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Discussion Starter #1
Rotated my tires on the X1 today and wondered about something. Maybe someone on Bimmerfest has experience with this. I swapped the front tires to the rear and rear to the front. My question is - How does the TPM system know where the individual wheels are located? Or do they even need to know? When I do a TPM reset does that identify which location each wheel is at? Here is the situation - if the front right tire is low on pressure and I have relocated that wheel to the right rear (no reset of TPM), will the TPM know its at the rear or will it still think its at the front? Am I the only one to ever have consternated over this? By the way I am accustomed to my Audi which does not have pressure sensors within the wheels, rather it evaluates tire rotation speeds to determine low pressure.
 

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'17 X1 - Rooster Cruisin'
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Are you sure that you actual have TPMS system on that X1. I think we have indirect monitoring via the ABS system. If a tire's pressure is low, it will roll at a different wheel speed than the other tires. This information is detected by your car's computer system and interpreted as a possible low pressure indication irregardless where the tire was previously. Btw, ever notice that you have to be moving for a period of time before the computer gives a refreshed reading of the tires current pressure? Stick with an accurate tire gauge to know for sure.
 

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Discussion Starter #3
If you look at the tire valve stems you can tell if there are pressure monitors mounted inside by the rigid steel valves. That should answer your statement about X1s having indirect systems. Ours also read psi pressures, an indirect system does not know pressures within a tire.

Just to reiterate what I am looking for: its how does a direct TPM system register a wheel to a position on the vehicle? What is the technology that handles this?
 

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'17 X1 - Rooster Cruisin'
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Colpa mia...I stand corrected. My X1 does have the metal valve stems and page 109 of the owners manual states that the sensors in the tire valves measure tire inflation pressure. Page 110 explains why and how to reset the monitoring system (TPM) after an adjustment of the tire pressure after every tire or wheel change. Thanks - the more you know :thumbup:
 

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(I guess) there's a receiver near each wheel that picks up the closest and strongest signal. The metal in the car body would also shield each receiver from other three transmitters. If the pressures are different front to back, you might get an low pressure message after rotation, corrected by resetting the TPMS.

When a bunch of Porsche 911's are line up next to each other they often read the tire pressures of the car's sitting next to them.
 

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02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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TPMS identified individual transmitter location by time differences among the signals.
 

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TPMS identified individual transmitter location by time differences among the signals.
That would require an interrogation ping sent from the central receiver to the sensors. That would require that the wheel sensors also have a receiver in addition to a transmitter. They apparently don't have receivers in them.

Here's a blurb I found on a Jeep forum, where the Jeep Bubba copied a description from a Jeep tech' manual or electronic tech manual. It says that there are three receivers in wheel wells, and the computer can figure out by default where the fourth wheel is located.

https://www.wranglerforum.com/f274/2013-tpms-how-it-works-1570105.html


The Premium TPMS determines the location of the tire pressure sensors by using transponders located in three of the four wheel wells on the vehicle. A fourth transponder is not necessary in the remaining wheel well due to the process of elimination theory. Once the system knows the location of the first three sensors, it assumes the location of the fourth tire pressure sensor, and updates the graphic display when necessary. For more information, (Refer to 22 - TIRES/WHEELS/TIRE PRESSURE MONITORING/TRANSPONDER - OPERATION).



So, I guess I was 75% right. :p
 

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Discussion Starter #8
Thanks guys, your input was very helpful and I now have a good idea how these TPM systems function in terms of registering position of each wheel.
 

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If you look at the tire valve stems you can tell if there are pressure monitors mounted inside by the rigid steel valves. That should answer your statement about X1s having indirect systems. Ours also read psi pressures, an indirect system does not know pressures within a tire.

Just to reiterate what I am looking for: its how does a direct TPM system register a wheel to a position on the vehicle? What is the technology that handles this?
Hi
[A you have the metal tyre valve stems you have bmw TPMS sensors in each tyre which provide pressure and temp readings. You already know a signal is sent and received.] After you have rotated your tyres you will need to inflate them to correct pressure for new position then go into idrive and use the tyre pressure re-set function. It will require you to drive the car whilst it measures the pressures, this calibration will also confirm location of each sensor on the car Effectively registering the sensors with new tyre location.
Mark
 

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Discussion Starter #10
Thanks MJE60 for your input. I probably did not word my original post optimally but what I wanted to understand was not how to rotate tires or adjust pressures but simply how the TPM system would know when a wheel***8217;s mounting location was changed. I.E. if the wheel from FR is moved to RR how does the system understand that and what technology does the system use for that piece of the puzzle?
 

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Wikipedia's page on TPMS says that some TPMS systems determine which signal is from which wheel based on signal strength, and signal strength is based on distance between the TPMS sensors in the wheels and the receiver. Wiki' also says that some TPMS wheel sensors have a low-frequency (also low power) receivers to accept commands to transmit data (pressure, temperature, ID code, battery status).

https://en.wikipedia.org/wiki/Tire-pressure_monitoring_system


For my F10, the bootleg BMW on-line service manual (NewTIS) says that the control unit transmits commands to the wheel sensors via a 125 kHz signal (low-frequency), and that the wheel sensors transmit back their data at 433 MHz (ultra-high-frequency). NewTIS says that there are low-frequency "transmitters" (plural). So, there's one for each wheel and each wheel sensor only receives the command signal from the transmitter nearest to it. The low frequency transmitters are controlled by the control unit, and would presumably query each wheel sensor separately, commanding it to transmit its data.

https://www.newtis.info/tisv2/a/en/...nts-with-a/a66-tyre-pressure-monitor/48JmM7Lz


It looks like BMW TPMS's control unit is located to the left side of the car near the rear bumper on my F10.

https://www.newtis.info/tisv2/a/en/...nts-with-a/a66-tyre-pressure-monitor/GPZEuTI1

Here's a systems diagram of the TPMS for an F10. The big box in the middle is the control unit. The smaller boxes A6, A7, A8, and A9 are the low-frequency transmitters for each wheel. The remaining small box, A10, is the high-frequency aerial that receives the data from the wheel sensors.

https://www.newtis.info/tisv2/a/en/...s-with-a/a66-tyre-pressure-monitor/1VnYxObBvb
 

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Additional info from the newtis.info website in regards to how the TPMS works and detects the location of each tire when you have the direct (RDC) monitoring system:










 

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Discussion Starter #13
Qsilver7, you hit the nail on the head. This is exactly the document we needed to understand the theory and function of the TPM system. Thanks very much.
 

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:thumbup:
 
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