The TPMS light has been on in my wife's 08 JKU for a while. I figured ignoring it was easy enough. I'm driving it this week due to mine being up on jack stands and I had to listen to that damn chime all the way in to work. A few months ago, a repair show told me it was likely that the spare tire was not equipped with a sensor at the last tire change and that was the cause. I've since read that a non-turning tire (spare) is not monitored and therefore would not be the cause. I've checked all pressures and they are within a half pound. I'm thinking maybe a bad sensor? Is there any way to determine which tire has the bad one? Or which wheel is producing the signal to set off the light/alarm?

 

I would say that sounds like a bad sensor.....same issue I'm currently dealing with, except on my '13 I can see it displaying the front passenger tire as dead.

 

You mean within a half pound of the pressure on the placard?

 

@Swampworks in our case, the sensor light went off on our new 2017 wrangler, pulled over and checked the 4 grounded tires. nothing to report. Yet checked the spare and it was below 30 psi. Adding some air to the spare corrected the sensor message. Therefor you have 2 options, either the Mech was right in saying there isn't a sensor in the spare or one of your grounded tires sensors is bad.

 

The OP is talking about an '08. The '08 doesn't monitor the spare. The reading I have done, and several experiments I have performed verify this.

His best option is to take it to a tire store and have them scan each sensor to see what it's transmitting, and check its battery condition..

 

@ronjenx This is assuming the Op has all of the original tires and sensors in them. But Let's assume for a moment that his wheels and tires are not the originals and all 5 tires have the sensors.. Would the 08 system catch the 5th wheel sort of speak?. Either way, if all 5 wheels have the sensors and one is going bad. then the system should catch this no matter what year the vehicle or how many sensors are involved.

 

I don't know if the WCM would pay attention to a fifth sensor should it be transmitting.
The JK sensors have a switch in them that closes when the tire spins. Otherwise, it goes to sleep until it's probed with a TPMS scanner, or it's place on an axle and driven.

 

@ronjenx 10/4

 

Neither does a 2017.....the TPMS for my spare is in the junk drawer at home.

 

TPMS are worthless, especially the ones on the early JKs where it doesn't tell you the pressure of each tire, and it doesn't tell you which tire is low. Just a worthless single light. I tried to troubleshoot mine with the shop that replaced my tires along with a couple of the sensors. They checked the sensors with their machine and stated they all checked out fine, told me I had to drive around for a couple days for them to re-calibrate and sync up. Never did get fixed. Could have been a dead/weak battery, or the new ones installed were the wrong frequency. Too much effort for me to find out, for no real value aside from turning off the damn ding and the light on the dash. I removed them, and got a Super Chips Flashcal and turned the chime/light off and life has been good. I do a visual inspection to see if my tire pressure is low, just like I did before they started adding these worthless tire pressure idiot lights. The newer ones are more useful like I mention, but work just as well as my daily visual inspection where I may even kick the tires if I want a more detailed inspection.

If you really want to hunt down that ghost without just throwing replacement parts at it, then you can get a OBD2 scanner like I got. The BlueDriver OBD2 scanner can read the wireless control module codes which will tell you which of the 4 sensors are acting up on a 2008.
https://www.amazon.com/BlueDriver-Bluetooth-Professional-iPhone-Android/dp/B00652G4TS/ref=sr_1_1_sspa?ie=UTF8&qid=1517375318&sr=8-1-spons&keywords=BlueDriver&psc=1
Here's the info it will provide you. Keep in mind I have all 4 sensors removed. Thus, the reason it shows 4 problem sensor codes. The 5th code BB2204 code is an error code logged due to me turning off the light with the Flashcal.