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I bought a car brand new 9 months ago. My tire pressure sensor came on. I checked the tire pressure, and it was at 35 PSI. My maximum tire pressure is 51 PSI with a warning not to fill above 40 PSI. I filled my tires to 40 PSI. The warning light did not go off. I then checked the car specific information in my door jam, and it says to keep my tires at 30 PSI: enter image description here

I am confused. Assuming my tires did not gain air pressure over the last 9 months, they were at least at 35 PSI when brand new.

So my tires are were at 35+ PSI when brand new, and they are at 40 PSI now. The car recommendation is 30 PSI. The tires have a max capacity of 51 PSI.

Should I let 10 PSI out of my tires? I was under the impression they were low at 35 PSI.

It is a 2015 Subaru Forester.

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You might be misinterpreting your tire pressure indicator light. Usually the light comes on when the tire pressure drops below a certain level in at least one tire. I've not heard of one responding to too high a pressure, but I suppose it's possible.

I think your pressure indicator light may be indicating a problem with the tire pressure sensor system itself. Or it could be that the overinflation of the tires is causing the system to alarm.

When the indicator comes on does it blink for a while, then turn steady? If so, you may have a problem with the system, like a defective sensor.

I usually recommend following the manufacturer's recommended tire pressure, because they've probably analyzed a lot of factors to come up with that recommendation. 30-32 is recommended by Subaru, but going to 35 is probably not going to cause a major problem. 40 may be a bit high however.

Overinflation can improve mileage, but it can also cause uneven wear, a rougher ride, and in some cases may affect handling and braking.

Also keep in mind that tire pressure changes with temperature, so if you inflate to 40 PSI cold, the pressure could be significantly higher after driving for a while.

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  • With all the ones I've dealt with, it comes on on the high side as well.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Aug 28, 2015 at 1:48
  • On my previous two cars I also had to press a button to reset the Tyre Pressure sensors after changing the pressures (i.e. letting them down a bit after carrying a heavier load or topping them up from a low pressure warning).
    – Mauro
    Aug 28, 2015 at 10:03
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If your car is relatively brand new, you may have inferred TPMS, which compares the rolling radius of each tire. If any single tire rolls more rapidly than another, then that tire must have lower pressure than the other, assuming the same tire size. This eliminates the tire pressure sensor in each wheel and its replacement upon tire replacement. So if one tire had a much higher or lower pressure than another, this could have lit up your TPMS light.

Also, if you filled your tires in the winter and not a molecule of air leaked out, they would be high in the summer. The hotter the tire, the higher the pressure.

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I just bought a 2015 Subaru Forester. I started the engine to warm it up and then checked the tire pressure meanwhile. I found each tire was overinflated 6 psi over spec so I let air out. Then the tire pressure warning was illuminated.

I fixed it by shutting off the car and then starting it back up. I don't believe U have TPMS, thus, I assume the warning light is triggered by a loss of pressure.

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