Not sure how the Tyre Pressure Loss Indicator works (anyone know - I thought it was to go with road height?)), but it worked ok on the dual carriageway today.

Pulled over when the car came up with a warning and couldn't see anything wrong with the tyre (luckly as my ex demo doesn't have spare!), so gingerly headed back to the office - look at tyre again, couldnt see anything / feel it was low.

But popped to tyre place down the road just in case and turns out there was a screw in the tyre - was repairable, but without taking the wheel off I''d not have found it probably unless the TPLI picked it up as it did - guessing it's fairly sensitive ?

It works off the abs sensor. Once set it will have a set number of pulses for a set distance it this varies outside its given tolerance it will set off the system

Yep the ABS sensors basically calculate the rolling circumference of each wheel when told to calibrate (after selecting the set option, takes a mile or so for the calibration to complete).

Once calibrated if that rolling circumference changes my any significant margin (I believe either way) it will alarm. The good thing with the system on the O3 is that it indicates which tyre/s are affected....previous iterations would flag a problem but leaving you to work out where there was a problem.

Different to the systems that employ wireless valve sensors that actually report the tyres individual sensors back to the ECU and alarm if the actual pressures change within certain limits...the O3 system obviously has no awareness of actual tyre pressure.

Thanks guys useful to know as if heard some cars you could swap wheels around as it confuses things.

The only other time the TPLI gas gone off is when I was driving through some road works on the M5 with narrow lanes and I probably got 'stuck' driving over a few hundred yards of cats eyes - guess this temporarily changed the rolling circumference.

It certainly works better than my eye / tyre kicking judgement anyway!