When does TPMS read pressure? - BMW X5 Forum (G05)

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There's a battery in each TPMS. If it broadcast constantly, the battery would not last very long. They also have a motion sensor, and once you start moving, they only broadcast about once each 30-seconds in a burst. The timing of when each TPMS occurs is then used with the rotation sensors to try to figure out where each TPMS is. As you go around a curve or corner, each wheel will rotate at different speeds, so travels a different distance. After time, this allows the vehicle to figure out where each sensor is located. If you were to drive in figure 8's, it would figure it out faster, but normal driving is enough often, within a mile or so, maybe sooner. Older vehicles tended to use a receiver for each wheel, but BMW and others, now generally only use one, so that is why you have to drive to figure that out. An alternative would be to pick up a TMPS tester. That sends a strong enough signal to the TPMS when it is close to trigger it to send data. It also can read the battery status, so you can tell when the thing is going to need to be replaced. Some older ones required you to use an included big magnet to trigger the TPMS, but the ones BMW uses do not. I'm guessing, those use a small steel ball that moves when the wheel is rotating, and that is sensed (maybe by a Hall effect sensor), and the magnet moves the ball. Unless you rotate or change the wheel locations, the computer just looks for the ID, and already knows where each one is, so the readout is faster.

Each TPMS sends out a set of data:
- ID, sort of like an IP address
- temperature
- pressure
- battery status

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