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Below zero parked for several hours. Start up car and low tire pressure light is on all the way home. Next day go into garage and make all tires exactly what they should be according to the sticker on the door jamb and my digital pressure gauge. TPMS light stays on all the next day. What am I doing wrong shouldn't the light go off on its own?
 

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2017 3.6R Limited with Eye Sight
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Yes the light should go out...if you drive above 20 miles per hour.

The same thing happened to me. But when I added air, the light went out after a few minutes.
 

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2016 Outback Premium 2.5 CVT w/EyeSight+SRVD
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Next day go into garage and make all tires exactly what they should be according to the sticker on the door jamb ...
What was the temperature in your garage? Remember that tire pressure varies ~1 psi for every 10 degrees F change in temperature.
 

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2016 Tungsten Outback 2.5l Premium w/ES, OP 14, PP #4
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I had the TPMS low tire pressure light on with tire pressure @ 30 psi and local ambient 72°. Went out after inflating pressure 3 psi above placard pressure and driving for a short distance above 20 mph. I was surprised 30 psi would trigger a warning light. Others have reported 26 - 28 psi. I did not determine if one or more tire sensors caused the warning.
 

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'14 Subi OBW, '18 Subi Forester
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This was one of the reasons I finally decided to buy the Autel TS-408. Its a relatively low cost way to separate Sensor issues from System problems.

Lithium coin cell batteries have to provide a very short duration 'high' current pulse to power the transmitter in each tire. Maintaining voltage at sub zero F, along with the integrity of all the electronic components at low temps in the total system can become an issue in a small percentage of sensors and base receivers.
 

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2017 OB 2.5 Lim/ 2005 STI 400 WHP
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mine worked fine at -30 f in canda last week. it would bing and give me a warning as soon as i started to move but with in second would come up with accurate measurements.
 

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"mine worked fine at -30 f in canda last week."

".....can become an issue in a small percentage of sensors and base receivers."

90,000 of you will chime in that yours worked, and 7 people will report that there's did not. Such is the case with battery operated electronics at low temps.
 

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2017 Outback 2.5 Premium w/ power moonroof, dimming mirrors and power hatch. All weather package
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I got a low pressure light a week ago. Had snow over night. Got some of the snow off the car and moved the car to clear the driveway where it was parked and the warning came on and stayed on. Cleared the driveway and the rest of the car. Put the car back in it's place and went in to look at the manual. Looked at the tires. Nice and full. Let the car the rest of the day. Started it up the next morning. The low pressure warning was off and I had an email from Subaru to check the tires. Warning has not come on again.

Clearly a false warning.
 

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2017 2.5i Premium Lapis Blue
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I got a low pressure light a week ago. Had snow over night. Got some of the snow off the car and moved the car to clear the driveway where it was parked and the warning came on and stayed on. Cleared the driveway and the rest of the car. Put the car back in it's place and went in to look at the manual. Looked at the tires. Nice and full. Let the car the rest of the day. Started it up the next morning. The low pressure warning was off and I had an email from Subaru to check the tires. Warning has not come on again.

Clearly a false warning.
What were the pressures when you checked them? Or did you really just "look at them" and determine they were full?
 

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2017 Outback 2.5 Premium w/ power moonroof, dimming mirrors and power hatch. All weather package
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I just looked at them. No problem with any of them. Light has not come back on after a week and it's actually been a lot colder than it was that day.

Had the light stayed on then I would have checked them.
 

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Heck, if we all could tell the pressure in a tire by just looking at it there wouldn't have been any need to force the hassle and cost of a TPMS system on all of our new cars.
 

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One of the great things about TPMS is that it can warn you of a low tire that doesn't look low. Cold temp swings can drop tire pressure more than a lot if people realize. When all tires drop evenly it can be harder to notice than if one tire is going low because of a slow leak.

I'm pretty sure TPMS is supposed to trip when 25% of recommended tire pressure is lost. OB tires are stickered at 30 and 32, so they should signal at 24 psi (32 - 25%). There is not much of a visual difference difference between 32 and 24.
 

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Heck, if we all could tell the pressure in a tire by just looking at it there wouldn't have been any need to force the hassle and cost of a TPMS system on all of our new cars.
However it was still a false alarm and I wasn't going to go down to the gas station in the snow to top off the pressure on all 4 at 6pm and frigid cold.

That it was a false alarm will make me suspicious of other low pressure warnings unless it's obvious.
 

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However it was still a false alarm and I wasn't going to go down to the gas station in the snow to top off the pressure on all 4 at 6pm and frigid cold.

That it was a false alarm will make me suspicious of other low pressure warnings unless it's obvious.
In your case maybe it really was a false alarm. But until you check the actual pressure you don't know that for sure. You could still have one or all of your tires down 3 or 4 pounds and not know it. They might be right at the borderline of tripping the TPMS. Why not take a couple of minutes and check it with a pressure gauge and be sure?
 

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In your case maybe it really was a false alarm. But until you check the actual pressure you don't know that for sure. You could still have one or all of your tires down 3 or 4 pounds and not know it. They might be right at the borderline of tripping the TPMS. Why not take a couple of minutes and check it with a pressure gauge and be sure?
Don't have a tire pressure gauge. Never needed a pressure gauge in all the 17 years that I had an OB 2000 and that didn't have tire pressure sensors. Perhaps I'll buy one some day but it's butt freezing cold out.
 

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I try to keep our air pressures monitored - I use a cheap digital gauge. It's helpful that I also have my own air compressor in the garage. I generally check the tires when I remember, and that really isn't very often.

But the first cold-snap of the season will generally still trigger the TPMS on at least one of our vehicles. I get the gauge out and start checking tires, and it's sometimes surprising at just how low they can be. I've seen some below 20, and I've seen others right on the borderline of 24-27. It's not that easy to visually tell if they are low or not. I have a pretty good calibrated set of knuckles that I can use to push or rap on the sidewalls for a rough idea, but the gauge is the best way to verify what the TPMS is telling you.

There was one time when TPMS did save us a lot of money and time:

We were driving the Camry (long before we got an OB) on the highway, and the TPMS indicator came on. We were right at an off-ramp, so I pulled off the interstate and into the gas station parking lot at the top of the hill. I got out to check the tires and got to watch one of them (left-rear) slowly lose air. I had enough time to get out the jack and take the weight off the tire before it went completely flat. I put on the spare, check around, and went to the only tire place that was open on the holiday weekend. Turns out we got that tire fixed for free (nail), because we were national members of the club we pulled into. If the TPMS hadn't warned, I would have shredded that tire on the highway and possibly damaged the rim. The bonus was that it happened just before an exit so I didn't have to change the tire on the side of the highway approx 3 hrs from home.

I think the main reason for TPMS is 2-fold: Increased MPG from properly inflated tires, and prevention of catastrophic failure from driving on under-inflated tires. Most people have gotten used to it by now, and seem to use it simply as a reminder to add some air "soon".
 

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Discussion Starter #18
*update*
after the second day of the light being on I checked the tire pressure again. Put fronts at 35 (exactly what is called for) and rears at 34 (+1 what it is supposed to be) The light finally went out about 2 minutes into the trip.
 

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*update*
after the second day of the light being on I checked the tire pressure again. Put fronts at 35 (exactly what is called for) and rears at 34 (+1 what it is supposed to be) The light finally went out about 2 minutes into the trip.
Yours is 35F and 33R?

Mine is 32/30 (pretty sure, but I'm going by memory right now).

If TPMS should signal at -25%, and I'm assuming there's no way for the system to tell when you rotate tires front and back, then your system is probably programmed to signal at 35PSI - 25%( 8.75) = 26.25psi, somewhere around 26-27.

Do you remember what the pressures were before you topped the tires off? I'm wondering how close the numbers really were.
 
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