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Discussion Starter #1
How do the tyre pressure sensors actually work ?


My son reckons it's to do with a sensor calculating the rotation of the wheel, so if the pressure drops the rotation alters ?
I thought it was a sensor in the actual valve ?


Reason for asking is that I recently had a puncture that was repaired and the tyre shop changed the valve at the same time, which I didnt realise at the time.
I did have to reset the tyre pressure monitor within the car and all seems ok.
But this got me thinking that theres no way the tyre repairer would put a sensor type valve back on the car ?
So how do these pressure monitors actually work, is it on the valve or as my son seems to think sensors monitoring the wheels rotation ?
 

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How do the tyre pressure sensors actually work ?


My son reckons it's to do with a sensor calculating the rotation of the wheel, so if the pressure drops the rotation alters ?
I thought it was a sensor in the actual valve ?


Reason for asking is that I recently had a puncture that was repaired and the tyre shop changed the valve at the same time, which I didnt realise at the time.
I did have to reset the tyre pressure monitor within the car and all seems ok.
But this got me thinking that theres no way the tyre repairer would put a sensor type valve back on the car ?
So how do these pressure monitors actually work, is it on the valve or as my son seems to think sensors monitoring the wheels rotation ?
You are both correct.
The earlier V40's used the special valves that detect loss of pressure - quite expensive - plus were unreliable, so Volvo ditched them.
My previous V40 2014 did not have any version of TMS fitted, but I think it became compulsory on all new cars 2015 sometime.
The later models used standard valves, with some wheel rotation sensor(s) on the car.
 

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Discussion Starter #3
Cheers Stu,
So I guess my 2016 V40 would have the non-valve type ?
 

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I have this fitted in my current car (Seat Ibiza), previous car, (Seat Leon). Oh, btw...I pick up my new V40 in 10 days time!

And yes they measured if rotation was 'off.' I had the device ping up thrice in 4 years, 2 were correct, with one wheel (mine didn't tell me which wheel), having lost pressure due to slow puncture. The one time it was wrong, was when I was driving on light dusted snow, perhaps more wheelspin than usual, so it pinged up.. But everytime I add pressure to tyres, I would re-set them....
 

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Cheers Stu,
So I guess my 2016 V40 would have the non-valve type ?
Yes, the active valve stem pressure sensor TPMS was ditched in the MY14.5 update for the passive system that looks for variances in wheel RPM using the ABS sensors.
 

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I'm not sure which mine has, but it is very sensitive to temperature.


On Sunday night the I started getting warnings from the nearside front that the pressure was low whilst driving through the Cairngorms and the temperature dropped to -4. About 10 minutes later I got a warning that the offside front was also low, followed minutes later by both rears.


I recalibrated, and the two rear tyres went back to normal, and then the next morning recalibrated again when the temperature was more normal. This then showed the offside front as being fine as well.


After work I drove to the garage to check all the pressures. On the way there the nearside front also went back to green.


Checking the pressures at the air pump, and they were all the same!!
 

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That's the water vapour content of the air in the tyres condensing in the cold and lowering the pressure. It's why on racing and performance cars they fill the tyres with nitrogen to help keep the tyre pressures stable under extreme temperatures.
 

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This Nitrogen fad is all a con. All gases expand in the same way with temperature, unless they're at the boiling point (or triple point depending on temperature) of the underlying liquid/solid.
Air is almost 80% Nitrogen anyway, did you know that folks?


There is a "slight" difference in the porosity of tyre materials that means, over a LONG time, the Oxygen leaks out quicker. But surely if filled with air (78% Nitrogen) that would be a good thing if Nitrogen is good?


The only significant factor (hinted at by buzby) is the presence of water vapour, messing things up. The Nitrogen supplied is usually "dry" and fairly pure. Air, compressed by a pump at your local garage or tyre place, has significant quantities of water vapour, depending on the weather. Though even then it's at most about 4% so can affect tyre pressures only by a pound or so.
Probably best to pump your tyres up with air on a cold dry February day and save the Nitrogen con tax ...… :grin2:


If you're racing and looking at tiny marginal gains, then yes use DRY Nitrogen. Otherwise it's a waste of time.
 
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I'm not sure which mine has, but it is very sensitive to temperature.


On Sunday night the I started getting warnings from the nearside front that the pressure was low whilst driving through the Cairngorms and the temperature dropped to -4. About 10 minutes later I got a warning that the offside front was also low, followed minutes later by both rears.


I recalibrated, and the two rear tyres went back to normal, and then the next morning recalibrated again when the temperature was more normal. This then showed the offside front as being fine as well.


After work I drove to the garage to check all the pressures. On the way there the nearside front also went back to green.


Checking the pressures at the air pump, and they were all the same!!
I have the same problem, being afflicted every now and then with false alarms. When I measure the allegedly lower pressure, it is exactly the same as that of the OK tyre on the other side. Really wish it wouldn't...
 

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Had this same issue today which is why I'm here on the forum. All 4 tyres showing amber today outside temp 3c. Checked all tyres with my plug in tyre inflator and all OK, tried recalibrating twice but to no avail all still amber. Went to a service station switched engine off used their inflator recalibrated and all went green over the next few minutes. Alot of fuss over nothing but still worth having as it did detect a slow puncture a few months ago due to a nail.
 

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I have the same problem, being afflicted every now and then with false alarms. When I measure the allegedly lower pressure, it is exactly the same as that of the OK tyre on the other side. Really wish it wouldn't...
P.S. The boy who cried "Wolf!" Last Sunday, I came around a corner on a road crossing the Jura to find that a rock had fallen from the slope and broken on the road. I avoided all the big bits, but then a bit later, the car informed me that the right front was low in pressure. My immediate reaction was "Oh no, not again!" and I ignored it. Moreover the car still felt fine (I am not a fast driver).When I got home (not too far from where I'd encountered the stone), I found that the front right had a damaged sidewall and was nearly flat! So, all I got for Christmas is my two front tyres. And I'll pay more attention next time.
 

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I’ve just had my 2016 T2 a couple months, TMS can on while parked yesterday saying rear right Tyre was low, shocked at the garage it was 30psi but the rear left was 27psi! Why would it pick up the higher of the two?
 

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Great thread guys...! Especially the first appearance of the term ‘triple point’ wrt gases.
 

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How do the tyre pressure sensors actually work ?


My son reckons it's to do with a sensor calculating the rotation of the wheel, so if the pressure drops the rotation alters ?
I thought it was a sensor in the actual valve ?


Reason for asking is that I recently had a puncture that was repaired and the tyre shop changed the valve at the same time, which I didnt realise at the time.
I did have to reset the tyre pressure monitor within the car and all seems ok.
But this got me thinking that theres no way the tyre repairer would put a sensor type valve back on the car ?
So how do these pressure monitors actually work, is it on the valve or as my son seems to think sensors monitoring the wheels rotation ?
Your son is rite it works by using the abs system measuring the turn of the wheel a soft or flat tyre takes longer to make a full turn .... no expensive tyre pressure monitor
 

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How can I tell if I have TPMS (in my late 2016 D3 Inscription)? in the MY CAR it does not offer me the option to recalibrate my tyre pressures. I can find it but it's greyed out.
 

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See #2 Self Recalibration should now be on all versions post 2014, and should not be greyed out.
 

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Maybe the tyre pressure system needs a service - one of the 3 error codes
 
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