TPMS - When does the warning light illuminate?

[peternsomerset]

How exactly does TPMS monitor tyre pressure?

I am asking this as I bought my car via Skoda used car scheme which has a 30 day exchange!

After a couple of weeks getting to grips with driving a DSG and all the electronics I decided to check pressures which were all 1.85 bar instead of 2.5 bar.

After resetting I now have a dashboard rattle (stops when pressing between top right corner and top cover).  This seems to be a well known problem and the local dealer is investigating next week.  

I think the dealer may have reduced the pressure to stop the noise and would like to know what the pressure differential is to illuminate the warning light, is the a set percentage or actual value?

 

The dealer is supposed to have carried out a 100 point check before I bought it and I assume they checked the tyres!  There was over 26% drop in pressure and no pressure warning light but from an email to "sign in" next week it states I could be liable to costs which others have said are likely to be high.

I really like the car but the rattle is about 30mph and quite annoying.  I think this might well have been known to the retailer.  my very old Peugeot 307 had this problem and I cured it by wiping some silicone spray around plastic dash surround but am reluctant to do anything as the car is under PCP contract ATM.

Any info and advice as to what to do would be appreciated.

Thanks

[skomaz]

The TPMS system doesn't measure direct pressures, only the difference in pressures between tyres via the ABS sensors, so if all tyres are down on pressure by a similar amount it won't register an issue. 

 

I can't comment re the rattle but it's likely just two dash parts knocking together so maybe just needs some packing between them. 

[Ootohere]

@peternsomerseta pity you did you not check and set your own tyre pressures sooner rather than trust someone you do not know you or how you use the car set them?

Then reset the TPMS.

Check the spare if there is one, maybe over inflate so you can let down a bit if needed.

Check you can get the wheels off with the tools provided if needed. 

 

I hope you know the oil level as you got the car with a cold check, and at Normal Operating temp.  So you know the oil level is right.

Same with Coolant, check where it is now. 

Edited 27 January by Rooted

[Seasider]

The TPMS operates when there is a sudden deflation of a tyre compared with other tyres, so it doesn't monitor slow punctures, for instance, although it will spot the difference once the difference between the tyre with the slow puncture and the other three is noticeable.

 

The system isn't foolproof, however.  For example, I have had a cuple of false alarms which seem to be related to uneven road surfaces,  If this happens a number of times, ask the dealer to check the TPMS sensors settings.

 

Interesting about that little rattle as that appeared on my 2020 Fabia recently with 20,000 plus miles on the clock.  Intermittent and doesn't last long before disappearing.

[J.R.]

3 minutes ago, Seasider said:

so it doesn't monitor slow punctures, for instance,

 

It absolutely does, mine has been doing so for the last 3 years, after maybe 5 or 6 weeks I get the first warning which I reset with the button, I then visually kick test all the tyres and if I cannot detect any difference on the one with the bead leak I know I am OK till the next TPMS warning at which point I pump it up again.

 

The first warning is after a loss of maybe 5 or 6 psi, as I run mine at the higher load pressures it does not concern me, I always check and inflate if necessary before a long loaded journey.

[J.R.]

8 minutes ago, Seasider said:

The TPMS operates when there is a sudden deflation of a tyre compared with other tyres

 

8 minutes ago, Seasider said:

although it will spot the difference once the difference between the tyre with the slow puncture and the other three is noticeable

 

I had not appreciated you had written that proviso. That is not a sudden deflation, the system does detect slow punctures.

[Seasider]

3 hours ago, J.R. said:

 

 

I had not appreciated you had written that proviso. That is not a sudden deflation, the system does detect slow punctures.

But if I remember correctly, the instruction manual says it does not detect slow punctures.

[peternsomerset]

Thanks for the replies. 

I am a bit more wiser now and will try to get the dealer to say he had checked the tyre pressure when they did the 100 point checks!  If he does,  then I think either the service department or sales deliberately reduced the pressure to help quieten the rattle which has got a little better with the recent higher temperatures .

FWIW in reply to an earlier poster,  I have hardly driven the car since I bought it and checked water/oil in the first week of owning the car.  I am quite a practical person although a little ancient,  have rebuilt wet cylinder liner engines with paper gaskets and have some knowledge of engine oils and their use,  I also have recently replaced front struts on my old car to get it to pass its MOT!

 

[Routemaster1461]

Please bear in mind there are two types of TMPS. The direct type has pressure sensors in the tyres. This type will display the actual pressure in the diagram on the 'vehicle' page. This type will warn you if one tyre loses pressue, and will warn you wahen you start in the morning if a tyre has lost significant pressure overnight. I have never had a car with direct TPMS, so I don't know what sort of pressure loss will cause a warning. This type means that it is more diffecult to move wheels round as some system, maybe not all, require the sensors in the tyre to be in close proximity to a reciever near each wheel.

 

I suspect the Kamiq has an indirect system, as is fitted to my Karoq. This system, as stated, worksfrom the individual ABS sensors in each wheel. When first initiallised, the TPMS system learns how fast each wheel is rotating in comparison to the others. After it has done this, it continuously monitors for a wheel rotating outside the system limits. It can't be too sensitive, otherwise there would be a warning evry time the car went round a corner. In my experience a tyre needs to lose 5-8psi before a warning comes up. This type will not warn of a blow-out, or a flat tyre overnight as the car must be moving to register. If there is a fault in the system it may give an ABS warning as well. This system allows whells to be 'rotated' with no issues.

 

Restoring correct pressure without reinitiallising the system will not usually cancel the dash warning. 

[peternsomerset]

Thanks for the info,  I was not aware the effective pressure was calculated by  variation in circumference.  Just checked and  mine seems to be the same as your Karoq.

My main concern is that the dealer lowered the tyres significantly (27%) to help stop noise from the digital dash/black hard plastic surround.  There was and is no warning and I think it was reset at the lower pressure.  The problem is it may or may not cost me to put right as per other posts I have seen!

The car was bought on the Skoda Approved Car Scheme with a "100 Point Check" and did not get a report on what they actually did and I assume they checked/set the pressures. 

[nbramwel]

I recently bought a Karoq.  I checked the tyre pressures after a few days and found all were at 2 bar when they should have been at 2.5 bar.  I sorted this out myself.  I don't think the dealer deliberately deflated the tyres - the car was their demonstrator and had obviously not been looked after to my standards nor had they done their so called 100 point pre delivery checks.  I think this is typical of main dealers, not just Skoda ones.  They simply can't be trusted. 

[lastgasp]

I don't think that it's wise to make this into a big issue.  There has been a past thread on the subject of the recommended tyre pressure for the Kamiq - as displayed inside the filler flap.  I can't remember the figure - and I'm not going out in the dark and cold to take a look - but there was a consensus that the recommended pressure was unrealistically high (in the real world it cannot be an absolute number - there are innumerable individual variables that can affect it).  I have settled on 33psi as the figure that gives me a comfortable (i.e. not rattly) ride, good adhesion and no obviously undue wear.  Each individual car will be different dependant on usage, tyre make, loading etc.  It's largely a case of 'suck it and see'.

 

[peternsomerset]

I fully agree with you,  I took it in today mentioned the pressures and was diplomatic, they could not confirm if they had checked them and I agree 2.5 bar does seem a bit high. 

They did conform it was a bit "creaky" on a test run and there was also road sign error message,  I was told I could have it back later today but they were still working on it at 5pm. 

In my sort of twisted mind,  I am a little encouraged by that,  assuming it was actually worked on when I left it!