Hunt it

If you take the tires off vehicle and leave in garage, the sensors will set off light when you pull into garage. In this case I'd say all 5 are inactive but computor still picks up sensors every time drive into garage.

JeepTechOlllllO

Hello
So I aired down my spare to 13psi and drove to work today. No TPM light came on. We all should check our spare ever so often because, it may go flat and we wouldn't know. And if that time comes and we need it :O it will not be a great spare :)
Unless you have an onboard compressor.

Jeepminded

Hey JeepTechO!!!!!!!O

First thanks for the clarification on the 5th wheel not having a sensor. Huh. Cost savings perhase?? You would think it should be (monitored) a flat spare when you need it will spoil the buffet line every time. :)

Do you know how these sensors report back to the computer? I have yet to figure that one out.
Thanks

Topbanana

Judging by the "important notes reguarding vehicles which come equiped with TPMS", that are listed under the rims, on TireRack's website, the sensors are emitting a radio signal similar to how a cordless phone communicates to its base station. They list 315mhz as the frequency a Jeep JK's sensors operate on, but that could just be the univeral frequency the aftermarket makers, (who provide the part to OEM) use.

JeepTechOlllllO

Hello Jeepminded
There is a TPM sensor on the spare wheel. it is just not transmitting a signal while the vehicle is driving.
On vehicles equipped with Tire Pressure Monitoring System, one tire pressure sensor (6) is mounted to each wheel in place of the traditional tire valve stem. Each sensor has an internal battery that lasts up to 10 years. The TPM system operates on a 315 MHz radio frequency(RF). An RF signals of 315Mhz is transmitted by each of the vehicle's active tire pressure sensors(the spare tires TPM sensor is in active) to the WIRELESS CONTROL MODULE (WCM) The WCM communicates with the module(cluster) that controls the "TPM telltale lamp", via the vehicle bus system. Upon detection of a warning or fault condition, the WCM will send a request to illuminate or flash the yellow TPM telltale. Also, upon detection of a warning or fault condition, the display module will send a request to sound the "chime". A chime will only be requested once per ignition cycle per warning or fault condition detected.

Jeepminded

Hi JeepTech0!!!!!!!0

Thanks very much for your detailed post on how the sensors work.

You are speakng my language (RF) it's my profession. Battery operated transmitters in your valves, cool! Make sense the spare has one, just not active as you say. Means I will now make sure I check it at lease once per month.

Jeepminded

Darn send button got in the way again....thanks also to Topbanana for answering my question.

Topbanana

Now if we just knew where they hide the WCM, we could disable the sucker and everybody's problems would go away. Back to checking tires the old fashion way, with a tire guage!

Jeepminded

Nothing beats a accurate tire guage.

Something else comes to mind....since each tire has its own RF transmitter, wouldn't it be kinda cool to have the data from each sensor conveted into real time air pressure per tire, and on a display showing all 4 corners....could even add the 5th tire out back. The dash display wouldn't do, it would have to be a seperate screen or something. Hmmm.

JeepTechOlllllO

Some Jeep models do this, Grand Cherokee is one of them. could be others.