Tire Pressure Issue - TPMS
04-01-2017, 09:05 PM
#1
Instructor
Thread Starter
Tire Pressure Issue - TPMS
Hi All,
Can someone please explain the TPMS to me like I'm 4. For the last two weeks I've come out to my car saying -6 on the driver rear. First I thought maybe I had a leak so check the pressure and it was at about 31psi (cold) went and filled it up (it didn't want to take air the first place) so went to a shop (repair shop not tire as it was the closest) and had them fill fronts to 32psi and rear to 36psi (that was 3 days ago).
I've checked it with a gauge over the last 2 days (still 36psi cold) yet the TPMS is still saying -6. Now, I've ready a number of threads and I've already reset by going to winter/summer and changing the size. I drove till it resets, and once it resets it show 36psi and all is good until I turn off the car, then it goes back to -6. My car is a '14 so the batteries should still be good.
I emailed the dealer thinking maybe the sensor is bad, and this is the reply I got (I don't understand what he is saying by "reset the gauge" unless he's saying to fill the tire to 41psi?)
Dealer: "Best thing to do is listen to the gauge, and go against our normal thought process. So if the gauge reads 35psi, but it shows -6, make the gauge read 41psi, or whichever equivalent the car is asking for. The optimum thing to do is get the fill gauges as close to 0 as possible. When driving, the tires heat up, so the gauge will often begin to register a few extra pounds of air."
Can I reset/calibrate the TPMS somehow to match what the tire is actually set at?
Sorry for the long post...
Can someone please explain the TPMS to me like I'm 4. For the last two weeks I've come out to my car saying -6 on the driver rear. First I thought maybe I had a leak so check the pressure and it was at about 31psi (cold) went and filled it up (it didn't want to take air the first place) so went to a shop (repair shop not tire as it was the closest) and had them fill fronts to 32psi and rear to 36psi (that was 3 days ago).
I've checked it with a gauge over the last 2 days (still 36psi cold) yet the TPMS is still saying -6. Now, I've ready a number of threads and I've already reset by going to winter/summer and changing the size. I drove till it resets, and once it resets it show 36psi and all is good until I turn off the car, then it goes back to -6. My car is a '14 so the batteries should still be good.
I emailed the dealer thinking maybe the sensor is bad, and this is the reply I got (I don't understand what he is saying by "reset the gauge" unless he's saying to fill the tire to 41psi?)
Dealer: "Best thing to do is listen to the gauge, and go against our normal thought process. So if the gauge reads 35psi, but it shows -6, make the gauge read 41psi, or whichever equivalent the car is asking for. The optimum thing to do is get the fill gauges as close to 0 as possible. When driving, the tires heat up, so the gauge will often begin to register a few extra pounds of air."
Can I reset/calibrate the TPMS somehow to match what the tire is actually set at?
Sorry for the long post...
04-01-2017, 09:35 PM
#3
Instructor
Thread Starter
04-01-2017, 10:50 PM
#4
04-01-2017, 11:05 PM
#5
Instructor
Thread Starter
It was already on that setting so I switched it to full load and then back the second time, waited for it to "learn" as I drove around and same result, -6 next time I started the car
04-01-2017, 11:33 PM
#6
Rennlist Member
I'm not sure from your posts, but you are looking at readings that present two different concepts but you use them interchangeably. I apologize if you already understand this but just to be sure, here's the difference:
When you see 36, you are looking at the absolute tire pressure reported by the tire regardless of temperature and tire selections on the TPMS. This typically increases as you drive and the tire gets warmer. Outdoor ambient temperatures can also have an effect, like when tire pressures decrease when the weather gets colder and the car is parked.
When you select Fill Info on the MFD (and you can only do this with the car sitting still), the car now provides a relative air pressure based upon its interpretation of the tires current operating temperature, the Full Load vs Partial, Comfort/Not, and tire type/size settings, and the current air pressure in the tire. If this reads -6 when the tires are cold at some pressure, let's say 31, and you don't change any settings and drive the car to heat the tires up, the reading should still read -6 even if the heated air in the tire has now risen to an absolute pressure of 35. This holds true with a 0 reading under fill info as well and this is what you shoot for. Once you get the tire adjusted to read 0, it will stay at 0 or really darned close regardless of whether the tire is hot or cold and given that you aren't changing settings in the MFD.
So if the Fill Mode readout says -6, you need to and 6 pounds of air to whatever reading you get from either the car's absolute temperature gauge or from your handheld gauge. If the handheld gauge reads 31, then add air until it reads 37. Once you do then the Fill Mode readout should read zero or real close to that. You can then add or remove a little air to get it nailed at zero all around if you want. I'm usually happy at zero or +/-1. At the point, it is just an interesting curiosity as to what the absolute readout says... or if they read significantly differently from side to side as you are driving that is also cause for real concern since one of the tires is deflating.
Did this help?
When you see 36, you are looking at the absolute tire pressure reported by the tire regardless of temperature and tire selections on the TPMS. This typically increases as you drive and the tire gets warmer. Outdoor ambient temperatures can also have an effect, like when tire pressures decrease when the weather gets colder and the car is parked.
When you select Fill Info on the MFD (and you can only do this with the car sitting still), the car now provides a relative air pressure based upon its interpretation of the tires current operating temperature, the Full Load vs Partial, Comfort/Not, and tire type/size settings, and the current air pressure in the tire. If this reads -6 when the tires are cold at some pressure, let's say 31, and you don't change any settings and drive the car to heat the tires up, the reading should still read -6 even if the heated air in the tire has now risen to an absolute pressure of 35. This holds true with a 0 reading under fill info as well and this is what you shoot for. Once you get the tire adjusted to read 0, it will stay at 0 or really darned close regardless of whether the tire is hot or cold and given that you aren't changing settings in the MFD.
So if the Fill Mode readout says -6, you need to and 6 pounds of air to whatever reading you get from either the car's absolute temperature gauge or from your handheld gauge. If the handheld gauge reads 31, then add air until it reads 37. Once you do then the Fill Mode readout should read zero or real close to that. You can then add or remove a little air to get it nailed at zero all around if you want. I'm usually happy at zero or +/-1. At the point, it is just an interesting curiosity as to what the absolute readout says... or if they read significantly differently from side to side as you are driving that is also cause for real concern since one of the tires is deflating.
Did this help?
04-01-2017, 11:55 PM
#7
Instructor
Thread Starter
I'm not sure from your posts, but you are looking at readings that present two different concepts but you use them interchangeably. I apologize if you already understand this but just to be sure, here's the difference:
When you see 36, you are looking at the absolute tire pressure reported by the tire regardless of temperature and tire selections on the TPMS. This typically increases as you drive and the tire gets warmer. Outdoor ambient temperatures can also have an effect, like when tire pressures decrease when the weather gets colder and the car is parked.
When you select Fill Info on the MFD (and you can only do this with the car sitting still), the car now provides a relative air pressure based upon its interpretation of the tires current operating temperature, the Full Load vs Partial, Comfort/Not, and tire type/size settings, and the current air pressure in the tire. If this reads -6 when the tires are cold at some pressure, let's say 31, and you don't change any settings and drive the car to heat the tires up, the reading should still read -6 even if the heated air in the tire has now risen to an absolute pressure of 35. This holds true with a 0 reading under fill info as well and this is what you shoot for. Once you get the tire adjusted to read 0, it will stay at 0 or really darned close regardless of whether the tire is hot or cold and given that you aren't changing settings in the MFD.
So if the Fill Mode readout says -6, you need to and 6 pounds of air to whatever reading you get from either the car's absolute temperature gauge or from your handheld gauge. If the handheld gauge reads 31, then add air until it reads 37. Once you do then the Fill Mode readout should read zero or real close to that. You can then add or remove a little air to get it nailed at zero all around if you want. I'm usually happy at zero or +/-1. At the point, it is just an interesting curiosity as to what the absolute readout says... or if they read significantly differently from side to side as you are driving that is also cause for real concern since one of the tires is deflating.
Did this help?
When you see 36, you are looking at the absolute tire pressure reported by the tire regardless of temperature and tire selections on the TPMS. This typically increases as you drive and the tire gets warmer. Outdoor ambient temperatures can also have an effect, like when tire pressures decrease when the weather gets colder and the car is parked.
When you select Fill Info on the MFD (and you can only do this with the car sitting still), the car now provides a relative air pressure based upon its interpretation of the tires current operating temperature, the Full Load vs Partial, Comfort/Not, and tire type/size settings, and the current air pressure in the tire. If this reads -6 when the tires are cold at some pressure, let's say 31, and you don't change any settings and drive the car to heat the tires up, the reading should still read -6 even if the heated air in the tire has now risen to an absolute pressure of 35. This holds true with a 0 reading under fill info as well and this is what you shoot for. Once you get the tire adjusted to read 0, it will stay at 0 or really darned close regardless of whether the tire is hot or cold and given that you aren't changing settings in the MFD.
So if the Fill Mode readout says -6, you need to and 6 pounds of air to whatever reading you get from either the car's absolute temperature gauge or from your handheld gauge. If the handheld gauge reads 31, then add air until it reads 37. Once you do then the Fill Mode readout should read zero or real close to that. You can then add or remove a little air to get it nailed at zero all around if you want. I'm usually happy at zero or +/-1. At the point, it is just an interesting curiosity as to what the absolute readout says... or if they read significantly differently from side to side as you are driving that is also cause for real concern since one of the tires is deflating.
Did this help?
Your saying if the car is saying -6 and tells me the psi is currently at 30psi (even though a hand held gauge says 36) that I need to put air in my tire until it gets to 0 or 36psi, even if my tire is already at 36psi (meaning I need to fill it to 42psi) and then let air out until I have 36psi? Won't the car just read the deflating psi and go back down?
This seems so crazy, why wouldn't it just read the actual psi like the hand gauge?
I'm sure you already understand what I was saying but just to confirm. My hand held gauge says my psi is 36, yet the car is saying it is 30 (thus the -6) all my other tire read correct on the TPMS to the actual hand gauge, it's only the driver rear that reads incorrect and it's been fine for over a year with no change to any of the tires. For some reason it's now 6psi off?
Last edited by Austin-Guy; 04-02-2017 at 12:19 AM.
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04-02-2017, 01:01 AM
#8
Rennlist Member
Sounds like a bad TPMS sensor. Confirm the year of the car and how old the TPMS sensors are. Our '08 Cayman started acting up similarly with one tire, then the rest being off around the six year point. Had them all replaced and no issues since 2013. The '14 991 has no issues with the display vs. tire gauge when cold.
If you select comfort pressures you are limited to 165 mph-shouldn't be an issue, but something to be aware of.
If you select comfort pressures you are limited to 165 mph-shouldn't be an issue, but something to be aware of.
04-02-2017, 06:46 AM
#9
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This ----^
If ONE tire shows 36 on a hand-held and -6 on the MFD, and the other three show X,Y,Z on a hand-held and the same X,Y,Z on the MFD, then then sensor on the first tire is wacky. Provided ...
... that you are taking the measurements at the same time.
Alternatively, I can interpret the posts thusly: "On day one, I mess with air pressure and TPMS settings and all is well. Then the next day, one tire is -6."
If the above is correct then the one tire might have a leak.
If ONE tire shows 36 on a hand-held and -6 on the MFD, and the other three show X,Y,Z on a hand-held and the same X,Y,Z on the MFD, then then sensor on the first tire is wacky. Provided ...
... that you are taking the measurements at the same time.
Alternatively, I can interpret the posts thusly: "On day one, I mess with air pressure and TPMS settings and all is well. Then the next day, one tire is -6."
If the above is correct then the one tire might have a leak.
04-02-2017, 06:58 AM
#10
Rennlist Member
I promise I wasn't just trying to be difficult in my first post!
So with a reliable handheld gauge reading 36 on the tire at the same time the car's is reading 30 I agree with Pavegeno928 it is likely to be a problem with the in-tire sensor, which should have lasted at least 5 years. The thing about the shop you visited that set the tire to 36 PSI is they would have likely done that with the tire warmed up, so once the tire cooled off again I'd expect it to read 3 or 4 pounds less. A drop of 6 is a lot unless you were doing autocross-stye slaloms back and forth to the shop!
The only way I can think of to 100% confirm it is the TPMS sensor is to confirm that your handheld gauge reads 36 on both rear tires while the absolute pressure readout in the car reads 30 on one and 36 and the other. That removes any doubt in my mind... and there is very little of that in the first place.
One thing the dealer can do that you can't is to read the battery-life-remaining report from the TPMS. This is being reported by the sensor but we have no way to see it. Apparently they don't like to display it since I've been told the readout is very non-linear and the months remaining can remain quite high until near the end and then it plunges quickly.
In any case, if the hand-held gauge test confirms the sensor is bad with that side-to-side test, regardless of battery life, it will have to be replaced.
04-02-2017, 11:13 AM
#11
Rennlist Member
Bottom line: If your TPMS ever deviates 6 psi from a good hand held gauge you need to see the dealership (or wherever you get your car repaired).
Been there, done that
Been there, done that
04-02-2017, 04:51 PM
#12
Instructor
Thread Starter
So is this in a location that can be patched/plugged?
04-02-2017, 04:54 PM
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Yes, that can be plugged/patched.
$64,000 question: is that the tire the TPMS is complaining about?!?
$64,000 question: is that the tire the TPMS is complaining about?!?
04-02-2017, 05:06 PM
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I think your TMPS mystery has been solved: It was doing its job 