Tire pressure low, but tire pressures look normal.

boeing82

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#1
Hi,
I'm getting a low tire pressure indicator intermittently, but the tire pressures are all the same, and appear to be normal (the error I was getting was for the rear left tire). Has this happened to you? What do you recommend? What might cause this?
Thanks for any insight!
IMG_9433.jpg
 

SoFlaModel3

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#2
How long were you driving when this appeared? Tire pressure levels are presented as cold temperature so you may be a pinch low if that's a warm temperature. Odd yes that only one tire triggers it but I have seen that before.
 
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#3
I get this all the time too, except it's for my rear right tire. Tire pressure can be anywhere from 41-38, and even if all 4 are the same it'll say just that tire is low. Super annoying. Also, does there need to be THREE freaking alerts on the screen for something as minor as low tire pressure??
 

mswlogo

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#4
How long were you driving when this appeared? Tire pressure levels are presented as cold temperature so you may be a pinch low if that's a warm temperature. Odd yes that only one tire triggers it but I have seen that before.
That's on the hairy edge of being low at cold PSI too.

I tried lowering my tires to 39 psi cold. They all alarmed. And they were not happy until they got back to 42, and even then it took a while.

The TPMS system is a bit odd. It probably uses the Neural Net processor to figure out if a tire is low (you know, the one that decides when to wipe or when to lower high beams). ;)
 

TheMagician

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#5
This is arguably the smartest car on the road. Don’t understand why the TPMS trigger setting isn’t user selectable (down to whatever is probably a federally mandated lower setting). Even if that’s not possible, why not just lower it before it gives a warning. I’ve never seen such a temperamental system. My Leaf has a 36 psi recommended setting and easily has to be below 28 to trigger a warning (I’m going from memory so don’t bust on me if it’s 29 or 30).
 

Feathermerchant

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#6
There is a federally mandated setting which (I think) is 20% below MFR recommendation.
Remember to set the tire pressure COLD. That is after the car has been idle for long enough for the tire temperature to equal the ambient air temperature. Say 5 to 8 hours.
So if the door tag says 42 then set them at 42 COLD. NEVER let air out to lower the pressure on a warm tire.
 

boeing82

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#7
How long were you driving when this appeared? Tire pressure levels are presented as cold temperature so you may be a pinch low if that's a warm temperature. Odd yes that only one tire triggers it but I have seen that before.
This was fairly soon upon starting the car, and it was in the 40s outside.

I guess from a user experience standpoint, we should be getting an error only if the number is different from others. It feels odd to get an error for my left rear tire at 41 that I don't get for my right rear tire at 41.
 

Ed Post

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#9
Here's my experience:

1) The TPMS reads absolute pressure, a tire gauge reads pressure relative to outside air pressure. If you are at altitude (like up here in Denver), TPMS will read lower. Usually 3 PSI lower at 5000 feet. If you go into a tire store up here, you need to ask them to fill to 45 to get the TPMS number above 42.
2) Of course the tire pressure is lower when colder, and goes up after the tires get warm.
3) The car applies hysteresis to the readings to issue the warning. If the pressure ever measures below 40 on any tire, it doesn't turn off the warning until such time as you get in the car, put it in drive, and all four tires are above 42.