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Unread 08-14-2006, 08:19 AM   #1
Kev M
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Tire Pressure Monitoring System Question

Anyone have any information on how the Tire Pressure Monitoring System works on the new Compass?

Any system maintenance?

Are their remote monitors mounted in the wheels? Do they have to be recalibrated or does a control module need to be updated if they are rotated?

Just curious.

Kev

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Unread 08-14-2006, 11:06 AM   #2
XJ2Timer
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There are individual sensors inside each wheel. I would think that the system would just show a check tires light on the dash and it is up to the driver to check all of the tires to find the one that is low. It would be too complicated to have a system that displays which tire because as you point out, what about when you rotate the tires.
Personally, I think the tire pressure sensor thing is the wrong approach. It does nothing to change the habits of the drivers. The driver won't know a tire is low until it reaches the preset threshhold of the sensor. Drivers need to get back into the habit of checking things on their cars. I would have rather seen a law where car manufacturers have to provide a tire gauge with every new car and any place that sells fuel has to have a free air hose at the pumps.
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Unread 08-14-2006, 11:48 AM   #3
Kev M
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Quote:
Originally Posted by XJ2Timer
There are individual sensors inside each wheel. I would think that the system would just show a check tires light on the dash and it is up to the driver to check all of the tires to find the one that is low. It would be too complicated to have a system that displays which tire because as you point out, what about when you rotate the tires.
Personally, I think the tire pressure sensor thing is the wrong approach. It does nothing to change the habits of the drivers. The driver won't know a tire is low until it reaches the preset threshhold of the sensor. Drivers need to get back into the habit of checking things on their cars. I would have rather seen a law where car manufacturers have to provide a tire gauge with every new car and any place that sells fuel has to have a free air hose at the pumps.

Actually, the system on the Compass I demoed displayed PSI at each wheel position. (turns out 3 were at 36 psi and the rear left was at 35 psi ).

So I walked back in the shop to see if we had the 07 manuals yet (nope).

So I checked how the system works on a WJ, assuming the Compass is SIMILAR, but maybe not exactly the same.

Seems that on the WJ there are transmitters on/in each valve stem assembly which have unique identification codes. There is a computer (EVIC, I forget what that stands for) in the vehicle that receives the signals from the tire transmitters (including one for the spare). If you rotate the tires you have to put the system in learn mode and place a special tool (a magnet) over the valve stem of each tire, in a certain sequence, and the module will relearn the positions (i.e. reassign transmitter codes to new locations).

I'm pretty sure the Compass doesn't have a spare tire transmitter (or maybe it only does when optioned with the full-size spare).

Either way, if the system works in the same way IT SOUNDS like you can rotate your tires, but you'll need to get your hands on a sufficient sized magnet and the procedure for inititating the module relearn. I just glanced at the book and it sounded like it was accessed through the data display menu and not a scan tool, but again, can't say for sure and I can't say at all on a Compass. But time will tell.

I'll say I'm cautiously optimistic.

Kev
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Unread 08-14-2006, 12:18 PM   #4
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(Sorry, some of this is paraphrased…the Owners manual does get wordy)


Tire Pressure Monitoring System (TPMS).
This system uses wireless technology with wheel rim electronic sensors, mounted to each wheel as part of the valve stem, transmit tire pressure readings to the Receiver Module. The wheel sensors monitor tire pressure and status for four active road tires.

The TPMS consists of the following components:
Receiver Module
Wheel Sensors (attached to each wheel through the valve stem hole)
Wheel Sensor Trigger Modules (mounted in three of the four wheel wells)
Various Tire Pressure Monitoring System Messages, which display in the Electronic Vehicle Information Center (EVIC)
Yellow Tire Pressure Monitoring Telltale Light.

CAUTION!
The TPMS has been optimized for the original equipment tires and wheels. TPMS pressures and warnings have been established for the tire size equipped on your vehicle. Undesirable system operation or sensor damage may result when using replacement equipment that is not the same size, type, and/or style. Aftermarket wheels can cause sensor damage. Do not use tire sealant from a can, or balance beads if your vehicle is equipped with a TPMS, as damage to the sensors may result.

Tire Pressure Monitoring Low Pressure Warning
The Tire Pressure Monitoring Telltale Light is located in the instrument cluster. The light will illuminate and an audible chime will sound when one or more of the tires on your vehicle are significantly under inflated. The audible chime will sound once every ignition cycle for each condition that it detects.

When the appropriate conditions exist, the EVIC displays the following message:
(sorry, I can’t type the image but it says PSI, LOW TIRE, and has the read out for each tire)

Should this occur, you should stop as soon as possible, check the inflation of each tire on your vehicle, and inflate each tire to the pressure recommended by the vehicle manufacture. Once the proper tire pressure is set, the TPMS warning will reset automatically after driving the vehicle for at least 2 minutes at or above 15 mph.

Caution!
After inspecting or adjusting the tire pressure, always reinstall the valve stem cap. This will prevent moisture and dirt from entering the valve stem, which could damage the sensor.

NOTE:
The TPMS monitors the four active road tires on the vehicle, and can inform the driver of a low tire pressure condition, including low temperature effects.

(check pressure monthly)
The TPMS does not monitor the temporary spare
Should not be used as a tire pressure gauge.
Under inflation can cause the tire(s) to over heat.
Not intended to replace normal tire maintenance.

Check TPM System Message
The TPMS Telltale Light will flash on and off for 60 seconds and an audible chime will sound when a system fault is detected. The flash cycle will repeat every ten minutes, with out the chime until the fault condition no longer exists.

The EVIC will display the CHECK TPM SYSTEM message for 3 seconds. In addition, a graphic will be displayed indicating which of the TPM Sensor(s) is not being received.
If the ignition is cycled, this sequence will repeat, unless corrected.

Tire Rotation Recommendations.
No information concerning sensors.

Neither did I find anything in the EVIC “Personal Settings “ that would turn this off for off the road tires like they say were used out on the Oregon beach videos. Maybe Check TPM System Message covers that.

Last edited by Gramps; 08-14-2006 at 04:49 PM..
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Unread 08-14-2006, 07:54 PM   #5
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I apologise for replying when I didn't really know how the newer systems work. I remember when they first came out on the Corvette's with run flat tires and the sensor was strapped to the inside of the wheel.
I love how it says, do not use as a tire gauge and it is not intended to replace normal tire maintenance. Who comes up with this stuff? Human nature being what it is, the same idiots who never check their tires will be the same ones who are going to act like these sensors will solve all their problems and cure all their worries.
I am curious about how the sensor is part of the valve stem. Valve stems are routinely replaced when new tires are put on a vehicle. This is because the rubber in the valve stem gets old with age. How is this going to affect getting new tires? How many people, when they get new tires are just going to get rid of the sensors? Does anyone in the government who wrote this law know how many people get aftermarket wheels? And who when they are off roading and air down their tires for traction are going to want to keep listening to a chime? Isn't technology great?
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Unread 08-14-2006, 08:49 PM   #6
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No need to apologize, input makes people think. Computers are just number crunchers and only supply raw data, it takes a human to figure out what good it is. As far as computers and sensors replacing the brain, I think with some people it already has.
I wonder too about "how" they are actually "placed" in the valves. Do you have to go back to the dealer for valve stems or what?
The "low pressure" chime is only once and then when you switch off and back on, at least the way I read it.
I "think" that if you're running some special wheels and tires with out the sensors you will get the "check TPM system message" and that's only the initial chime and a flash cycle reminder every 10 minutes. I could live with that.
There weren't any details on the "Oregon Beach" run other that "equipped with special tires and wheels" or something to that affect, what ever that means.

"I love how it says, do not use as a tire gauge and it is not intended to replace normal tire maintenance." That was me paraphrasing the mundane soliloquy in the manual. Common since stuff for most of us.
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Unread 08-15-2006, 07:56 AM   #7
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To what "law" are you referring XJ?

Gramps, good info thanks.

I tend to run a set of winter tires on winter wheels. Sounds like this might limit that ability. Perhaps if I go this route I should negotiate a second set of wheels as part of my purchase price. Something to mount winter tires with their own monitors in the valve stems.

I'm anxious to get my hands on some service manuals and check out more about this system. Maybe if I get a chance today I'll wander out to the shop and read some more about the similar version on the WJ. Maybe that will answer the valve stem question.

Oh, we took a trip on the XJ this weekend. I don't drive it much in the summer. And before we left I figured I should check tire pressure.

DOH... "winter air" ... last time I filled em must have been 40 degrees colder out cause tire pressure wasn't at the 35 or so I run in the summer for highway/towing duty... it was 40+ psi. I aired em down a bit.

Managed to get 20 mpg average for the whole trip, keeping out of the throttle.

I couldn't help but think that I'd be getting about 10 mpg more in the same circumstances in a Compass.

Kev
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Unread 08-16-2006, 05:20 PM   #8
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I quizzed my dealer’s parts guy and one of the mechanics today. The sensors used on the Compass are similar to those used on other models but calibrated for Compass tire size etc. The low pressure warning goes off at 12 lbs. By changing rims and tires and eliminating the sensors you would get the single chime whenever you cycled the ignition switch and the dash light would flash once every 10 minutes after that. So someone answer for me please, is the sensor “built in” to the valve stem on other models or can you replace them separately? I forgot to ask them that, but they indicated that those would be dealer items.

Service manuals are not expected out until the end of Nov/beginning of Dec. Merry Christmas to me.

And Kev. How NICE it is to not have to keep my foot out of it to get the mileage. I've got a 4K trip down to AZ over Labor Day, we'll she how she does. And ya'll wecome for the info.
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Unread 08-16-2006, 08:00 PM   #9
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[QUOTE=Kev M]To what "law" are you referring XJ?
Kev[/QUOTE

Law or regulation or whatever it is where the tire monitors are mandatory now after the Ford Explorer Firestone tire thing.
If what gramps was told is true, recommended pressure is 35 and the low pressure warning goes off at 12. I know that the tire engineers know more than I do but I sure wouldn't want to be driving on pavement with pressure below 20. By the time it gets down to 12 psi a person can definitely tell visually that the tire is low. Sounds like the system is mainly meant to warn you when the tire is going flat while the vehicle is in motion. If the 12 psi is correct than this system would not have prevented any of the Explorer tire problems. Tread separation was happening because of heat buildup in the Firestone tires because Ford had been recommending running the tires at 26 psi for a softer more comfortable ride.
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Unread 08-17-2006, 03:46 AM   #10
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The Tread Act
Detroit news, 4/8/2005

http://www.detnews.com/2005/autosins...C03-143935.htm

According to this article, the 12lbs that I was told would be way below what was enacted but, I couldn't find the actual law. There are many after market manufactures of these monitoring devices that may have solutions to running different size tires and still keep the system accurate.

Additionally, if these monitors read psi and not volume, what difference does tire size make?

Last edited by Gramps; 08-17-2006 at 05:29 AM..
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Unread 08-17-2006, 05:56 AM   #11
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Interesting, I'm sorry to say that I've been out of the automotive loop enough that I had no idead the NHTSA had pursued such regulations.

The first yahoo search I made on it returned a district court of appeals overturning the law, or actually, sending it back to the NHTSA for clarification.

Perhaps that's why the systems are still optional on the Compass now and now mandatory.

But I guess they will be mandatory soon.

Overall, I like em. And if they are going to be mandatory, then there is a chance that places like TireRack will be able to install sensors on new Blizzak packages before shipping them.

I like the fact that this system can display tire pressure, so you don't have to wait for an alarm and dummy light. Just cycle through the menu once a week or anytime you're curious and get an instant readout of all 4 pressures.

Maybe I'll get off my *** today and go check the WJ manual again to see if I can find info on the sensor itself and what it involved in replacement.

If we get a Compass a set of winter tires is a must, so I'd want to make sure I can mount sensors and have a way to calibrate the control module when I swap/rotate.

Kev
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Unread 08-18-2006, 03:17 PM   #12
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Just some more general information from the Manual.

The example for Low Tire Pressure Display shows:

20 X 35
35 X 35

(So it looks like I may have been told 12 lbs. incorrectly.)

TIRE CHAINS
Due to limited clearance, tire chains are not recommended. (Looks like there MAY be enough room to me)

SNOW TIRES
Some areas of the country require the use of snow tires during winter. Standard tires are of the all season type and satisfy this requirement as indicated by the M-S designation on the side wall.
If you need snow tires, select tires the equivalent in size and type to the original equipment tires.
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Unread 08-20-2006, 11:09 AM   #13
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not sure if somebody stated this or not but our Commander has the tire pressure sensors and how my dad explained it is each wheel has a sensor and there is another sensor located on the body to correspond with each wheel position. So if you change the tires around it shows the correct tire pressure at the correct position.
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Unread 08-21-2006, 04:14 PM   #14
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Quote:
Originally Posted by JeepFreak91
not sure if somebody stated this or not but our Commander has the tire pressure sensors and how my dad explained it is each wheel has a sensor and there is another sensor located on the body to correspond with each wheel position. So if you change the tires around it shows the correct tire pressure at the correct position.

IF that's true, that system is different than the system used on the WJ through 05...
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Unread 08-21-2006, 05:53 PM   #15
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That's the same way that I read the Compass doing it except "Wheel Sensors attached to each wheel and Wheel Sensor Trigger Modules mounted in three of the four wheel wells. So rotation should be no problem.
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