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Well today I got in my car to go to work. As soon as I left my driveway the tire pressure sensor goes off telling me to check the front right. I drive to service station and add some air, but on visual inspection the tire looks fine and not low at all. I drive a little further and it goes off again telling me to check the front left. Once again the tire is not low and everything looks fine. How sensitive is the tire pressure sensor on this car? I have only had it go off one other time and that was while exiting one of those brushless car washes. I'm starting to think the outside air temperature is playing a large role in the problem. This morning it was a little cool (50 degrees F) compared to most mornings of around 60-65 here in Atlanta.
 

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Visual inspection tells you nothing, unless the tire is severely underpressured. Get and use a good tire pressure gauge.

I don't know how the Saab monitoring works, but on many cars what it actually "sees" is a difference in rotation between the left and right tires. This is not as good as actual pressure monitoring, but it is helpful. You may have a problem in the ABS sensor as that is used to sense the rotation. Or it may be a flat spot from sitting overnight, or something else benign.
 

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Not sure if this will help you but last week I was given a 9-7x as a loaner while the 9-3 was at the dealer. The day after I got it the low tire pressure alert went off and to make a long story short, the tires were all at 26psi (vice 32) - they told me that the alert goes off if the pressure drops below 28.

Your case sounds different though since you are alerted to the specific tire...maybe another Saab ECU hickup.
 

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The system used on the 93 was prone to problems. I think it was deleted soon after it was added. Saab used an actual pressure detecting device that was built into the back side of the (special) valve stem. In addition to being overly sensitive, this monitoring device could break off and bounce around inside the tire.

A few people inquired about adding this to earlier or later models, and the consensus here was don't bother.
 

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we've got a system on our Honda Pilot.

Every year when the temp starts dropping into the 40's, we have to add a pound or two. they are fairly sensitive.

I am guessing it is just a temperature thing.
 

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For every 10 degrees of ambient temperature drop, your tire pressure drops 1 psi.

Of course, heat is generated as you drive, so this complicates things, but at least at cold startup your pressure will be lower at lower temps.
 
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