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So what's the deal? I immediately checked all the tires and they were at spec. Warning light stayed on for several days and then shut off. 2 weeks have passed and the warning showed up again. Only stayed on for a day this time. My guess is one faulty sensor.. so how do I find out which one?
 

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So what's the deal?
100% of the time when a customer complained about their low tire pressure and insisted that is was not low - the tire/tires were low. Pressure gauges may not be accurate. Yes it's possible you have a bad sensor or one with a low/bad battery. If so it takes a hand held expensive tool - to check each sensor - VIDA can not do it. I would imagine most major tires stores would have one - but as a garage owner I never wanted to spend the $2500 for that tool.
 

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When I had a bad one on my S60 I first put my winter wheels on the rear... didn’t fix it so put regular wheels on back and winters on front... gone away... then took what was left front and put it on the back... still no problem so knew it was the front right...

A lot trickier to pin down with an intermittent issue.
 

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The impending colder weather makes things more interesting, too. Lots of folks get the "message" when the temps drop below a certain range and the tires may have been near the "bottom" of the pressure range. Interesting how some vehicles will tell us which tire is the offender and some REALLY expensive cars just give the general message.
By the bye, my Black and Decker Air Station finally died after more than 15 years of faithful service. Used it mainly for bike tires; but it came in handy when time to top-off the vehicle tires. Set the desired pressure and fire it up...shuts off automatically while you are working on other tires/stuff in the garage. I wish they still made that unit.
 

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Hi. Interesting. I have had the same issues with low pressure light on/off for a while, especially recently. I pump up/check tire pressure (with an automated pump) and sometimes the light goes out after a day or so, but sometimes it stays on. Tire pressure is correct according to the air gage. So, like others asked, is it a bad sensor? I do not want to spend a lot to get that fixed. it seems like the tire pressure is fine to me though according to my gage. thoughts?
 

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Kinda like headlights. When one goes out the other one is not far behind.
These batteries (not replaceable) last 7-10 years. One is out now- maybe it's 2. If it was me - I'd replace all four of them. Check RockAuto, FCPEuro - find the VDO ones. They are OEM's. A lot less than the Volvo part.
 

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I am in the Nashville area, and the Temps have finally dropped. The local Discount Tire has a special line set up to add air because everyone is getting the tire light due to the air contracting due to lower temps. On there website it says its best to measure in the morning when the tires are cool and to add 2 lbs to the recommended when adding air in the afternoon and an extra 6 lbs. if measuring after driving on the highway for a while. https://tinyurl.com/y5txfvkk . That seem a bit extreme, I would just measure a tire that is not low and match what that number is.

On the sensors, I bought four on Amazon for my sons Nissan, said they were VDO and the light is back on after 2 years. Probably cheap knockoffs. So do not buy VDO there. On one of my other cars with OEM sensors ( Denso) tire warning just now flashed on and off on a recent trip and that car is 12 years old.
 

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I am in the Nashville area, and the Temps have finally dropped. The local Discount Tire has a special line set up to add air because everyone is getting the tire light due to the air contracting due to lower temps. On there website it says its best to measure in the morning when the tires are cool and to add 2 lbs to the recommended when adding air in the afternoon and an extra 6 lbs. if measuring after driving on the highway for a while. https://tinyurl.com/y5txfvkk . That seem a bit extreme, I would just measure a tire that is not low and match what that number is.

On the sensors, I bought four on Amazon for my sons Nissan, said they were VDO and the light is back on after 2 years. Probably cheap knockoffs. So do not buy VDO there. On one of my other cars with OEM sensors ( Denso) tire warning just now flashed on and off on a recent trip and that car is 12 years old.
I've guesstimated the difference at 10%(so....~3.5#) at normal driving temps....seems to work out for me. Roughly 40# pressure at driving temps results in 36 next morning in the garage.
 

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Don't get me started on DeflateGate! I forget whose gas law it is...
 

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It sounds like you are having a low tire due to temp changes overnight. If I recall correctly the (really basic) formula for pressure change in tires is something like 1 psi for every 10°F. I have found from my experience that on average a tire will increase about 2-4 psi from driving. I have had both my Volvo and my Honda have a low tire light on a cold morning and by the time I get to work where my tools are, light has gone out. I cannot speak for the Volvo on this, but most other manufacturers I have worked on will store a code if the light came on even if it's not still on, that code should tell you why, either low pressure, low battery, and on a couple occasions I have even seen signal interference as the cause of the code.

2009 C70 year round daily
 
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