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Old 12-15-2008, 09:02 AM   #1
bnaccs
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Default Tire pressure warning light

My 08 Outback Sport's low tire pressure warning came on for the first time today. The outside temp is -8. I assume this is the reason and that I don't have to add any air. I touched the tires and they all look and feel fine. Any thoughts are appreciated.
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Old 12-15-2008, 10:21 AM   #2
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If your low pressure light is on, your tires are probably low.

If your pressure is low, you need to add air. That's the point of the light.
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Old 12-15-2008, 10:25 AM   #3
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Quote:
Originally Posted by sniper1rfa View Post
If your low pressure light is on, your tires are probably low.

If your pressure is low, you need to add air. That's the point of the light.
second!! ^^^^ what he said
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Old 12-15-2008, 11:09 AM   #4
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well.....this is the first one of these I've seen

#1 and counting
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Old 12-15-2008, 12:19 PM   #5
Kean
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Quote:
Originally Posted by bnaccs View Post
My 08 Outback Sport's low tire pressure warning came on for the first time today. The outside temp is -8. I assume this is the reason and that I don't have to add any air. I touched the tires and they all look and feel fine. Any thoughts are appreciated.
....no offense but "touching" and "looking" is not an accurate way to tell whether your tires are inflated properly. Use a tire pressure gauge. Looks can be deceiving.
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Old 12-15-2008, 02:32 PM   #6
bnaccs
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I was worried if I try to fill the tires at -8 degrees that they will be overinflated when the temperature rises. I didn't know that the warning was a result of the cold weather, and I should wait until it is not so cold out to add air.
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Old 12-15-2008, 03:28 PM   #7
Kean
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....then I would adjust as needed. According to some sources, for every 10F degree change, you may expect roughly a 1 PSI change in pressure (lower temps = lower press and vice versa). If you adjust your pressure to meet the recommendations listed on the placard on the door jamb, I would think you should be fine. If the temperature swings wildly, I would simply check to make sure your pressure is still within reasonable levels.

The tires will have a maximum cold pressure stamped on the tire that you should not exceed. The recommended pressures are likely a few PSI below this so you have some wiggle room. ....on top of that, the max press is for "cold", so there is some leeway there as well. Also, if you are adjusting pressure in a garage that is warmer than the temperature outside, you need to take this into account and adjust as needed. .....the 10 degree/1 PSI general rule should help. I guess my point is that as long as you don't go overboard filling up the tires (and keep monitoring them as needed), I really don't think you should worry about overinflation issues.
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Old 12-15-2008, 06:50 PM   #8
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I went to Discount Tire and they added 2 pounds of air to each tire. Thy said it was just the cold. The light did not go off. Do I have to do something to reset it, or will it go off on it's own? I drove about 2 miles after they added the air and the light stayed on. Thanks again!
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Old 12-15-2008, 06:59 PM   #9
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....how much air was there or is in there now? IIRC the TPMS requires a minimum of 29 PSI otherwise the light will illuminate.
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Old 12-15-2008, 07:04 PM   #10
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fyi.... Have a look at the following article from Subaru Drive magazine:

http://www.drive.subaru.com/Spr05_WhatsInside.htm

Take special note of the table at the bottom of the page explaining adjustments you may need to make when consdiering temperature changes.
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Old 12-15-2008, 07:13 PM   #11
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Kean,

Thanks so much for the great article. There is 35 now in each tire.
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Old 12-15-2008, 07:16 PM   #12
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Quote:
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Kean,

Thanks so much for the great article. There is 35 now in each tire.
....no prob. I don't know why the light won't go off though. I would think it would reset itself after a few miles (with press above 29). ....maybe a failure in one of the transmitters (if that even would cause the light to trip)?
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Old 12-15-2008, 09:24 PM   #13
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drive faster than 40 miles an hour, if pressures are above 30 it will go out. If it doesnt, you have a bad sensor. Less than 36 k and its under warranty!!!
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Old 12-16-2008, 04:30 AM   #14
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if i remember correctly, if a sensor is bad or there is system fault, the TPMS light will flash. I've had the light come on and after tire servicing, it took about 10 minutes of driving for the light to extinguish.
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Old 12-18-2008, 02:36 PM   #15
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FWIW my light came on the other day when we got a nice cold spell. I figured that it was just the pressure loss due to the colder temps. I checked the tires and the pressure ranged from 29 to 31 which didn't seem too bad seing as the placard calls for 32. I raised them all to 34. The next time I drove it the light was still on. However after driving for a few miles the light turned off and has not been on since.
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Old 12-18-2008, 02:40 PM   #16
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the tpms requires rotation in order to become activated. if they do not detect rotation, they will not reset the sensor. i'm not sure on the timing of the amount of rotation vs. when a signal is sent back to the receiver, but iirc, the wheels have to be moving at least 10mph in order to activate them.
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Old 12-18-2008, 03:47 PM   #17
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....the sensors require that you be moving between 7-20 mph and will take readings every 30 seconds (transmitting every 60). ....it's all in the link I provided.
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Old 02-15-2009, 11:54 PM   #18
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re-bringing up the issue i guess...
i'm having a problem with the tpms - i bought a car, drove off the lot and 5 minutes later the light came on. turns out one tire had two nails and a razor blade in it! went and got a new tire, made sure the others were ok and the light is still on. maybe the sensor was damaged when the tech was putting on the new tire? i bought the extended warranty so hopefully it's covered.
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Old 02-16-2009, 05:45 PM   #19
Kean
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...if you bought it new and/or you're still within the 3/36 warranty, of course it should be covered. I would take it right back. .....assuming the tires are all properly inflated.
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