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2016 Tungsten Outback 2.5l Premium w/ES, OP 14, PP #4
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Discussion Starter #1
Low tire pressure monitoring light came on recently. Found all four tires 30 psi or above. Ambient was in low 70's. Later checked spare. Found at 30 psi. There's some forum discussions suggesting the spare might have a sensor however after inflating back to 60 psi warning light did not go off after driving. I don't routinely check the spare's pressure because I have a 12v compressor in the car and it's a booger to do the way the spare is mounted. Is there any info the spare does or does not have a pressure sensor?
I've read a few reports of false warnings but generally it's been in cold weather. I experienced a false warning but it was 30° at the time.
Any case looks a trip to the dealer is in my future.
 

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2008 Subaru Tribeca
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No tpms in the spare, bump up your tires to 36 in the winter and be done with the light, unless you have a leaking tire.
 
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2017 2.5 Touring
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Found all four tires 30 psi or above. Ambient was in low 70's. Later checked spare. Found at 30 psi.
At least the light got you to check and inflate your spare tire.
Put you tires at least to 34 or 35.
Light will likely go out and save you taking it to the dealer.
 

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TPMS doesn't like 30 psi. All 4 of mine were at 30 when TPMS light came on. I was getting ready to check and reset any way. I run 36 front and 34 rear on all my outbacks.
 

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TPMS doesn't like 30 psi. All 4 of mine were at 30 when TPMS light came on. I was getting ready to check and reset any way. I run 36 front and 34 rear on all my outbacks.
Yes. Put tires to AT LEAST what it says on the drivers door, or you will be posting about how few miles you got out of them.
 

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2016 Outback Premium 2.5 CVT w/EyeSight+SRVD
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Low tire pressure monitoring light came on recently. Found all four tires 30 psi or above. Ambient was in low 70's.
...
I experienced a false warning but it was 30° at the time.
Tire pressure drops ~1 psi per 10° F drop in temperature. Thus: 30 psi @ 70° F = ~26 psi @ 30° F. (Pressure also varies slightly with altitude/elevation, but we will ignore that in this discussion.)

Tire pressures should be set based on the coldest operating temperature commonly expected. Based on our local climate, I typically set winter tire pressures for 30° F and summer for 70° F.

Winter example: Our 2016 Outback (OE tires), is placarded for 35F/33R. After allowing the car to sit garaged overnight at an ambient temperature of 60° F, I will set the tire pressures to 38F/36R using an accurate gauge. That will give me ~35F/33R at 30° F, and ~33F/31R at 10° F.
 

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2016 Tungsten Outback 2.5l Premium w/ES, OP 14, PP #4
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Discussion Starter #7
After posting this I decided to bump up pressures to what I generally run, namely 38/35. I hadn't driven the car in awhile, thus not checked tire pressures recently, but went to a nearby hiking trailhead. Warning light came on during return trip home. The warning light did go off at these pressures, namely 38/35.
There is not a specific pressure defined in the OM that triggers when a warning comes on. Words such as "significantly" under pressure and "severely" low are used. I never associated 30 psi as meeting either of those definitions.
Thanks for the responses
 

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2013 OB 3.6R (former)
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Sharp temperature changes may cause it. So, if you bumped them up when it was quite warm, especially if car had been outside, and then it got a lot colder, it can cause the light to come on.

AND/OR you can have a leaking tire, as mentioned.

On my car, the light comes on at around 28 psi. I would not run 38/35 on P-metric tires. It is way too much for a comfortable ride and the center is probably wearing faster than the edges. I run 33/31 and I am fine with comfort and pressures. I run my KO2s at 39 though (previously even at 44) but they are LT.
 

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'14 Subi OBW, '18 Subi Forester
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Generally, 20% below the B-Pillar recommendation is the trip point. That's 6-7 below in most use cases for the Outback.
 

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2017 Outback, 2.5L, Auto; 2018 Forester, 2.5L, Auto (for Mama); 2005 Baja, 2.5 Turbo, Manual
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No tpms in the spare, bump up your tires to 36 in the winter and be done with the light, unless you have a leaking tire.
That's what I thought, but on recent trip TPMS light came on while all four tires were 32/33psi. When we got home I found the spare low. Airing it up turned the TPMS light off. Coincidence? Or update for 2017?
 

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Mine came on at 27. Bumped it up to 33 all round and it went off. I don't bother with inflating different pressure (front/rear) too difficult to maintain and I have a hard time believing it makes a difference.
 

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I'm still going to say coincidence.

Some vehicles with a full size spare are set up for the entry of 5 TPMS sensors. The spare tire in not in motion, so it would go into deep sleep and cease transmitting. Those systems are programmed that if they see 4 of the 5 talking, they are happy. If you rotate in the spare, the spare starts transmitting and the tire taken off the vehicle goes to sleep. You still have 4 pieces of valid data, and the 'new' spare is out of the picture. And again, all those 5 tires are at the exact same pressure. You don't have a skinny high pressure spare involved.
 

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Mine came on at 27. Bumped it up to 33 all round and it went off. I don't bother with inflating different pressure (front/rear) too difficult to maintain and I have a hard time believing it makes a difference.
Two reasons to respect the manufacturers recommendations about front to rear pressures:

The front-heavy vehicle puts more weight on the fronts, creating a slightly larger flat spot and this a slight difference in rotational circumference. The staggered pressure helps even out the distance traveled with each revolution, and thus decreases wear on your center differential as it fights to do the same mechanically.

A slight increase in contact patch in the rear helps with trailing throttle oversteer.
 
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My Ford explorer called for 30 front 35 rear. When I would go to the Ford dealer to rotate the tires, they would do so and not adjust the pressure. So I would have 35 lbs on one diagonal (front pass, rear driver) and 30 on the other diagonal (front driver, rear pass). I got fed up and I now keep them all at 33. Same on my '16 Outback.
 

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As I said above, it's your transmission and your safety.
 
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2008 Subaru Tribeca
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Coincidence id say.
 
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