Tyre Pressure Monitor Accuracy


Registered User
I have the tyre pressure monitor on the car. A few weeks ago I blew the tyres up to the higher of the two pressures on the door sticker (42psi in my case), and reset the monitor on the MMI. I've not used the car a huge amount since then for various reasons, nor have I checked the pressures. Finally did them today and was surprised to discover they had all dropped to between 34 and 38psi, with no warning from the monitor. In both cases the pressures were checked with my own compressor which I believe is accurate.

Now, I admit I am at fault for not checking the tyres more frequently, but that said I would have expected the monitor to have picked up a drop in pressure of this magnitude. Does anyone know any more about the technical aspects of these systems; how accurate are they? I get the impression their only use is to give you a bit more warning of a tyre that's about to blow out; still useful, but not quite what I was hoping for.


Registered User
I think it measures differential in circumference. If they all fall the same amount, it won't be detected. Only when one is out from the others - at least that is how I understand it....


Registered User
Hi, as far as I understand it uses the ABS and detects the difference in rotational speed of each wheel.


Registered User
Worked fine for me and alerted me when mine had dropped by a few PSI


Have found it pretty good on 4 Audis we've owned (not an 8V yet). BUT Very annoying when it alerts you that there is an issue at 0500hrs when it is wet and cold and the only problem is a 2psi difference on one wheel.


Registered User
I trust you had run the car before checking the tyre pressures, if so I would suggest you purchase a digital pressure gauge as this will be your constant monitor.