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2010 FORESTER
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Discussion Starter #1
I have a 2010 Forester...just took delivery less than 2 wks ago. Today I'm driving home from an appt (about 50 min each way) and within a couple miles of home the Tire Pressure Warning light comes on and stays on. I did continue on home and checked pressure immediately. All 4 tires were at 50 lbs. (supposed to be 30/29 cold) It is sunny and warm here today in Massachusetts - 77 degrees.

Is that too much for them to "heat up" in driving, and is that why the warning system kicked in? I tried calling the service dept of my dealership but they're closed. I do plan to check first thing in the morning when the tires are cold and of course if they are overinflated, I will release some pressure, but I don't see how that could be...the entire car was gone over when I took delivery and everything was perfect.

I'm guessing at this point that the tires themselves are ok...if I had picked up a nail or something I would have expected one tire to be at a different pressure than the others. Of course I may go out in the morning when they are cold and find them all flat:icon_mad:

Any thoughts or experiences with the system, and what might be going on? I have a feeling I'll be missing work Monday to take the car in to the shop - not something I expected from a 2 week old Subaru.
 

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2010 Forester
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My dealer likes to adjust the tires to 45 PSI which makes the car drive poorly. It is a lot happier at the recommended pressures. Many suspect the reason some dealers put in so much air is to keep the TPMS from alerting too often.
 

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2009 2.5X Limited 4EAT
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All four tires are at 50PSI? Is that safe/recommended on a 2010? I mean, recommended psi on my 09 is 32 front and 33 back. Dealer puts them at around 35/36. Fine.

I could be missing something. What again is 50lbs.?
 

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2010 FORESTER
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Discussion Starter #4
Thomas, thank you for your reply. I wonder, if your dealer sets the pressure high to prevent the system from being triggered too often - does that mean there is no "upper" limit that would set it off? I was just wondering if that is what happened to me....that it got to 50# and something got triggered.

It will be interesting to see what the "cold" pressure is....I'm planning on checking in the morning because I've heard that you need to wait at least 3 hrs or more to let the tires cool....
 

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2010 FORESTER
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Discussion Starter #5
Bellatech, thanks for answering....
the tire pressure per my gauge was 50# when I got home. specs call for 30# in the front and 29# in the rear....but I understand that when the tires heat up, the pressure goes up. was wondering if the combination of warm day and long car ride pushed it up to the point where the system was triggered - if the system is designed to trigger for too much pressure as well as too little?

perhaps I will be that much wiser when I check them cold, in the morning. if I find that the dealer set them at like 45, I will let some air out to bring them closer to specs. I don't mind a cold pressure of a couple pounds higher than specs....but I don't want to endanger the tire, the car or myself by having it too high.
 

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2010 Forester(sold 11/12) Manual
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Fairly recently, I was in a rental car (not a Subaru) that had both the TPMS light and also a read-out that showed tire pressures. I noted that, as I left the rental car company, the tire pressures were pretty high. After I had driven a while and parked for a few minutes, the TPMS light came on. The light seemed to be triggered by the tire that was over 60 psi. I adjusted the tire pressures to something more reasonable and there was no more TPMS light.

My point is that, at least in that car (a GM), the TPMS was triggered by too much as well as too little pressure.
 

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2009 2.5X Limited 4EAT
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Yeah, tires get warm, but seriously, not to 50psi on a nice Mass day. I mean, maybe if you were up around 40 and were rolling around in the desert, from morning to afternoon, I could see a 10psi difference, but in your neck of the woods, you're probably fluctuating 3-5psi all day.

I mean if it's 40F in the morning and then 77F in the afternoon, you'd probably see a fluctuation of about 7psi max. So, in short, I think 50psi is a little high, not to mention and uncomfortable ride. I would deflate those bad boys to a just a bit above what is recommended (cold). And go from there. 50psi is a little scary to me.

Generally, from what I've heard. the TPMS only goes off when your tires are severely deflated, not over-overinflated, but that may be different on the MY10. I would still deflate and see what happens.

Check these out--
http://www.subaruforester.org/vbulletin/f72/225-55-17-tire-pressure-48371/

The link wasnt working before--click on "Air Pressure. Temperature Fluctuations"
 

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2010 FORESTER
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Discussion Starter #8
Bellatech, I tried the second link but it didn't work.

We just checked the pressure again (3 hrs sitting in the shade) and they were about 48#. (outside temp is cooling into the 60s) I'm going to let it sit all night so they're good and cold and if they are still up there, I'm going to let some air out before we take off for church.

If the dealer truly did set them too high, I wonder why it is only today that the warning went off; on the weekdays I have a 45 min highway drive each way to work and back, and its only today, with the warm temps, that the light went on.

I truly hope that is the answer and want to thank everyone for their input, as it made me feel a little bit better than just worrying that there is something "wrong." If its just overinflated tires, that is "wrong" but easy to fix, at least:icon_rolleyes:
 

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2010 FXT
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the tpms sensor they put in these cars are going to respond to any type of extreme weather condition regardless of it being cold or hot. for every degree below freezing you loose 2 psi, so since it's early spring and the temp bounces from freezing to mild in the spring that stupid light is going to come on. it does it it my wife's 2010 xt and she gets all worried about it. tires heat up and cool down, it happens. i work for the sponsor of this this little section and i deal with it all the time. your best bet is keep track of your air pressure atleast once a month. hope that helps.
 

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Discussion Starter #10
Thank you, My10FXT...it does help. All the info has made me worry less that I have a bad tire(s) and more that it is either maybe overinflated tires (will be checking them this morning, now that the car has sat overnight) or some system sensitivity.

The light flashes at first, then stays on. My owner's manual says that behavior is indicative of a system malfunction as opposed to a tire malfunction, and to bring it to the dealer if it does not resolve after I check/adjust the pressure. If it has to go to the dealer every time the light goes on, its gonna be a huge nuisance...its not like they are right around the corner...not to mention missing work time.

Happy Easter to All!
 

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2015 Highlander AWD XLE 6AT
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...for every degree below freezing you loose 2 psi,...
:huh: Dropping 2 psi for every degree below freezing just doesn't compute. For example, it means that if an ambient environment changed from 32 F to 17 F -- a 15 degree drop -- a tire initially inflated at 30 psi would be flat (0 psi).

Tire pressure does indeed change along with variations in ambient temperature, but not to this extreme. Figure on an ~1 psi change (up/down) for every ~10 degree F change in ambient temp (up/down).

See: Tire Tech Information - Air Pressure, Temperature Fluctuations

My '09 Forester's owner manual contains a related discussion on pages 11-31 and -32.

HTH,
Jim / crewzer
 

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I once design some equipment for TPMS activation.
The sensor I have to deal with have 4 modes:
1. Shipping mode. Sensor basically only respond to a wake up code from activation tool and only to change it to other mode. Sensor does not send any data out.
2. Diagnostic mode. Basically this is the OEM manufacturer used to program the sensor to the receiver in the car.
3. Driving mode. Sensor send signal to the receiver in the car once per minute. Activation tool does not work anymore to prevent registering other car signal.
4. Parking mode. Sensor goes to sleep to safe battery when the car stop moving.

The problem with running the tire pressure to above 50 psi is it cause the sensor to goes to diagnostic mode where it would only send signal out if activated by activation tool. The receiver loss signal and thus sense something is wrong and turn the warning light. Lower the pressure below threshold and it would turn back to driving mode automatically after a certain time. So to sum it up most low end TPMS does not have high pressure threshold but it could cause it to reset to diagnostic mode.

This is mostly valid for low end TPMS system that does not show pressure reading on the dash. The high end TPMS are different and most of the time you do not even need activation tool.
 

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2009 2.5X Limited 4EAT
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See: Tire Tech Information - Air Pressure, Temperature Fluctuations

My '09 Forester's owner manual contains a related discussion on pages 11-31 and -32.

HTH,
Jim / crewzer
This is the link I was trying to pass along earlier. Mucho help.

Here is a thread with massive amounts of info on Subarus TPMS.
http://www.subaruforester.org/vbulletin/f72/tpms-sensor-replacement-33939/

Our sensors have a low pressure trip point and a high pressure trip point. Low 26psi, high 50psi.
This confirms my suspicions of why you're getting the TPMS to activate at 50psi.

Done and done. :icon_cool:
 

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Discussion Starter #15
Thank you again, everyone.
I checked my tires first thing this morning and all were at 48#. Guess that explains why they managed to reach 50# after driving. Wonder why it took the system so long to give me a warning...I've put about 800 miles on the car these last two weeks and yesterday was my first indication of trouble.

I'm going to call the Service dept tomorrow and ask them to check it, but meantime I reduced the pressure to 40# cold all around. I know the specs say 30 in front and 29 in rear but somehow I couldn't bring myself to let almost half the air in each tire out! The system seems happy...I drove it a couple miles and the light went out.

I have to admit that I was much happier with my '01 Outback that didn't have any idiot lights and depended on me to take care of it. Somehow we managed 168,000+ trouble free miles without a TPMS:bacon:
 

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hey i kinda had the same problem the past two days. i am on the coastline of north carolina and the past two days i have gone to the beach. i noticed about a 10 degree temp drop in about 3 to 5 minutes and my tire pressure light would start blinking, then just stay on. i think it was due to the sudden change of temp i was driving through. im not sure if that could be the same thing with yours but watch ur therometer and if you see a big drop or rise in temp and then your tire pressure light goes on that could be it. i am no expert that is just my findings. i hope i could help
 

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<snip>

I have to admit that I was much happier with my '01 Outback that didn't have any idiot lights and depended on me to take care of it. Somehow we managed 168,000+ trouble free miles without a TPMS:bacon:
I suspect that most (if not ALL) users of this forum are going to know that they have a low tire and do something about it. Yet, I'll often see someone (not in a Forester of course) "cruising" down the highway with 15 lbs or so in one tire. I see TPMS as an attempt to protect them (and us) from the consequences of that behavior. And we all get to pay for that innovation.
 

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I'm going to call the Service dept tomorrow and ask them to check it, but meantime I reduced the pressure to 40# cold all around. I know the specs say 30 in front and 29 in rear but somehow I couldn't bring myself to let almost half the air in each tire out! The system seems happy...I drove it a couple miles and the light went out.
did you get a chance to call the dealer? Our '10 Forester is 3 weeks old, and my wife was driving on 128 (yeah we're from MA also) and the light went off. I just got back inside from checking and the tires were 45-48 psi, that's after cooling down for about 2 hours. Did you deflate to the 30s? I wonder if the dealers are putting so much air in so the MPG is really maximized and they get fewer complaints.

If the TPMS trips at 50, I'd feel ok about putting 40 lbs max in the tires, but not 90% of the error threshold.
 

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i recently got new All Terrains from Discount. the tpms light was always flashing arbitrarily or staying on all the time. finally took them back to Discount to ask what was going on. they in turn double checked the code (or something like that) that is particular to each vehicle make/model. they didn't have a code for the newer Foresters so grabbed one from an Outback that was a few years older. that seemed to do the job and i didn't have problems. then i rotated my tires and included my full size spare into the mix. once i did that the light started acting weird. back to Discount i went and this time they suggested that because not all the tires were at the same pressure, that's what was causing the warning light to flash again. once they made the pressure the same in all the tires, the lights been off ever since.
 
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