Originally Posted by Rhys
iansoutham
Read its not internal pressure.. THe ECU calcuates the rolling radiaus of the tyre, and any slight devation in rolling width it highlists puncture. This is what read on BMW's, im sure AlexF can confirm.
Only reason i know is mate has it on car, and always wondered how it worked, as there was no sensors going to the alloy/wheel etc.
It most likely is that on BMW (as I say, I do not know the systems well enough), but I have also seen the types where there is a band round the inside of the rim (narrowest point) which sends a signal to a transceiver box mounted elsewhere. I CANNOT confirm whether that is pressure (only assuming), again, it may be as you say with that method as well.