BigEarl

So it's finally cold enough to where it affects tire pressure. I had a light cause the front left was 27 (the rest were at 28). I added air, started car and hit the reset button under dash. The data clears, it runs its diagnostic and sees that is has the same as other 3 tires but still trips light. I've tried resetting it multiple times.


Anybody else seen this? Something I'm doing wrong. It's a 2015 Fsport awd.

Thanks!!

4TehNguyen

iTrader: (1)

drive around and it goes away. Reset button under the dash is for using another set of TPMS i believe

mjeds

4TehNguyen is correct the "reset" button is for when you move the TPMS (rotate the tires) or replace them.

you need to drive the car and heat up the tires for it to update the display. and I would check your door sticker for the proper inflation at cold temp, as I believe it should be 36psi cold., (car sitting for 4 or more hours) 28psi is way too low, 95% of the cars today sit between 32psi and 36psi cold.

4TehNguyen

iTrader: (1)

believe its 35/37 front rear on F Sport

BigEarl

thanks. i might have my numbers wrong and pulled 27/28 out of the air, but this still doesn't sound right. All 4 tires are currently at the same PSI but only one tire is showing an issue? I don't see what driving around and warming it up is going to do if the car already sees it's current level is the same as other tires.

BigEarl

also, thanks for bringing tire pressure levels to my attention. The tires don't look low at all. And Id think if levels were that low, the car should give warnings on all 4 tires.

mjeds

the TPMS doesn't care about the pressure in the tires. The system works by determining if there is a difference in the pressures between the 4 tires.

most systems work by determining if there is a difference via a preset percentage, depending on the manufacturer it can be between 10% and 25%, some systems also have a threshold so any tire that is below that threshold (i.e. 27psi) will pop the alert.

also keep in mind, you pressed the reset, so the system may be waiting for you to finish the reset procedure.. I believe the procedure is on page 492 of the RC manual.

Driving allows the system to actively scan and update. while sitting it might update over time, driving ensures that it is actively scanning and updating.

BigEarl

Exactly the type of answer I hoped someone would give. Thanks for taking the time to reply and thanks to everybody else that replied.

Merry Christmas!!

NemesisUK

Each time one adjusts the tyre pressures one has to press that button to rest the desired pressure the system expects as normal.

mjeds

per RC manual:

How to initialize the tire pressure warning system

Park the vehicle in a safe place and turn the engine switch off. Initialization cannot be performed while the vehicle is moving.
Adjust the tire inflation pressure to the specified cold tire inflation pressure level. (P. 614)
Make sure to adjust the tire pressure to the specified cold tire inflation pressure level. The tire pressure warning system will operate based on this pressure level.
Turn the engine switch to IGNITION ON mode. Press and hold the tire pressure warning reset switch until the tire pressure warning light blinks slowly 3 times.
Wait for a few minutes with the engine switch in IGNITION ON mode and then turn the engine switch off


Initializing the tire pressure warning system
■ The tire pressure warning system must be initialized in the following circumstances:
● When rotating the tires.
● When the tire inflation pressure is changed such as when changing traveling speed.
● When changing the tire size.

When the tire pressure warning system is initialized, the current tire inflation pressure is set as the benchmark pressure.


you do not have to reset when you add air, only when the above occurs.



BigEarl: As I stated above some systems have a threshold, looks like the RC uses that system but it is set by the owner/dealer. yours might be set @ the 27psi mark which is why the alert won't go away. you might want to get the tires up to the correct psi stamped on your door, then reset the system per the above so that you get the proper threshold/benchmark.

NemesisUK

From your own post...

"Initializing the tire pressure warning system
■ The tire pressure warning system must be initialized in the following circumstances:
● When rotating the tires.
● When the tire inflation pressure is changed such as when changing traveling speed.
● When changing the tire size."

As in, when one adds air?

mjeds

the reset procedure is to set the baseline/threshold. unless you are adding air or removing air because of a major shift in your driving habits, there is ZERO reason to change the baseline every time you add air.

My cold air pressure is 36psi, my baseline is 32psi, that means if any tire drops below 32psi I get an alert.. This is what I use 95% of the time.

This past August I made a major change to my driving habits, I drove cross country, nearly 6000 miles at highway speed in the dead of summer from CA to CO to TX, to TN, to GA and back. I changed my normal average traveling speed from 35mph to 75mph. Therefore a change in the baseline was required, as such I adjusted my tire pressure to 32psi and a baseline of 28psi. because at highway speeds in 100° plus temps when the roads are 160° or hotter; tires at 32psi cold will get to 42psi when they get hot. Having 36psi as a cold temp pushes the pressure to 45 - 46psi which is too high for the tires and results in poor handling and uneven wear.

when I returned I readjusted it back to where it belongs for my normal city driving. @ 36psi cold, my tires reach 40psi in my 30 mile commute to work when the outside temps are 80° - 90°. right now the temps are 60° - 75° and the tires settle around 38psi in that same commute.


and in case it isn't clear, to set a baseline you fill or deflate your tires to the desired baseline (in my case 32psi) then you run through the reset procedure. Then you fill your tires to your desired PSI (in my case 36psi). You don't want your baseline to be set at your cold PSI because then if the outside temp is lower than when you set the baseline and your tire pressure drops as a result of the cool air/ground you will get an false alert.

i.e. if you set the tires to 36psi when the car has been sitting for 4-6 hours and the outside daytime temp is 75°, the next morning when the outside temp is say 60° your tire pressure will have dropped to about 34psi, which will trigger the alert. Hence why I set my baseline @ 32psi.

Tire pressure drops about 1psi for every 10° of temp, (Fahrenheit). Where I live I can see a swing of over 30° in a given day, for example; it was 82° yesterday but got to a low of 47° last night. That is a 35° swing, and my 36psi set tires were at 33psi this morning. and by the time I got to work they were at 39psi, 31 miles @ an average of 40mph. I would see a low pressure alert every time I started the car if I set my baseline @ 36psi.

NemesisUK

That is a complete odds with what I have been told, read and practised over the last 40yrs of motoring. Tyre pressure are adjusted when the tyre is cold (that is at ambient temperature, having not been driven more than 1-2 miles) using slightly higher pressures if the car is more heavily laden or the average speed is higher, just as shown on the pressure label affixed to the car. Tyre pressures are derived from the axle weights the tyres have to support and the average speeds the vehicle are to be driven. Hence the manufacturer gives a range of pressures within which one is free to experiment to give the desired compromise between ride comfort, handling and wear. The only stipulation is to maintain the relative pressure differential between the front and rear so as to maintain the designed handling characteristics. Of course one can move outside those ranges but in normal road driving it's never usually required. One should always monitor tread wear across the tyre width and adjust the inflation pressure slightly to ensure even wear, reducing if the centre wears, increasing if the edges wear.

Regarding the tyre pressure monitoring system, my understanding is one adjusts the tyre pressures to the desired levels and then initialises the system to tell it what is the benchmark pressure. The system then alerts should the pressure deviate from that benchmark by a set percentage (approx 10-15% on my Mercedes, not sure what the limits are on the Lexus system).

mjeds

Lexus/Toyota uses a 2 step system.

1. if any tire drops below the baseline.
2. if any one tire has a 25% lower pressure than the others.

you will get an alert if any tire drops below your baseline, and you will get an alert if any one tire is 25% lower than the others even if it is above baseline.

as for the other stuff: Tire pressures fluctuate based on outside temps and the temperature of driving surface. 1psi for every 10° as a general rule. In places like where I live where the temps can fluctuate as much as 30° in a 24 hour period and as much as 60° between seasons, it is not uncommon to see a 5-6psi fluctuation in psi.

It is one of the factors as to why C.A.F.E. requires all dealerships to check and adjust tire pressures on all vehicles that come in for service, as part of our E.P.A. regulations, because people don't bother to check them on their own anymore.

http://www.tirerack.com/tires/tirete....jsp?techid=73