A déséquilibrage (whatever that is in English) detector.

 

It might have triggered if all 4 tyres continued their equal deflation, there is no other road speed indication to compare the wheel speeds to and the TPMS system has to cope with more than a 10psi variation when tyres are inflated to the laden settings.

 

Who knows?

 

5 hours ago, SteveTheElder said:

So, both disagree and agree...

Yes looking at what I wrote they were contradictory statements.

 

The truth is out there somewhere!

Edited 17 July, 20241 yr by J.R.

5 hours ago, J.R. said:

A déséquilibrage (whatever that is in English) detector.

 

 Yes, an 'imbalance' detector.

 

5 hours ago, J.R. said:

It might have triggered if all 4 tyres continued their equal deflation, there is no other road speed indication to compare the wheel speeds to and the TPMS system has to cope with more than a 10psi variation when tyres are inflated to the laden settings.

 

 

Prior to changing them, the old tyres they were pumped up for a full load, with TPMS set accordingly. The new tyres are inflated to 'normal' load so the rears were 10psi less.

 

Whilst I was initially frustrated that I couldn't reset the TPMS system/alert on the way home from the tyre depot, it does make a lot of sense for the system to be such that you have to stop and switch off - at least it creates the opportunity/impression that the driver has checked the tyres before resetting it.

8 hours ago, Gammyleg said:

Round about Christmas time I was a little tardy in checking my tyre pressures and left it for about 2 months before doing so. When I did get round to taking a look I noticed that all four tyres were running about 10psi below the usual 32psi which is where I set them. 

At no point did the TPMS warn of the low pressures presumably because the difference between each individual tyre at any one time was never more than the allowable tolerance.

 

So a puncture detector rather than a pressure gauge.

 

Indirect TPMS will only alert u if there is a rotational difference (equating to 4 psi or more) between all 4 tyres.

Indirect does not have a target tyre pressure like Direct TPMS.

Hence even if all 4 tyres r at 20 psi, no warnings or alerts.

If all 4 tyres r at 50 psi, no warnings.

If all 4 r at 30 psi, no warnings.

 

But if one of them is 20 psi, and the other 3 r at 30 psi, then u'll get warnings.

 

Direct TPMS on the other hand has a target pressure, and a sensor inside each tyre to measure the actual pressure.

Edited 17 July, 20241 yr by JR RS

4 tyres or pairs of 2 do not need to be set at the same pressure so the tyres having the same circumference.  You can set at what you want and the car registers.  You can put on an odd 1 out SPARE of a slightly different size / circumference, reset the TPMS and in many VW group cars just carry on with no warnings.  Some will have some functions disabled.  But then using CC or ACC with an emergency spare on of a different size, weight, tyres compound / type is not Simply Clever.