-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Model 3 TPMS sensors are junk
- Thread starter voip-ninja
- Start date
He's also in SW Florida. I've been to St. Pete & Tampa many times, it's never cold there.
Cold is relative, especially when taking about pressure changes
. Admittedly, a 30 degree shift above zero produces less of a pressure change than a 30 degree shift below zero...
comanchepilot
Member
can't you go into the vehicle settings menu and reset the TPMS like you either rotated the tires or got new ones like every other TPMS sensor? Set the air pressure and it'll assume the tire pressure is what it says on the vehicle door sticker and take it from there - thats how its supposed to work - which is why tire places verify the airpressure when they put on new tires.
SomeJoe7777
Marginally-Known Member
Ya, the issue here is altitude. Looks like the Tesla isn't compensating for the lower air pressure vs. the TPMS absolute pressure readings.
You need to get the service guys at a Tesla service center to escalate the problem to engineering. It will have to be fixed in software. There's nothing the TPMS modules or TPMS system can do about it.
For those who may not be familiar with what's happening, the problem arises because tire pressures are specified as a relative pressure -- i.e. a differential pressure between the air inside the tire and the air outside. The standard tire pressure gauge measures exactly this, using the air from the tire through the valve stem, and the air outside.
However, TPMS modules have no source for the outside air. So they have to measure an absolute pressure using an internal reference. The internal reference is calibrated to sea level.
So, let's say we have a tire inflated to 45 psig (psi by gauge) at sea level. 45 psi is the difference between the absolute pressure inside the tire (59.7 psia) and the absolute pressure outside the tire (14.7 psia -- atmospheric pressure at sea level).
Now we drive to 10,000 feet elevation. Up here, the atmospheric absolute pressure is 10.1 psia. Assuming the tire has no leaks, the inside air pressure is still 59.7 psia, resulting in a tire gauge pressure reading of 59.7-10.1 = 49.6 psig. The tires are now overinflated, so you need to reduce air pressure. But the TPMS module still reads 45 psi because the inside air pressure of 59.7 psia is still exactly 45 psi over the TPMS sensor's internal reference of sea level pressure (14.7 psia).
So you drop the tire pressure back to 45 psig by the tire pressure gauge, resulting in an internal tire pressure of 55.1 psia. Now the gauge reads 55.1-10.1 = 45 psig which is perfect. But TPMS now says the tire is at 55.1-14.7 = 40.4 psig and you're close to setting off the low pressure alarm.
Telsa needs to compensate by using the map, looking up the elevation, then looking up the expected atmospheric pressure at that altitude, find the difference between that pressure and sea level pressure, and then add that offset to the TPMS readings before displaying the value and before comparing the reading with the alarm threshold. This will result in TPMS readings that are very close to the gauge pressure.
You need to get the service guys at a Tesla service center to escalate the problem to engineering. It will have to be fixed in software. There's nothing the TPMS modules or TPMS system can do about it.
For those who may not be familiar with what's happening, the problem arises because tire pressures are specified as a relative pressure -- i.e. a differential pressure between the air inside the tire and the air outside. The standard tire pressure gauge measures exactly this, using the air from the tire through the valve stem, and the air outside.
However, TPMS modules have no source for the outside air. So they have to measure an absolute pressure using an internal reference. The internal reference is calibrated to sea level.
So, let's say we have a tire inflated to 45 psig (psi by gauge) at sea level. 45 psi is the difference between the absolute pressure inside the tire (59.7 psia) and the absolute pressure outside the tire (14.7 psia -- atmospheric pressure at sea level).
Now we drive to 10,000 feet elevation. Up here, the atmospheric absolute pressure is 10.1 psia. Assuming the tire has no leaks, the inside air pressure is still 59.7 psia, resulting in a tire gauge pressure reading of 59.7-10.1 = 49.6 psig. The tires are now overinflated, so you need to reduce air pressure. But the TPMS module still reads 45 psi because the inside air pressure of 59.7 psia is still exactly 45 psi over the TPMS sensor's internal reference of sea level pressure (14.7 psia).
So you drop the tire pressure back to 45 psig by the tire pressure gauge, resulting in an internal tire pressure of 55.1 psia. Now the gauge reads 55.1-10.1 = 45 psig which is perfect. But TPMS now says the tire is at 55.1-14.7 = 40.4 psig and you're close to setting off the low pressure alarm.
Telsa needs to compensate by using the map, looking up the elevation, then looking up the expected atmospheric pressure at that altitude, find the difference between that pressure and sea level pressure, and then add that offset to the TPMS readings before displaying the value and before comparing the reading with the alarm threshold. This will result in TPMS readings that are very close to the gauge pressure.
Last edited:
eprosenx
Active Member
FYI, I find this discussion here very valuable. It helps inform folks that there might be an issue and gives folks a place to share stories and perhaps make guesses as to what is going on. I have learned something!
This keeps manufacturers from keeping consumers in the dark. Tesla in general has been pretty good about being above board, but the Internet is good for keeping everyone honest. You can't hide issues anymore.
All they have to do to “solve” this problem is lower the stupid TPMS warning threshold. That warning should be that you have a low or flat tire, not that you have the audacity of using a few more electrons to make your trip.
The threshold is federally mandated (FMVSS 138) to be a 25% maximum drop from the placard pressure. Depending on the SW/ HW set up, you may need to drive a bit to get the warning to reset after your temperature compensation inflation.
Stellavator
Member
The solution is to allow the user to reset the notification based on your preferred tire pressure. Like how it works in every other car. Fill tire, press button, system resets to the new pressure as the proper pressure, and then warns you when it drops from there.
timk225
Active Member
I've compared my TPMS display to a digital air pump and my own cheap tire gauge, they were within 1 psi or so.
The low pressure warning shouldn't be going off at 37 -38 psi, as it has done for me. 32-34 would be more realistic.
If the federal mandate is a 25% drop from normal tire pressure at 45 psi, then that'd be 33.75 psi.
The low pressure warning shouldn't be going off at 37 -38 psi, as it has done for me. 32-34 would be more realistic.
If the federal mandate is a 25% drop from normal tire pressure at 45 psi, then that'd be 33.75 psi.
Stellavator
Member
Fine. How it SHOULD work on every other car. If it does not work that way, it is a design failure.
Ludalicious
Active Member
Had this issue the other day with my S. Left it outside my garage over night and it's fairly cold now. Set off 2 pressure sensors. This happens when it gets cold outside. Especially when you are using air in tires. Fairly common problem. If you don't want to have this issue with temperature change and loosing air. Get nitrogen installed in the tires. You won't have the issue again.
(First is that nitrogen is less likely to migrate through tire rubber than is oxygen, which means that your tire pressures will remain more stable over the long term. Racers figured out pretty quickly that tires filled with nitrogen rather than air also exhibit less pressure change with temperature swings.)
If it does work that way, it violates federal requirements and the reasoning behind the limits/ TREAD act.
One edge case is OEM tested and certified wheel sets that use different pressures like the Model X 20 vs 22 inch (40 vs 42 PSI), I believe this is tied to the vehicle config/ IC image.
So this is what I had for the first six miles of my drive this morning, finally they did clear, but this is still bogus in my opinion. The car is putting a low pressure warning out right on the 39-40 psi bubble and that's absurd if the standard tire pressure is 45 psi.
Was the right rear throwing an error before that last fill? I'm wondering if it hysteresis for over/ under.
Similar threads
