"Measuring tyre pressures…………………….."

Since I've had the car - I've only managed to see the tyre pressures displayed on one occasion.

Normally, if I select "Vehicle Status" on iDrive - it just reads "measuring tyre pressures" and gets no further.

Am I doing something stupid?

Hi, the system will only measure tyre pressure when driving, it pauses measuring when standing still. When you start to drive again, it will continue calibrating. After about 10 min. of driving, the calibration should be done. I did this once up to now and was a bit puzzled as well. But it is in the manual I presume. Hope this helps!

Have done that several times and always worked without problem. Needs a few minutes. It will also give me a result when I am standing still after several minutes of driving. Pressure is higher when the tyres are warm.

Frank

If you cannot get the pressure to display, you may need to first prep the tires to the proper specifications, then hit the reset. Once you've done that, the system should remember the sensors, and produce a readout within a mile or so of travel. To keep the sensor's battery from discharging too fast, they shut down when stationary, and it takes a few revolutions to wake them up, but then, they only send out a signal maybe once every 30-seconds or so. So, it is not instantaneous until they sync up.

Does anyone know where exactly the sensors are and how long the batteries will work?
What do I have to pay attention for when I change the tires? Do I need new sensors? Do I have to tell the dealer not to change the valves (if the sensors are inide them?

I couldn't find anything in the manual...

I think you will find there is a sticker on the wheel adjacent to the valve which appears to be a radio frequency warning.

Can't imagine any reason why the i3 sensors should differ from other BMW models and there is a blow up of the sensor/valve assembly on this eBay ad

http://www.ebay.co.uk/itm/BMW-3-Series-TPMS-Tyre-Pressure-Sensor-Valve-Repair-Kit-/251147132281?_trksid=p2054897.l4275#ht_8804wt_1190

When changing the tire, you should replace the stem...the actual sensor screws or bolts to the stem, and they are meant to be easily separated. The batteries are not replaceable (as far as I've seen), so when the sensor eventually dies, you'll need new ones. The reason to replace the stem is that the O-rings that create the seal can and do get hard and can crack...a new stem gives you a new valve and seals. Also, the stem can become corroded, and begin to look bad. As an aside, you can get new stems in various finishes and colors, so you could swap them to complement or update the look (say in chrome or black, or red, for example).