01-13-2014, 10:39 PM | #1 |
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Okay, how does the tpms ACTUALLY work?
I've been following some discussion on the matter here, but a line in the 'BMW X1 Quick Reference Guide' caught my attention.
Page 29 says specifically: "The system identifies a loss of pressure by comparing the speeds of rotation of the individual wheels as the car is traveling." Other references seem to indicate that there is some electronic component in the wheel. So which is it; electronic sensors or tire rotation? When buying replacement wheels (for winter tires, for instance) is it necessary to buy wheels with sensors? A really handy feature of our A4 Audi is the ability to install the winters here at home, with no need for the dealer to reset for the replacements; tire rotation alone keeps you informed if there is a tire down. Help me out here, and thanks, Moon |
01-13-2014, 10:48 PM | #2 |
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There are tire pressure monitors (electronic sensors) in the wheel.
I know this because I paid like $600 to get brand new sensors and valve stems on my aftermarket tires and wheels. And then I had a flat with one tire, and the sensor indicated that "The front right tire pressure is low", and was stuck on the side of the road in the middle of nowhere during a snow storm. You would need the either reuse your stock TPMS sensors on new wheels, or get new sensors. But you will need it, or the light on the dash will indicate there is an error with the TPMS. |
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01-13-2014, 11:02 PM | #3 |
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Most (all?) models BMW sells in the USA use TPMS in the wheel. In some other markets, they use the computer and the tire rotation variances to detect if a tire is going flat. The TPMS with sensors is a more accurate alert to a slow air leak than the version that uses variances in tire rotation rates, as with a RFT, it has to lose a lot of pressure before it starts to sag much. The sensor in the wheel will alert much sooner, but if it is a big leak, that point may be mute.
Our user manual tends to show both USA and Canada option descriptions...make sure you are reading the section for the USA. You can probably tell if you look at the filler valve...most of the time they use a rubber fill valve only if it uses the tire rotation...the valve stem with TPMS in the wheel, use a metal stem. |
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01-14-2014, 08:49 AM | #4 |
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There's a nut on the stem of my tire stems; I'm taking that to mean that I've got some electronic component in the stem.
Okay, two questions, one of which seems to have already been answered ($600); the other being, can the owner reset when he changes rims fall/spring? Using the standard re-initializing directions in the manual, or some other means? Thanks, Moon ETA- squish, thnx, and I'm a pretty relentless tire pressure checker, but then I do have a garage.... M |
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01-14-2014, 08:55 AM | #5 |
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tpms sensor can be bought at ebay either used or new for fair price oem.
some aftermarkets sensor are compatible with bmw systems. yes u can reset tmps thru the menus on the screen or the stalk on the steering wheel |
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01-14-2014, 10:34 AM | #6 |
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IIRC, the TPMS sensors with my Winter wheel tire package from TireRack cost ~ $250 total
I never have to reset the TPMS display when I change from OEM wheels to T-Rack winter set.
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01-14-2014, 11:34 AM | #7 | |
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Quote:
We tolerated the yellow warning light in the Focus (my daughter is still tolerating it..) mostly because of the hassle of taking the car to the dealer to get it reset spring and fall. Best, Moon |
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01-14-2014, 03:21 PM | #8 |
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There are two TPMS warning lights. One is the big warning light in the center of the dash display that tells you something is wrong, the other is a tiny yellow icon in the upper part of the dash that indicates the system is off.
When I put my non-TPMS snow tires on last week I pulled the fuse for the TPMS, started the car and followed the reset instructions and now the only light that comes on is the little one on top which says the system is off. It is the same type of light you see if the ESC is deactivated, which I do if I want to do donuts in the snow (RWD is so much fun). It appears as though you do not have to reset the TPMS every time you start the car which is nice. I can live with that. So that is a nice option for folks who like myself are only putting the snows on for three months or thereabout. The other option is to deactivate the TPMS by recoding but this requires changing the Vehicle Order or VO. That will get rid of all the warning lights. My understanding is that is not a wise thing to do because the dealership will have to undo that to do any repairs on your car that require tapping into the cars computer. |
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01-14-2014, 05:03 PM | #9 |
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It's my understanding that the TPMS have a unique ID code, sort of like that in an Ethernet adapter...i.e., unique to that sensor. To get the car to recognize it as one of its own, and not from some adjacent vehicle, you need to go through the reset procedure. Once that is done, it remembers those values, and will only respond to those sensors, not someone you may be passing on the highway.
On the BMW, at least my model, it takes a short distance before the computer gets a chance to 'hear' from each sensor and report it. It does not light the fault light until it has tried, and failed to find ALL of them. If it finds some, but fails to find all of them, it declares a system failure. If it never finds any, it tends to only light the light, not generate an error message. The things have a battery in them to power the transmitter. They also have a motion sensor that shuts them down when the vehicle has stopped. |
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01-14-2014, 07:46 PM | #10 |
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I ordered sensors from TireRack when I ordered my winter wheel/title set from them. IiRC they were less than $250. It was something like $200 for the sensors and then a little extra for the valve stems. You don't need the sensors but you'll see the yellow light up on the console.
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