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Discussion Starter · #1 ·
Hey All,

A friend of mine got a flat today on his JK and was actually able to see the pressure drop of a pound or so every few minutes until he was able to pull over. He put on the spare and headed on down the road. After a few minutes it recognized the spare as being a new road tire and everything was dandy.

The system worked as intended, but when he was relaying this story to me it got us both wondering how the system knows what tire is in what location.

I searched on here and looked in the owners manual and everything I read leads me to believe that the tire sensors transmit to the security system receiver. There's even a note in the manual that says some types of window tinting can interfere with the signal, which would seem to imply that all the wheel transducers are broadcasting to a receiver inside the vehicle.

If that was the case, I don't see how it could possibly know what wheel is in which location, or how it could know to not include whichever one happens to be hanging off the tailgate. Logically, it seems like there should be a receiver in each wheel well somewhere, but if that's the case, then what's the deal with window tinting?

How does this thing work?
 

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When a JK has connectivity (individual tire pressure read out) there are three sensors on the chassis that monitor the four wheel sensors. That info. is then transmitted to the Wireless Control Module. There's no need for a fourth sensor since the computer uses the process of elimination to determine the fourth location. If there is no individual tire pressure read out, those sensors aren't needed.
 

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Discussion Starter · #3 ·
When a JK has connectivity (individual tire pressure read out) there are three sensors on the chassis that monitor the four wheel sensors. That info. is then transmitted to the Wireless Control Module. There's no need for a fourth sensor since the computer uses the process of elimination to determine the fourth location. If there is no individual tire pressure read out, those sensors aren't needed.
I read that as well (yay google) but I don't see how it can be true for the wrangler, which has 5 tires that all have transducers, not 4 (i.e. no process of elimination possible). In any case, where are the receivers located and why would window tint interfere with their operation?
 

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I read that as well (yay google) but I don't see how it can be true for the wrangler, which has 5 tires that all have transducers, not 4 (i.e. no process of elimination possible). In any case, where are the receivers located and why would window tint interfere with their operation?
The part of it that you're missing is that the spare tire isn't read until it's mounted as a road wheel and rotating. That's why the dash read out is only for the four road wheels. That's when the spare is picked up by the sensors. If there's connectivity, whatever position one of four that the spare is mounted, it's location is identified by the sensors. The process of elimination occurs because the four road wheels are only being monitored by the TPMS system/computer. That's also why when the tires are rotated the system knows the position. As far as window tint, I don't see how that would affect the sensors operation since the signal is going through glass, steel, plastic, etc., throughout the vehicle. The WCM is inside of the vehicle and it receives the signal. I guess Chrysler has info. which would indicate that heavy tint could cause interference. I haven't seen it but I'm not going to say that it's not possible.
Edit: Check this thread, my post #2, for the complete info. on each TPMS system and connectivity sensor location. http://www.wranglerforum.com/f274/2013-tpms-how-it-works-1570105.html
 

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I am sure my liberty measures the spare, but my jku doesnt.

Although i thought the liberty was cut price when i got it, the jk continues to surprise me!
 

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Discussion Starter · #6 ·
Okay, I'm definitely missing something. I get that the spare isn't read until it's mounted on an axle. The question is WHY?

If there are only 3 sensors, how does it know the difference between road tire #4 and the spare?

The only way that I can think of for this to work is that since the jeep has a full size road tire for a spare, there must be 4 wheel well sensors, not 3. I also don't think that it has anything to do with the tires rotating, otherwise the system wouldn't work while you're sitting still.

To further complicate this the owners manual describes the system as being comprised of;
-Receiver module
-5 tire pressure sensors (in the 5 wheels)
-various evic messages
-telltale light

There's no mention at all of wheel well sensors. but it goes on to say that a system fault can be caused by;
-Jamming due to electrical devices or driving next to facilities emitting the same RF as the TPM sensors
-some forms of aftermarket window tint
-lots of snow and ice around "wheels or wheel housings"
-snow chains.

So this returned me to my two original questions 1- How does it know which tire is in which position? 2-if there are individual receivers hard wired in the wheel wells per the google explanation(maybe 4, not 3), that answers question #1, but then why on earth would window tint matter?
 

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Okay, I'm definitely missing something. I get that the spare isn't read until it's mounted on an axle. The question is WHY?

If there are only 3 sensors, how does it know the difference between road tire #4 and the spare?

The only way that I can think of for this to work is that since the jeep has a full size road tire for a spare, there must be 4 wheel well sensors, not 3. I also don't think that it has anything to do with the tires rotating, otherwise the system wouldn't work while you're sitting still.

To further complicate this the owners manual describes the system as being comprised of;
-Receiver module
-5 tire pressure sensors (in the 5 wheels)
-various evic messages
-telltale light

There's no mention at all of wheel well sensors. but it goes on to say that a system fault can be caused by;
-Jamming due to electrical devices or driving next to facilities emitting the same RF as the TPM sensors
-some forms of aftermarket window tint
-lots of snow and ice around "wheels or wheel housings"
-snow chains.

So this returned me to my two original questions 1- How does it know which tire is in which position? 2-if there are individual receivers hard wired in the wheel wells per the google explanation(maybe 4, not 3), that answers question #1, but then why on earth would window tint matter?
If you read the info. in the link I provided, I added it later so I'm not sure you had the opportunity to review it, you'll see that there are only 3 sensors monitoring for individual tire pressures. There is no need for a 4th sensor. There is no 4th sensor because 5 wheels aren't monitored as was discussed. The spare has a sensor but it doesn't "activate" until it's mounted as a road wheel. It can take up to 15 miles/minutes for it to synch, or it can synch. relatively sooner than that. Each of the five wheel sensors have a specific code/signature that the system recognizes as far as what position that it's mounted. i.e.. RR,LF,LR,RF. That's why the correct wheels are identified when the tires are rotated. Any wheel can be used as a spare. The system will pick up it's location wherever it's mounted, just as if the tires are rotated randomly, for example, the computer knows where they are mounted for the dash read out. As far as window tint, I have no idea why that's included as a possible interference issue. I hope that this clears it up for you.
 

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Discussion Starter · #9 ·
I read all that....but the logic doesn't follow.

For example; If there are only 3 wheel well sensors, and you get a flat in the location without the sensor then replace that one with the spare, what causes the spare to "activate" when it's mounted on an axle? What causes the transducer in the flat tire to "deactivate" when it's put on the spare tire carrier?

It can't just be that it's rotating can it? If that were the case, the whole system would take 15 minutes to synch up every morning when you roll out of the garage.

edit: I just saw the post right above mine-Thanks to both of you for your input.
 

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Does the computer take the signals from the TPM and also use info from the wheel sensor? If a tire was going down, it's diameter would change and spin at a different RPM. Hence part of the reason for the time delay in readings.

When I air down all 4 and then re-air up, it usually takes a day or two to get where they all agree with the hand held gauge.
 

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Diagram

There are two tire pressure monitoring systems available, a base system and a premium system. The base system does not specify how many tires are low or where they are located. The premium system does so.

Both TPM systems consist of tire pressure monitoring sensors attached to each road wheel through the valve stem mounting hole and a TPM module. The TPM module (1) is fixed to a metal bracket (3) mounted onto the rear crossmember frame. The TPM module decodes the RF signals transmitted by each of the vehicle’s tire pressure sensors. The decoded information is used to determine if "warning" or "fault" conditions exist within the TPM system.

Upon detection of a warning or fault condition, the TPM module will send a request to the module that controls the indicator lamp and the text display via the vehicle bus system to illuminate or flash the indicator lamp. Also, upon detection of a warning or fault condition, the electronic display will send a request to sound the "chime".

The TPM module will store all warning and fault conditions, placard pressure values and low pressure threshold values (lamp ON and OFF) in memory that can be accessed through diagnostic communication. If new sensors are introduced to the vehicle, the data stored for the sensor being replaced will be deleted once the new sensor id has been learned.

The TPM module will store all wheel sensor ID’s and locations and faults in memory that can be accessed through diagnostic communication.

The TPM module automatically learns and stores the sensor IDs while driving “within 20 minutes continuously above 20 mph (32 km/h)” after a sensor has been replaced. The learning sequence will initiate when the vehicle has been stopped for more than 20 minutes.

The TPM Module (1) is a stand-alone receiver that is used to perform all TPM functionality in a Premium TPM System. The TPM is located on the top of the rear crossmember frame and is mounted with a bracket (3). The TPM uses information transmitted from each of the sensors as well as the difference in the strength of the signal received to determine the location of each of the sensors.

The TPM receives information from each of the sensors in the form of RF signals. The information contained in each of the transmissions provides all the information necessary for the TPM to determine the pressure in each tire as well as the position of the sensor. This auto-locating process only happens in the first 20 minutes of any drive cycle while traveling at speeds above 20 mph (32 km/h) (The auto-locating process will start again only if the vehicle has been shut off for approximately 20 minutes or longer). The TPM then transmits the required information directly to the CCN in order to update the lamp, chime and display as required.
 

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What if you swap wheels and tires from one JK to another? will it detect the new sensors? if their different year models?
Yep, there is a learn sequence every time you park it for more than 20 mins and start driving over 15 mph.

Each sensor’s (transmitter) broadcast is uniquely coded so that the module can monitor the state of each of the sensors on the four rotating road wheels. The module can automatically learn and store the sensor’s ID while driving “within 10 minutes continuously above 15 m.p.h. (24 Km/h)” after a sensor has been replaced. The vehicle must be stationary for more then 20 minutes in order to initiate the learning sequence.

Also, any 433 MHz TPMS should work with the factory receiver. 315 MHz sensors will not.
 

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This auto-locating process only happens in the first 20 minutes of any drive cycle while traveling at speeds above 20 mph (32 km/h)
This explains why mine take so long to reset accurately. It is only 7 minutes to work in stop and go traffic, so the jeep isn't moving long enough. Thanks for that information.
 

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Discussion Starter · #15 ·
Man I love this forum. 2016Rubicon, thanks for posting the data above. It was a silly question to begin with, but I was the kid who took stuff apart to see how it worked, and it was bugging me that I couldn't figure this out. Especially when I read that there were 3 wheel well sensors (which I've certainly never seen on my Jeep) responsible for 5 wheels.
 

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Diagram

There are two tire pressure monitoring systems available, a base system and a premium system. The base system does not specify how many tires are low or where they are located. The premium system does so.

Both TPM systems consist of tire pressure monitoring sensors attached to each road wheel through the valve stem mounting hole and a TPM module. The TPM module (1) is fixed to a metal bracket (3) mounted onto the rear crossmember frame. The TPM module decodes the RF signals transmitted by each of the vehicle’s tire pressure sensors. The decoded information is used to determine if "warning" or "fault" conditions exist within the TPM system.

Upon detection of a warning or fault condition, the TPM module will send a request to the module that controls the indicator lamp and the text display via the vehicle bus system to illuminate or flash the indicator lamp. Also, upon detection of a warning or fault condition, the electronic display will send a request to sound the "chime".

The TPM module will store all warning and fault conditions, placard pressure values and low pressure threshold values (lamp ON and OFF) in memory that can be accessed through diagnostic communication. If new sensors are introduced to the vehicle, the data stored for the sensor being replaced will be deleted once the new sensor id has been learned.

The TPM module will store all wheel sensor ID’s and locations and faults in memory that can be accessed through diagnostic communication.

The TPM module automatically learns and stores the sensor IDs while driving “within 20 minutes continuously above 20 mph (32 km/h)” after a sensor has been replaced. The learning sequence will initiate when the vehicle has been stopped for more than 20 minutes.

The TPM Module (1) is a stand-alone receiver that is used to perform all TPM functionality in a Premium TPM System. The TPM is located on the top of the rear crossmember frame and is mounted with a bracket (3). The TPM uses information transmitted from each of the sensors as well as the difference in the strength of the signal received to determine the location of each of the sensors.

The TPM receives information from each of the sensors in the form of RF signals. The information contained in each of the transmissions provides all the information necessary for the TPM to determine the pressure in each tire as well as the position of the sensor. This auto-locating process only happens in the first 20 minutes of any drive cycle while traveling at speeds above 20 mph (32 km/h) (The auto-locating process will start again only if the vehicle has been shut off for approximately 20 minutes or longer). The TPM then transmits the required information directly to the CCN in order to update the lamp, chime and display as required.
This is the best and only complete explanation of the TPMS system on this forum! :thumb:
 

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My 2014 JKU has the EVIC system. For the past few months the front passenger EVIC psi display has been blank, like its not reading the sensor. I just assumed its a faulty tpms sensor inside the wheel. The other three psi displays on the EVIC are fine.

So I rotated my tires yesterday and noticed the SAME front right corner is still not showing the psi, even though I've moved the tires around on my Jeep. That seems to indicate there's an issue with the receiver or tpm unit located on the back cross member. Is this correct? Has anyone experienced this yet?

Also, I've had AEVs with 285/70/17s for about two years now and the "Check TPMS" has been on ever since. The dealer tried, but wasn't able to figure out how to clear it (I tried airing up to 40 psi for a few days, etc. also). My Superchips FC was able to adjust the psi settings at first, but apparently Superchips took that function away during an update-synch at some point :rant:.
 

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My 2014 JKU has the EVIC system. For the past few months the front passenger EVIC psi display has been blank, like its not reading the sensor. I just assumed its a faulty tpms sensor inside the wheel. The other three psi displays on the EVIC are fine.

So I rotated my tires yesterday and noticed the SAME front right corner is still not showing the psi, even though I've moved the tires around on my Jeep. That seems to indicate there's an issue with the receiver or tpm unit located on the back cross member. Is this correct? Has anyone experienced this yet?
No, it's the TPMS sensor. I had that problem too on my first rotation. You need to replace the dead TPMS. As long as it's still one of the rotating wheels the system will have trouble updating the sensor location.

Also, I've had AEVs with 285/70/17s for about two years now and the "Check TPMS" has been on ever since. The dealer tried, but wasn't able to figure out how to clear it (I tried airing up to 40 psi for a few days, etc. also). My Superchips FC was able to adjust the psi settings at first, but apparently Superchips took that function away during an update-synch at some point :rant:.
AEV Procal can adjust PSI threshold so you're not getting the warning light.
 

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Thanks lumberjack.

Do you have EVIC? Seems odd that the EVIC display is showing the same three 'corners' (before AND after tire rotation) even though the suspected problem child was moved to a different axle, from the front passenger corner to the rear passenger corner.

I have AEV beadlocks , which means I can dismount the tire and install a new tpms sensor in my own garage and with hand tools, but its a PITA without the hot summer sun to soften-up the tires.
 

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Thanks lumberjack.

Do you have EVIC? Seems odd that the EVIC display is showing the same three 'corners' (before AND after tire rotation) even though the suspected problem child was moved to a different axle, from the front passenger corner to the rear passenger corner.

I have AEV beadlocks , which means I can dismount the tire and install a new tpms sensor in my own garage and with hand tools, but its a PITA without the hot summer sun to soften-up the tires.
I do have the EVIC. When I did my rotation it was my spare that was dead (went on to right rear), so my left front came off and was the new spare. The display showed left front with no reading now. I did extensive testing in this and got into an argument with my tire guy over it. I basically rotated my dead spare to every corner and my original front left to every corner (on my own time, not at the tire shop), at the end of it all I told the tire guy to put a new sensor in the suspected dead wheel and that the left front would magically come back and that's exactly what happened. All four corners updated. I then adjusted each tire to different pressures to identify location and they all matched up. And bc I proved him wrong they didn't charge me for swapping the sensor haha!

If you want to test this out before you buy a new sensor, if you have a spare with TPMS and put that on, so that all four wheels have working sensors, the EVIC will update. My situation was even more frustrating bc the tire guy insisted that my "dead spare" was still putting out a signal when he scanned it with his TPMS tool. Perhaps it was, but it wasn't getting to the computer. New sensor, all corners work, no annoying ding and light on start up!
 
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