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Low tire pressure warning light-Can cold weather affect?

Discussion in 'Gen II Prius Care, Maintenance and Troubleshooting' started by gh4chiefs, Nov 2, 2007.

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  1. gh4chiefs

    gh4chiefs New Member

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    Good morning,

    I'm kind of grasping at straws here, hoping that I'm not actually getting a flat, but I thought I'd throw this out there. I had to leave the office briefly this morning and as I went just a little ways, I noticed the low tire pressure warning light was on. Well I'm like "Oh crap, I'm getting a flat" because the last time I got that light, I did indeed have a flat and it was very noticeable.

    So I pull over, I didn't check any pressure but visibly inspected all 4 tires and no sign of a flat or even a low tire. So I go take care of my business, come out, still no flat, but the light is still on. I get back to the office, check my tires again, still no sign of a flat or even a low tire.

    So my question is, it's 32 degrees here this morning, so is it possible the cold air temp is giving me a "false positive" or do I probably just have wishful thinking?
  2. john1701a

    john1701a Prius Guru

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    Low pressure warning lights are designed to indicate when pressure is 25% lower than the minimum required. That's a very squishing tire. You're in the danger zone at that point.

    For Prius, that would be around 26 PSI... way too low and far more than any affect the cold would normally have, which is 1 PSI for every 10 F degree drop. So you now have yet another reason to run your tires at a higher PSI. The favorite is 42/40 (front/back PSI). I personally prefer 44/42.

    As for having a flat, the tire was probably just soft in the first place. Pump in up beyond the minimum 35/33, then check it from time to time to see if there is a leak or not.

    Lastly, always check pressure when the tires are cold. Warmed air (above the outdoor temperature) inside causes overinflated (bad pun) readings.
  3. galaxee

    galaxee mostly benevolent

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    cold weather= low tires. check your pressures, you'll probably find them all a little low.
  4. gh4chiefs

    gh4chiefs New Member

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    Thanks John,

    Well I probably have a leak on one of them then. Maybe at lunch, when I have some time, I'll go out and check tire pressures with a guage.

    I've noticed for some time that all 4 tires seem to have a hard time "staying up to pressure." I'll air them up to the 42/40 specs that I've seen recommended here, and they won't stay. But yet they don't go flat, so I finally gave up on that.

    But I haven't checked in awhile, so maybe they're all low and just don't look it.

    But odds are, I probably do have an actual leak.

    Thanks.

    <div class='quotetop'>QUOTE(galaxee @ Nov 2 2007, 09:17 AM) [snapback]533841[/snapback]</div>

    Well they probably are low. As mentioned in my previous post, they seem to want to "leak" all the time as I can't keep them up to 42/40 specs. And it's not just one, they all seem to go down in pressure.

    It's kind of weird, IMHO. I've never had tires that wouldn't stay up.
  5. efusco

    efusco Troll Slayer Staff Member

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    I picked up a nail recently that resulted in a slow leak. I noticed that one tire looked slightly lower than the rest and decided to check the pressure...it was at 20psi...and I run mine at 50f/48r usually...so even more than 50% low on pressure I could barely tell on visual inspection.

    Any time the average daily temp drops by more than 10 degrees it's a good idea to recheck your tire pressure and top them up at least to manufacturer's rec. 35/33, better yet 42/40 for better handling, tire wear and FE.
  6. gh4chiefs

    gh4chiefs New Member

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    Well this is very odd indeed. I took the car out at lunch and aired up all the tires. Before I aired them up, I checked all of them, and got a reading of 35 pretty much all the way aroudn. So I decide to air them to 42/40 and when I go back to put air in the left rear tire, I'm suddenly getting a rating of 15. :eek:

    So I aired it up to 38 (when the machine shut down :angry: ) and we'll see what happens. I'm guessing I have a nail or something in that tire. I don't understand why I got a reading of 35 the first time though.
  7. topkick

    topkick Member

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    In the past two months I have had a screw in my right rear tire and a nail in my right front tire. The low pressure feature works well on the prius, the only fault I have with it is there is no indication of which tire is low, but not hard to figure out (with a guage).

    The other morning I got the low presure light again and was really unhappy, I have not had a nail or other object in my tires for many years (and now was three times in two months, I thought). I found that the right front tire was low so I took it off and checked the to find where I had a problem and could find nothing obvious.

    In the six months that I have had the Prius the tires have not held pressure like other tires that I have had (not counting the screw and nail). So I took a little water and checked the valve stem, there WAS a leak at the stem. I went to PepBoys and bought a valve stem tool. I was able to turn the valve stem on all four tires almost a full turn and it did not feel over tightened. Now they seem to stay at the pressure I set them at.

    So if your tires are not holding pressure as well as you think they should check the valve stems.
  8. gh4chiefs

    gh4chiefs New Member

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    Thanks topkick, they definitely won't hold pressure. I'll give that a try.
  9. drifty1955

    drifty1955 New Member

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    Same here. I finally listened to everyone here and brought my 07's stock tires up to 42-40 quite a while back. Got an immediate 8 mpg boost. But 2 weeks later I checked them again and all tires were down to 36 pounds. I knew something was up because the steering started doing that "constantly have to correct" thing. Seems these Integritys are about as tight as a WWII submarine. These tires suck. You must check them once a week.Gonna get me a little air compressor for home. Got a big 150 lb one but too loud to fire up all the time.
    This car has a learning curve for alot of things. I just recently after 2 months have mastered the pulse & glide and consumption meter went from showing a never changing 47 mpg's to now showing 55. I am now able at the end of my commute late at night to go full EV for about 2 miles snaking silently and slowing through the back suburbs to my house. Its alot of fun. This car has changed my whole attitude about commuting & driving in general. I drive alot slower & smarter than I ever have and now notice how everyone drives as fast as they can up to the light that they all saw 2 blocks away was red just to all slam on there brakes. Can you imagine that one simple principle if changed by the general population could save millions of gallons of gas annually. Everyone is in such a freaking hurry just to sit at the light. Just drive smarter.
  10. drifty1955

    drifty1955 New Member

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    <div class='quotetop'>QUOTE(Drifty'sDad @ Nov 3 2007, 02:07 AM) [snapback]534237[/snapback]</div>


    Oh and temp had nothing to do with tires leaking air. Has been hot as hell.
  11. No-Start

    No-Start New Member

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    <div class='quotetop'>QUOTE(gh4chiefs @ Nov 2 2007, 12:52 PM) [snapback]533979[/snapback]</div>

    Be careful about over tightening your valve stem on TPWS sensors. If you overtighten them, they could seize up, which could become an issue later on, as you'll have to replace them

    There is a tool for tightening them that has a preset torque value. Not too many places have it.

    No-Start.
  12. stukid

    stukid New Member

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    There is a direct correlation between tire pressure and temperature.
    In physics, its called the "temperature pressure relationship."
    The TPWS only monitors pressure, not ambient temperature, so in answer to your question-yes.
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