psi drop will not affect performance..

[Cyker]

I didn't have to when I reinflated mine from the 20psi I get sent out with.

I did have to drive around for a bit before the light went out tho'.

 

[Paul john]

Just now, Cyker said:

I didn't have to when I reinflated mine from the 20psi I get sent out with.

I did have to drive around for a bit before the light went out tho'.

 

20psi is WAY too low

[Cyker]

9 minutes ago, Paul john said:

20psi is WAY too low

Correct!

[Haliotis]

System a bit disappointing when compared to our S.I.Ls Hyundai hybrid.  His has facility to check pressure in each individual tyre.

[Cyker]

My Yaris does that!   

But yeah it is a silly omission - I've always thought ever since they introduced Active TPMS sensors that you should be able to see the pressure of each wheel in the car's displays; It's mad that it's taken this long for it to actually be implemented, at least in the newer models, but better late than never I suppose!

[Haliotis]

Seems strange that a 2021 Yaris should have facility to check individual tyre pressures, yet a 2021 C-HR (reg June 2021) does not.  I thought the Dynamic was supposed to be well up in the range for accessories?

[philip42h]

21 minutes ago, Haliotis said:

Seems strange that a 2021 Yaris should have facility to check individual tyre pressures, yet a 2021 C-HR (reg June 2021) does not.  I thought the Dynamic was supposed to be well up in the range for accessories?

The Mk4 Yaris was launched in August 2020; the [Mk1] C-HR was launched in spring 2016. The original C-HR is a significantly older design (in car terms).

[philip42h]

15 hours ago, Haliotis said:

Does this mean that it is necessary to go through reset every time the light comes on?

I'm not sure that this question got answered (satisfactorily).

No, once correctly set, you do not need to, and should not, reset the TPWS system - it will remember the correct tyre pressure perfectly well.

But there is some [anecdotal] evidence of the TPWS warning level being set a little too high on initial delivery - maybe set high at the factory and not adjusted correctly by PDI. So, an owner may want to ensure that it is correctly set - I did ...

When resetting the TPWS you need to make absolutely certain that all four tyres are inflated to exactly the recommended pressure - and then go through the reset procedure. That way, you will get TPWS warnings on time and when you should rather than too early (irritating) or too late (potentially dangerous).

[Haliotis]

I haven’t found any clarity in the handbook, but does the warning light come on only when the pressure(s) are low, or does it also warn when the pressures are too high?

I have a RacingX pressure gauge, which is highly reviewed for accuracy.  Yesterday I checked my pressures and inflated the tyres to between 34 and 35 psi (spec is 33 psi).

The warning light stayed on, so I have reset it.  When it first came on, my pressures were actually 29-30 psi, so, if the warning light comes on again, hopefully the pressures will still be at around 32 psi.  I am happy with the pressures starting at a nominal 35 psi (cold).

[philip42h]

23 minutes ago, Haliotis said:

does the warning light come on only when the pressure(s) are low

The warning light comes on when the pressure drops below a certain percentage of the [re]set pressure - which is why it is rather important to set the pressure correctly before [re]setting the system.

[Cyker]

I don't think it comes on when too high - My tyres hit 48psi at one point during summer (Maybe last summer, I forget) when we were 5 up and full of gear, hauling donkey up the M40 one on a very hot day!!

And paul john don't even THINK about replying with "48psi is WAY too high!"

I KNOW!!!   

[Haliotis]

Just been on line and googled relationship of tyre pressure to temperature change.  The results were a whole string of websites with information - much of it being scientifically overloaded.   When inflating the tyres (theoretically from ‘cold’), the pressures can change depending on (a) ambient temperature at time of inflation. (b) change of ambient temperature during the day. (c) speed (d) amount of loading in vehicle.

Tyre pressure drop was given as approx 0.19 psi with every decrease of 1 degree Celsius.  There is actually a scientific equation for it!

The simple answer is that one should inflate from cold - i.e.,  when car has been standing and is at ambient temperature. From this point, tyre pressures will change depending on ambient temperature at any given time, how the car is loaded, prolonged high speeds, and road surface conditions.   This suggests to me that the old world method of checking tyres at least once a week is best, and that the warning light is only useful for detecting an abnormal pressure drop (picking up a nail, for example).

[Cyker]

It is quite interesting watching how much they fluctuate from driving, but for sure yeah the only time you can properly check the pressures is when they're cold; My old routine was usually a check on a saturday morning, but now I don't usually bother as I can see what the TPMS sensors say after a few minutes driving as they're still cold enough to show me if there's been loss vs. the desired pressure.

 

[Omegaseamaster]

I had the same issue recently as one of the tires had dropped to 26PSI. I put them all up to 33PSI and the warning light immediately turned of.

[Penfold72]

I has this when 2 of mine went faulty a week after delivery!!  Light normally goes out after a mile or so of driving without having to reset.

I was surprised when I found out there is no way to check individual pressures from the car, when it has the wireless sensors. Stupid omission IMHO

[Simone80]

AFAIK you can see it with some APP and an obd2 dongle

[Simone80]

but ok.. they should put it in the android application aswell..

[Cyker]

7 hours ago, Penfold72 said:

I has this when 2 of mine went faulty a week after delivery!!  Light normally goes out after a mile or so of driving without having to reset.

I was surprised when I found out there is no way to check individual pressures from the car, when it has the wireless sensors. Stupid omission IMHO

Yeah, I was pleasantly surprised the Mk4 Yaris had that ability, but I don't understand why it wasn't a feature in active TPMS cars from the introduction of the system, or at least the advent of multi-function displays!

 

[AndyRC]

Don’t forget to check for hidden nails/screws in tyres , we had a very slow puncture for a few  months which turned out to be a couple of screws ☹️