TPMS? Passive or Active system?

On the new 2009 335i, is there actually sensors inside each wheel or is it a passive system like some cars where it just compares rotation to other tires?

sensors in the valve stems.

Active. Sensors are in the valve stem.

Actual sensors in each wheel. Sedans prior march 2007 build had the passive system

Both! I know the car keeps track of the sensors. (Did a bit of an experiment. Worked beauifully.) And I'm pretty sure the car still keeps track of wheel rpms.

Originally Posted by ProfessorCook

Both! I know the car keeps track of the sensors. (Did a bit of an experiment. Worked beauifully.) And I'm pretty sure the car still keeps track of wheel rpms.

Both? Yes and no, and not maybe. (How's that for narrowing it down?)
Yes because all tire inflation systems are legislated to use real time data from each wheel. Therefore inflation is no longer inferred as a function of tire rotational speed, but as digital data broadcast by a pressure transducer located inside each wheel.
No because although the ABS computer still gets rotational speed of each wheel it gets it from a tone ring (a ring which generates an off/on signal X times as each wheel rotates. This signal is hardwired to the ABS computer.
Both because although the car knows the signals from each sensor it no longer has to mix the two for ABS and TPS monitoring. The two signals are discrete and handled separately.
(As an aside the ABS signal is the one used by the computer for stability control- as well as anti-lock braking functions)
(Aside #2. The TPS monitor inside each wheel is battery powered. These batteries are going to fail in roughly 7 years. The dashboard warning light -ABS- will illuminate when this happens. Be prepared to spend some money. Lots of money.)

e=mc2

Very good Slant, but can you tell us why?

Originally Posted by slant83

e=mc2

Since when?

E=mc^2 as far as I am concerned. Not that it matters in the greater scheme of things.

On a side note, DSX, great answer. How much can a dang battery inside valve stem cost?

I think when I priced tires on discounttire.com they said the replace the TPMS valve stems and they hardly charged but maybe $10 for those.

Not sure what to make of all that, so...

Originally Posted by cwinter

Since when?

E=mc^2 as far as I am concerned. Not that it matters in the greater scheme of things.

On a side note, DSX, great answer. How much can a dang battery inside valve stem cost?

I think when I priced tires on discounttire.com they said the replace the TPMS valve stems and they hardly charged but maybe $10 for those.

Not sure what to make of all that, so...

Hi CW. Some TPS monitors have replaceable valve stems, these are called insert types. You keep the same electronics and use a new valve stem (and related small parts).
The batteries themselves will probably go for around $5-10 each. The labor will be a killer. We'll have to remove each wheel from the car and break one beed to gain access to the monitor. The old monitor must be removed and disassembled to swap batteries. When it is reinstalled a new seal kit will be required. After reinflation the tire should be rebalanced-it doesn't have to be but it would be a shame not to check it at least. Then the wheel has to be reinstalled on the car.
My guess is that fewer than 10% of all machines in use today can quickly and safely handle RFTs so your choices of who will do the work will be limited. (Most BMW dealers obviously are equipped to do the work.)
My estimate to replace four batteries by an independent; $160-180. By a BMW dealer-more.

Originally Posted by DSXMachina

Hi CW. Some TPS monitors have replaceable valve stems, these are called insert types. You keep the same electronics and use a new valve stem (and related small parts).
The batteries themselves will probably go for around $5-10 each. The labor will be a killer. We'll have to remove each wheel from the car and break one beed to gain access to the monitor. The old monitor must be removed and disassembled to swap batteries. When it is reinstalled a new seal kit will be required. After reinflation the tire should be rebalanced-it doesn't have to be but it would be a shame not to check it at least. Then the wheel has to be reinstalled on the car.
My guess is that fewer than 10% of all machines in use today can quickly and safely handle RFTs so your choices of who will do the work will be limited. (Most BMW dealers obviously are equipped to do the work.)
My estimate to replace four batteries by an independent; $160-180. By a BMW dealer-more.

the BMW tpms sensors are sealed-- there doesnt seem to be a way to open them up to replace the battery. the top is a solid plastic shell, the bottom looks like a silicone potting material.

OE Beru sensors without the stems are 40 each. OEM sensors (Beru) cost about 70 each.

Originally Posted by Orient330iNYC

the BMW tpms sensors are sealed-- there doesnt seem to be a way to open them up to replace the battery. the top is a solid plastic shell, the bottom looks like a silicone potting material.

OE Beru sensors without the stems are 40 each. OEM sensors (Beru) cost about 70 each.

Thanks for the info Orient. I didn't know BMW used Beru's, there are 7 different types and I haven't messed with a Beru yet. I did have to change a Toyota sensor recently. It took a battery but the problem was in the circuitry.
If the sensor will have to be changed this job is going to be even more expensive than I figured. I can imagine a lot of cars being driven with the little dashboard tire profile and the exclamation point lit up forever.

Originally Posted by DSXMachina

I can imagine a lot of cars being driven with the little dashboard tire profile and the exclamation point lit up forever.

+1
I've only had 3 days where I DIDN'T have at least the little exclamation point lit up (for different reasons).

DSX, when i bought a set of winter tires/wheels from TireRack the TPMS sensors were only $196 for a set. That doesn't seem like "lots of money" at the BMW level of ownership... Are you talking about something else?

Do the passive sensors have the same battery issues? I have an early build 07 so i have just the FTM I believe (rubber valve stems).

Originally Posted by 1CEBITN

Do the passive sensors have the same battery issues? I have an early build 07 so i have just the FTM I believe (rubber valve stems).

there are no sensors and therefore no batteries in FTM

Thanks, Orient, that is probably the only advantage to FTM over TPMS but it is one less thing to worry about!

Originally Posted by Shocktopus

DSX, when i bought a set of winter tires/wheels from TireRack the TPMS sensors were only $196 for a set. That doesn't seem like "lots of money" at the BMW level of ownership... Are you talking about something else?

TireRack's TPMS sensor prices are unbeatable. Their prices are close to what I pay wholesale, they are not losing money, and they are making it on the tire sales. My margin would require that I sell these for at least $60 each. If I sold $800. worth of tires at the same time I might drop the sensor price a bit.
So take 4X60=240 and add 28 ea. for labor and balancing and now you're up to $352. That is a lot of money to many posters on this board. In the grand scheme of BMW ownership it isn't, but to turn off a warning light (which can be obsoleted with a tire pressure gauge) it is.

Originally Posted by Shocktopus

DSX, when i bought a set of winter tires/wheels from TireRack the TPMS sensors were only $196 for a set. That doesn't seem like "lots of money" at the BMW level of ownership... Are you talking about something else?

$196 is almost the cost of parts for front rotors/pads from the dealership. You must be talking about the set of bmw owners that dont know the "righty tighty, lefty loosy" rule.

$196 for a set of "sensors" really does suck, considering my 06 330i doesnt need them.

You can thank our government for the new, pricey direct TPMS systems. It's because Americans can't be bothered to regularly check their tire pressures.

BMWs in most other countries including Canada still use the FTM method.

Originally Posted by DSXMachina

Both? Yes and no, and not maybe. (How's that for narrowing it down?)
Yes because all tire inflation systems are legislated to use real time data from each wheel. Therefore inflation is no longer inferred as a function of tire rotational speed, but as digital data broadcast by a pressure transducer located inside each wheel.
No because although the ABS computer still gets rotational speed of each wheel it gets it from a tone ring (a ring which generates an off/on signal X times as each wheel rotates. This signal is hardwired to the ABS computer.
Both because although the car knows the signals from each sensor it no longer has to mix the two for ABS and TPS monitoring. The two signals are discrete and handled separately.
(As an aside the ABS signal is the one used by the computer for stability control- as well as anti-lock braking functions)
(Aside #2. The TPS monitor inside each wheel is battery powered. These batteries are going to fail in roughly 7 years. The dashboard warning light -ABS- will illuminate when this happens. Be prepared to spend some money. Lots of money.)

Well... I'd say indications are that both systems exist in my car. Here are two images taken from the manual. They are clearly describing both systems. I KNOW the TPMS is in place. I strongly suspect that the FTM is in place. (My only hesitation has to do with the asterisk indicating it's an optional feature. My car is loaded, so I'd be surprised if I didn't have it.)

Originally Posted by ProfessorCook

Well... I'd say indications are that both systems exist in my car. Here are two images taken from the manual. They are clearly describing both systems. I KNOW the TPMS is in place. I strongly suspect that the FTM is in place. (My only hesitation has to do with the asterisk indicating it's an optional feature. My car is loaded, so I'd be surprised if I didn't have it.)

Hmmm. I can tell you that my '07 owner's manual has some obsolete information in it, maybe your 328 manual is similar.
Comparing tire rotational speed (for purposes of determining proper tire inflation) in a car with TPMS is not only redundant, it is unneccessary. That would be like having sealed beam headlamps alongside xenon, like having a carburetor along with fuel injection, like manual seat controls with power adjustable seats. I can't see the need.
My guess is that either the copy editor missed it, or it's referring to the same system.
Did you say you purposely underinflated one tire and drove that way? Did the TPMS light come on or a different warning?

I underinflated by about 5 psi and drove it less than 50 feet to see. 'Sure enough, I got the warning light. Assuredly this is from the TPMS.

I understand what you're saying about a redundant system, but perhaps it's there anyway. It would take almost no extra effort or expense to incorporate the FTM.

My guess is it is in the owner's manual b/c TPMS is on some cars and FTM is on others so they give you info on both and it is up to you to know what you have. You don't have both. My 07 doesn't have TPMS for example, I only have FTM. Other countries don't require it like the US does and it is cheaper to build a car without it...

Originally Posted by bluskye

$196 is almost the cost of parts for front rotors/pads from the dealership. You must be talking about the set of bmw owners that dont know the "righty tighty, lefty loosy" rule.

$196 for a set of "sensors" really does suck, considering my 06 330i doesnt need them.

I'm not sure what your point was here. But I ordered a set of wheels/tires and the TPMS sensors were pre-installed. That way I have two sets of wheels both with TPMS. It's handy to have, especially with RFTs. It's let me know of a leak before I could tell already, and I've only got 6000 miles on it.

I'm sure I'll come off sounding like a dick and I don't mean to, but if $200 every seven years (or extra set of wheels) even mattered to me, I'm driving the wrong car and should have gotten something cheaper. I paid more than double that for the frivolous ability to not take my key out of my pocket to unlock and start the car. Christ I spend more than that on booze in a month.