tpms....are they actually attached 2 the valve stems or are they in the valve stems?

 

it comes as a unit with the valve stem

i can't have them on my cragar soft 8's cause they won't fit i get 4 dings when i start the jeep and randomly get 1 single ding while driving.. think i have heard it 3 or 4 times in a total of 6 hours

 

They're completely integrated with the valve stems:

Warning: PDF file

https://fjallfoss.fcc.gov/prod/oet/f...ive_or_pdf=pdf

-Glen

 

so are they transferable to new set of rims? i am looking to get the pro comp series 8179
http://www.4wd.com/jeep-parts.aspx?c...d=168&plID=408

if so do i need to have the reprogrammed by the dealer? if i cant reuse them can the dealer get anotehr set.. didnt really want to go to the dealer to swap them as i am sure they will charge a lot...

 

Nope. Early TPMS were indirect reading systems and used the rotational speed of the wheels as measured by the ABS system to sense if one wheel was spinning faster or slower than the other three wheels. If this was the case, the TPMS would assume the odd ball tire was flat and alert the driver. The major drawback to these systems was that all four tires could be low on pressure and the typical idiot driver the legislation was designed to protect would be none the wiser. The major advantage was cost savings--no need to put sensors in each wheel--use the electronics that are already there for the ABS system.

The Jeep TPMS is a direct reading TPMS. The pressure of each wheel is directly measured using a micro electromechanical structure (MEMS) pressure sensor and radioed at 315MHz to the ECU using a sensor assembly that is integrated with the valve stem. In other words, the ECU knows the exact pressure of each tire. Just placing the sensors in a pressurized environment (a spare with five valve stems?) won't work because the sensors also have MEMS accelerometers that are used to wake the rest of the sensor up and report whether or not the wheel is actually spinning to the ECU too.

For more information, look for an earlier post of mine on another TPMS thread with links to both the FCC OET and USPTO documents I found on these things.

The long term solution is that the after market rim manufacturers will eventually incorporate space for the sensors in their rims and they will become an additional item on the invoice when you buy after market wheels with the tires already mounted and balanced.

The Jeep's system needs to let you set the alert pressure when in 4LO and monitor the status of the spare tire though.

-Glen

 

I'm willing to admit what I don't know and I don't know. Bueller? Bueller?

 

Well explain this then. I changed my wheels and tires and did not incorporate the stock valve stems (did not know at the time) fine for about 100 miles then light came on for awhile. Mysteriously the light went off and has not come back on ( cross my fingers) still have stock spare, so maybe its being checked or another theory is the stockers are still in my garage and the computer is still picking them up at start up.

 

Bingo! It's probably picking up the tires sitting in the garage. Even if the accelerometers don't pick up rotation, they still do wake up and transmit periodically--just less frequently than when they're rotating. I wonder how long the sensors can be missing before the TPMS in the ECU complains. What's the longest you've been away from home? Can you move the tires to the other side of the house for a day or two and see what happens?

I bet the ECU does pick up the tires even with the engine off--I aired my tires back up at the gas station and the computer knew the tires were back up to snuff without me doing anything other than turning the key and starting the Jeep. If the RKE is listening for the key fob with the Jeep off, it can listen for the tires with the Jeep off too.

-Glen

 

if the sensors are actually part of the valve stem then how come they wont fit in a new rim? sorry this is all greek to me

 

This is not a great picture... but you can see how it fits in the wheel.....some new rims don't allow the tire to fit with the sensor in there too.