My 2009 X has TPMS in all 5 tires including the spare. I took them out and put them in my MT 35x13.50's.

 

Why should they have done that?

 

This is how it all went down: I brought the Jeep to Clayton offroad yesterday a.m. with the new wheels and tires unmounted. Clayton is putting the lift on and mounting the new wheels/tires. I asked them to swap out the TPMS. As we were walking around the jeep discussing what was to be done we noticed that the spare stem was a plain old rubber stem ( from factory, I assume). At any rate, now my spare will be without a TPMS stem until I get one. No big deal really. I still have the stock spare mounted on the stock wheel. I will just take that to the dealership, show them what I found and ask them what's up. I would hope that they would be happy to hand me a TPMS stem for free and i will deal with getting it into the aftermarket wheel. It really would be a non issue but I was hoping to do 5 wheel rotations.

 

yeah, mine came on all five tires. In fact (and I don't know if this is true) the dealer told me that the computer is monitoring all 5 stems. I asked what that ment and he said that if I were to take the spare off and drive away, it would chime that something was wrong (low pressure, high pressure, missing) So if this is true and your not getting any warnings, then I wonder if your remaining 4 tires with the TPMS is even being monitored.

 

I think what the dealer told you is hogwash. I have aired the four tires down and had the light come on, as soon as I air them up, it goes out. I think the computer only needs to see 4 because that is all you will ever have on the road. Once you change out a wheel and put the spare on, it still only sees 4... that's my take anyway. So i need the other one in order to rotate all 5 wheels.

 

all right, I'm confused.

How DOES the tpms work?

I know it is a battery powered RF signal. Is it based on proximity?

And what about the spare? Does the system automatically look for 5 signals or does it just measure the signals it actually receives? I mean, if you only have 4 TPMs sending signals, does the Jeep "care" that the 5th is missing?

Or does the system only care about the signals it actually receives? I remember a poster saying his system was picking up signals from wheels he had sitting in the garage along side his Jeep.

Anyone have battery issues yet? IS their an expected lifespan? Will the system give a "low-battery" warning?

Thanks, I suddenly felt ignorant ......

 

Because you need the sensor out of the spare to put in you new wheel.

Im not sure for Jeep, but I am a tech for BMW and our systems monitor all 5 wheels, spare included so that if your spare ever gets low on air for whatever reason you will know so you arent stranded on the side of the road with a blowout and a flat spare!!

 

Yeah. I don't why I asked that question.
I read the FSM about how the system works.
It looks to me like the spare goes into Park mode and updates its pressure every 13 hours. The wording is very sketchy at best, but that's what I got out of it.

 

I know mine is checking all 5 wheels. Less than a month after getting my Jeep I got the TPMS warning while driving home from work. I had checked the air pressure in the 4 tires touching the ground when I brought it home from the dealer, so i figured I had a puncture or slow leak. I whipped into the first gas station I came to and checked out the 4 tires on the ground.......everything seemed fine

I started up the Jeep......no more warning. 10 miiles down the road the TPMS went off again. Damn it, now I think my new Jeep has a problem. About half way home I thought about the spare. Sure enough.......when I got home I checked the spare and it was right on the hairy edge. I shot a couple of PSI into it and haven't seen the warning again in the past 6k miles

 

This was my experience too. But to throw a wrench into things, I have since broken a sensor off and replaced it with a regular valve stem; this is the spare tire now. So I only have 4 sensors and I do not get any warnings. I have assumed that as long as the system is receivng at least 4 signals, it does not care about the 5th, but will report it if it is there.