I'm curious, apparently the DDS works by using the ABS sensors on the wheels to detect when one is spinning quicker than it was and is therefore losing pressure which makes sense, but I can't see how storing the pressures actually works. The car has to be stationary to store them (I tried doing it while moving earlier and it failed), so what does this actually do?! Does it just reset something so the car learns over time how quick each wheel spins or something? It also begs the question why doesn't it keep flagging low pressures when you go round corners and the wheels change speed? It would make more sense if you had to store them while in motion in a straight line so it could compare speeds, but I guess that's dangerous having to interact with things while moving!

I think it works by measuring the wheel circumference rather than the speed.

The ABS module determines the loss of pressure in the tires by calculation using the wheel speed sensors of the ABS system. If a tire loses pressure, its diameter decreases and the speed of the wheel therefore increases.

If the ABS module detects such a loss in pressure, it sends a signal to the instrument cluster via the CAN bus and a warning message is displayed in the driver information system. The warning threshold depends among other things on the dimension of the tires being used, the vehicle operating conditions and the status at the last initialization.

Since neither the absolute tire pressure nor the position of the tire is known, after a tire pressure warning the pressure of all the tires must be checked and the system re-initialized. If necessary, the cause of the loss of pressure must be investigated.

I didn't think the fiesta works via a canbus system?

But yeah, as above it calculates via the wheel speed.

This is how the tire pressure monitoring system (TPMS) works on the fiesta

https://app.box.com/s/qyhihtw0vnk3iwffk0je

It also begs the question why doesn't it keep flagging low pressures when you go round corners and the wheels change speed?

Good question

Sent from my GT-I9300 using Ford OC mobile app

This is how the tire pressure monitoring system (TPMS) works on the fiesta

https://app.box.com/s/qyhihtw0vnk3iwffk0je

Good post, thanks :)

hmm that says each wheel has an actual pressure monitoring sensor in it. As above I didn't think the Fiesta did?!