It's a MEMS (Micro Electro Mechanical System) pressure sensor integrated onto a silicon die with a bunch of other components (CPU, transmitter, accelerometer, temperature sensor possibly). I don't know who manufacturers the silicon used in the Jeep's sensors, but here's a brief backgrounder on MEMS technology from Freescale Semiconductor:

MEMS-Based Sensor Technology

Here's a photo I snagged off the FCC web site then annotated showing the pressure sensor:



By the way, MEMS technology is what is used to make the sensors for the airbag and traction control systems as well as the sensors for the wiimote.

-Glen

 

Each TPMS sensor has a unique serial number and your ECU locks itself to the four / five serial numbers of the sensors in your wheels after a reflash (hopefully). Your ECU will then ignore transmissions from other vehicles' TPMS sensors. Does anyone know any of the details on training the ECU to recognize a given set of sensors after a swap of all four sensors?

Here's my evil idea:

1) Build a small RF receiver and transmitter.
2) Receive the "pressure good" message from the car next to you at the light.
3) Change the message to read "pressure bad."
4) Rebroadcast it over and over again.
5) Repeat for every car in the vicinity except yours.
6) Laugh as everybody pulls over to look at their tires.

It's also possible to embed antennas in the roadway and track vehicles by the transmissions from the TPMS sensors.

It's sh*t like this that becomes possible when security isn't designed into a system at the start.

-Glen

 

[QUOTE=tackindy;267203]I put Cragar Soft 8s on and I had heard the stock sensors would not fit so I did not switch them over. Here is what happens.

QUOTE]

I also have an 08 with Craggar soft 8's. The sensors fit in my wheels no problem. Just have to remember to change out the valve stem core for a new one when you take them out to air down.

 

So There is also a monitor in the spare that is actively monitored so if your spare goes down you'll get the light

 

Okay, I have an 07 Unlimited Rubicon. Bought it used with 18" Sahara Wheels and Tires already on it. So, obviously the stock tires are not on it. I have never had the TPMS light come on and i am about to swap to 17" wheels and 285/70/17's.

I wanted to see what it would do when aired down just to see how annoying the light or ding would be (and if i could / could not live with it). I first aired down one rear tire to about 22psi thinking that it would activate the light...nothing. I drove around my neighborhood and down the highway up to about 60mph. No light. No ding

I aired down to about 15psi and tried again, same driving and still NO TPMS light or ding.

My question is, are my TPMS's working? Shouldn't the system go into alarm pretty soon when a tire goes down?

I aired down in my driveway, then cranked up and drove. SHould i try driving, parking and leaving it running while airing down, then drive again.

My main question is if i need to get the sensors swapped over to the new wheels and tires? Or if they are not functioning? Maybe the previous owner disabled it somehow? Anyone with any input on this would be appreciated. Thanks.

 

I believe the 07's did not have the monitoring system...08 and newer

 

Thanks, I was beginning to go crazy trying to figure out why i couldn't get the light to come on. This would make my wheel and tire swap much easier since they won't have to break down all the old ones and remove and relocate tpms sensors.

I may have them break down one of the old ones just to see if they have the sensors in there (since they are not the wheels that came on the Jeep). I am not sure what year model the wheels came from. Then if i sell them, i can at least accurately advertise them. I have just always assumed that it had tpms.