For the 2nd time in 5mths[new ownership] the display warned of low tyre pressure & on checking there was NO loss of pressure in any tyre, I DO check all the tyre pressures weekly with NO adjustments needed [cold tyres] wondering if the sensors/connections are "weathered" & need a clean up..so remove wheels & locate but where are they ? OR should I just go to the dealer & have a check done under warranty ?

11 minutes ago, BACUPIAN said:

For the 2nd time in 5mths[new ownership] the display warned of low tyre pressure & on checking there was NO loss of pressure in any tyre, I DO check all the tyre pressures weekly with NO adjustments needed [cold tyres] wondering if the sensors/connections are "weathered" & need a clean up..so remove wheels & locate but where are they ? OR should I just go to the dealer & have a check done under warranty ?

There are no sensors in the wheels, the TPMS uses the wheel speed sensors and some trick software in the ABS controller.

Edited 5 April, 20197 yr by PetrolDave

When you check the tyre pressures cold do you then reset the TPMS?

When there is a warning and the tyres are hot do you check the pressures and see what they are and that a wheel / tyre is not getting hot due to a binding brake?

I've had my TPMS trigger once in the year I've owned it, I was in slow traffic on the M25, laden with enough stuff to keep the wife and 2 kids happy for 3 nights in Wales where we were staying for a friend's wedding.

 

I moved over as far as I could get to see how far the traffic was slow for and spent a little time on the rumble strip, after a few seconds the TPMS flagged up the rear O/S tyre had low pressure.  I checked it later and it was fine.

 

All I can think is that the rumble strip made the car think the wheel was turning faster than it actually which was enough for it to think the tyre was down on pressure.

Could the air that escapes when checking the pressures be enough to set off the monitoring system?

If enough air lost, or a little air each time, but should make no difference if you reset the TPMS having checked the pressures.

The system just knows the circumference of the tyre has changed.

This is why i mentioned the brakes binding on a corner, that can change a pressure, same as if you track your car and a front wheel / tyre heats more than on the other side.

1 hour ago, Skoffski said:

If enough air lost, or a little air each time, but should make no difference if you reset the TPMS having checked the pressures.

I suspect many (most?) people don't do that.

A colleague is have lots of problems with his Volvo system too (also ABS based).

Many people never read owners manuals, or if they do do not take in what is written.

TPMS require setting.

Even Tyre Fitters or Dealership Fitters and Techs might not bother Resetting TPMS after putting air in or letting out air.

I had the warning flash up within the first month, on it's first long trip coming home from The Lakes on the M6. Stopped at the first services (luckily only a couple of miles) checked all wheels for heat and tyres for pressure, all were fine, had a comfort break and checked again (new car paranoia). 

It's not flashed up since - that's tempted fate....

Mrs Cakemonster's 1 series BMW throws a wobbly every couple of months with the tyre pressures (it knows the actual pressure in kpa, so possibly a different system)

Basically, I think they're the sort of systems that are more trouble than they're worth, they don't detect very slow leaks and a catastrophic loss is usually self evident - speaks from experience. 

They're no replacement for a mk1 eyeball and a gauge. 

Even false alarm occurs much too rare comparing how often you should actually check the pressures. It doesn't work on circumference principle, but on torsional resonance. Not perfect, but good enough, saved two of my tires so far. 

it is affected by the road quality and air temperature, so not bad checking the tires more frequently (not only visually, but on the gas station or personally with the correct instrument) and resetting the system afterwards.

20 minutes ago, nidza said:

 It doesn't work on circumference principle, but on torsional resonance.

 

Not kidding actually. If there are tech savvy people in the thread, we can discuss this super clever design once again. 

 

System is able to detect simultaneous loss of exact same amount of air of all 4 tires, which couldn't be possible with circumference only based concept.  

 

Are you referring to the Skoda system that uses the ABS sensors?

 

Torsional resistance?

 

@nidza

If you go to your car and let all 4 tyres pressure down equally by 5 psi you will see that it does not recognise the difference.

@J.R. Resonance.  

 

@Skoffski, please wait, stay tuned (check the pic below).

 

It actually raised my interest when on sudden drop down of temperature (20 degrees since day before), Škoda alarmed loss of pressure of all 4 tires. I was confused how this is possible, if it matches circumference of the wheels, and all 4 wheels still have exactly the same, reduced slightly since the day before. Then I started Googling to cure my curiosity.  

 

 

Still interested, shall I continue?

Lovely, but then i can check my own cars, i have had a few Skoda.

Changed a few tyres and wheels over the years... Reset a few TPMS's.

Edited 5 April, 20197 yr by Skoffski

Nidza, resistance was a typo, I have dyslexia between the brain and fingers!

 

Still have no idea what torsional resonance is though or how the ABS sensors could measure it.

 

The warning that you show above is one that for safetys sake I would expect to be displayed after a detected wheel RPM imbalance (percieved by the system to be underinflated tyre) for one or more tyres, it makes total sense that all 4  tyre pressures should be checked, you dont show the warning saying that all 4 were underinflated.

 

If the vehicle has a GPS built in to the electronics then its plausible that a system could detect a change in the wheel RPMs and the actual road speed, without that in the circumstances that you describe, the 20°c temperature drop (which I dont actually think would change the rolling radius enough anyway) the vehicle would see all 4 wheels rotating at the same RPMs or within operating parameters as the day before and display the same speed which would be (IMO) an imperceptible over-indication.

Edited 5 April, 20197 yr by J.R.

In fact dont some of the early systems just display that one or more tyres are under-inflated without specifying which?

It needs to be the TPLI+ indirect system (as opposed to just TPLI)  in order to do the 'multiple tyres simultaneously' detection. Not sure what the PR code is for this, but I suspect it's not necessarily fitted to all models. The SSP on the subject is quite interesting.

Exec summary:

Tyres have a 'natural frequency of vibration' according to their physical properties and operating conditions including inflation pressure.

The ABS sensors are more sensitive than the normal ones in order to pick up slight timing differences between the pulses, so as to pick up the vibration patterns.

Clever software learns these vibration patterns (frequency and amplitude) over a range of driving conditions during the adaptation phase after a reset. Once complete, it detects variations of sufficient magnitude away from these learnt norms, and flags up problems as it sees them.  Including equal loss of pressure from all wheels.

 

So they claim anyway.

 

In the OP's case, I guess something like the loss of a wheel balancing weight could possibly affect this system?

Edited 5 April, 20197 yr by Wino

Good to know, so they are not wheel speed sensors but vibration sensors?

 

I get the "resonance" now but not the "torsional".

 

Glad I dont have any of this rubbish, I had been considering retro-fitting the TPMS reset button and enabling the feature, I wont bother now.

 

If this car proves to be unreliable, and so far all its ills have been electronic then I am either going to go back to as good a  MK1 Octavia as I can find or something from a decade before that.

Wheel speed and wheel vibration (very small variations of wheel speed within single rotations).

Vibration is torsional, in the axle of rotation. Tire is elastic and it vibrates according its stiffness, ie inflation pressure. That's the catch, but the correct wording is torsional resonance frequency and it is a mechanism which evaluates each of the wheels independently. Plus, all of them at once, if they suddenly loose the pressure. 

 

When learned frequency pattern changes, system alarms. 

 

While wheel rotates it seems to be pretty efficient. What it can't do is to alarm you if tire pressure is lost while parked. You can easily destroy the tire if you don't make visual check before you start driving...

 

If it is circumference only, you would never need to calibrate the system, but you do. Then it starts learning each wheel independently. They say 20 minutes of normal driving is enough. 

Good that some basic cars come with the basic system as was there for Run Flat Tyres.

You can put on a Spare wheel and reset the TPMS and have no warning.

Fit Snow Socks on the Drive Wheels or even chains, switch off TC and not reset the TPMS and still get no warning.

 

There is the various CC and more advance systems that when you fit a spare wheel the systems are inhibited.

My other car was built before TPMS because compulsory in the EU so I'm using this system that monitors the pressure in each tyre using adapters screwed onto the valves

Tyre Dog

Thanks for ALL of your replies & I am inclined to think it is probably a "heat related" issue & will still check ALL tyre pressures when cold & will always re set the tpms !