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Discussion Starter #1
After my 6000 mile inspection, the dealer rotated my tires and adjusted the air pressure. I now find myself in the situation, where I can either trust my two handheld pressure devices, or the internal car monitoring system. Hereby, I am not so worried about exact measurements, but to have pressures equally distributed. If I pump up all 4 tires the same way (35 psi on the dial, measured the same way), the car monitor shows 35, 34, 34, 33. Any suggestions for calibration (again, not to absolute psi, but to a relative measurement)? Mercedes does not show individual measurements and I am sure that it is for this reason. The system is not accurate enough and will drive drivers like me crazy. The solution could be (Jeep > hint!) to use the "reset" button to average the tire pressures left and right and show the developing differences in the future. But for now ... what choice do I have? Either have "nice and equal" readings with truly different PSI, or the opposite :(
 

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Makes ya wonder if your gas gauge is correct...:)

I don't think 1 pound difference in air pressure is anything I would be concerned about. Now if it was over 3 or 4 then I would do a little adjusting.

I notice that even when all pressures read the same when cold, that while driving the tire pressure does not increase/decrease evenly according to the TPM system...It's the same on our 2K3 GC Limited. But it is still a big improvement over no monitoring at all.
JC
 

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As far as them not increasing / decreasing at the same rate... makes perfect sense. Different tires will heat up differently depending if they are front or rear or on the inside or outside of the corner when turning, etc.
 

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Mine is pretty close to the guage. Also, they change by almost 10 degrees at times, depending on use.
I don't know of any way to "calibrate" them.
Good luck and let us know if you find a way.
 

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It says in the owners manual that this system is not designed for exact measurements and is only a quick reference on tire presure. Do your actual pressure readings with a manual pressure gauage at the stems....This system is only to monitor approx pressure and should only tell you when you have serious air loss....
Someones pretty anal if ya ask me..LOL:D
 

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Discussion Starter #6
... thank you for all your input ... I have ran a series of tests and found the error of my two gages (inexpensive stick and expensive dial) to be large enough to fit into the perceived error range of the Commander's display. Hence, after adjusting to the dial, I drove around the block (in both directions, as tire loads are different) and made fine adjustments to the air pressures until I got them all correct and within the tolerances of my gages. Having spend some time on this (I know some will shake their heads ... but I drive fully loaded long distances at high speeds), I think that I will fill to my gages display (a bit on the high side) and make the small fine adjustments by sticking my car key on the individual valve stem to let go where it is a bit high ... until the display is even.
 

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I'm loving the tire pressure monitoring system. My wife told me about a warning light on the dash and after checking found a nail in the front tire. Didn't realize we had this feature, thought this was only on the "Limited".
 

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The limited measures all 4 tires individually. The base model etc. will tell you when one is too low, but it will not specify which one or give pressure readings
 

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Yea, base model uses ABS wheel speed sensors vrs. in tire RF transmitter/dash receiver.
I know the G.Cherokees with in tire monitors used a calibration magnet to reset the system after a flat tire. Not with the Commander.
I was size testing different tires on ours at my work. After reinstalling the original tires I could not get the "Low Tire" warning display off. Giving up, on the drive home the system reset itself after about 10min.
 

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I was wondering if anyone knnows how to clear this, I replaced wheels and tires and now have the low pressure sensor flashing regulary
 

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I work at a Jeep dealership and have found the in dash readings to be pretty accurate but very sensitive. A slight bit above or below a line on your gauge will show up as a pressure difference on the dash, can be a bit annoying trying to get them all to read perfect.

If they are still flashing after tire and wheel replacement you need to inflate the tires to the correct pressure and drive it for a few miles. If you did away with the sensors when you changed the rims then it will not stop flashing. There may be a way to shut it off with a scanner, but we dont do wheels without the sensors so I have not looked into it.
 

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Out of curiosity, what pressure are users running??

Owner's manual recommends 35 psi, but max rating on sidewall=44psi (I think we all have Fortera-HLs).

I usually run close to max for longevity.
 

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Hello, 2c.

You can certainly run tire pressures at near max, but you will definately make the ride more rough. max pressure is really for max load
 

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Discussion Starter #14
I ran with the original pressures (34 cold stationary - 37 hot on highway) for about 10k miles. I have now switched (37 cold stationary - 40 hot on highway) and can notice a harder, less cushioned ride. I do not feel an improvement ride wise, but hope to get some better handling from them ... difficult to tell so far and I may try to find something in between in the future.
 

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Faustus said:
I ran with the original pressures (34 cold stationary - 37 hot on highway) for about 10k miles. I have now switched (37 cold stationary - 40 hot on highway) and can notice a harder, less cushioned ride. I do not feel an improvement ride wise, but hope to get some better handling from them ... difficult to tell so far and I may try to find something in between in the future.
Any noticable impact on gas mileage? Increasing inflation should improve MPG somewhat.
 

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If you are somewhat anal (like me) and would like to see the pressures all the same, remember this........

It takes a good half hour at highway speeds for tires to reach an equilibrium temperature. You can see this if you keep the system on display from the time you start. Pressures will go up and down and finally settle on some number (unless outside temperatures are changing rapidly).

My suggestion: try to get the pressures equal after driving at least a half hour on a highway. I just remember which tires need a little more air and which need a little less.

I finally have a perfectly balanced system......but only after driving for a while.

Yes, it does come close to what my manual pressure guage says.

However, when I start out after sitting for a while, the pressures are all different, but settle into balance after about 30 minutes of driving.

NOTE: This is only for the anal retentive that like to see the same numbers on the display.
 

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Too bad about the version of Fortera installed. The HL's are prone to premature tred wear. The newer Fortera SilentArmor uses kevlar and wears far better.
I'm running ours at a lower 32 front/30 rear cold.
Hot pressure increase is greater than 3 pounds. 37 cold will approace the tires max. pressure. If you want to run that high it would be safer to switch to extra load or 6 ply tires.
 

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Erik Latranyi said:
...NOTE: This is only for the anal retentive that like to see the same numbers on the display.
Besides the "visual", it's also important to have the pressures as close as possible for handling and steering purposes. I'm with you, the more exact the better. I find the TPM systems to be incredibly accurate and for maximum tire wear, mileage, ride quality etc. one should always stick with the pressures on the door label, unless as mentioned you have an unusually heavy load.
 
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