Tpms

[Stkid93]

My Tpms light came on today I checked all 4 tires. Back driver side was about 25/26 psi while the back passenger side was about 29.

my questions are:

1) at what pressure does our tpms light come on? The general rule of thumb I believe is 25% under the suggested pressure, so at 32 psi suggested that would mean the light comes on around 24 psi.

2) after refilling the tires how long do you have to drive before the light will go off? My last cars light went off almost Instantly but I’ve read that ford cheaped out on the system for the fiesta and it can take up to 20 minutes of driving to go off

3) is there a way to manually reset the light and turn it off? I tried using the accessport to clear the codes (which again worked on my old car) but it doesn’t appear to turn the light off with the fist. I also read some ridiculous thing about cycling the ignition and hitting the brake pedal and then cycling it again but that didn’t work for me. I read that procedure may require some sort of special reset tool or something?

also, any other information you have about the TPMS system on the fist would be appreciated. This is the first time I have gotten a low pressure light on my fist. And it seems pretty different from my Last car

 

[Capri to ST]

I'm not sure about the answers to your first two questions, I would also like to know what the threshold is for TPMS activation. I would guess it's about 8 lbs low. The only time mine came on, I turned out to have a slow leak in one tire and it was down to 20 lb. The system doesn't tell you which tire is low or what its pressure is, just that a tire is low.
Concerning resetting the light manually, there is a procedure in the owner's manual, but it's kind of cumbersome and annoying because it involves letting about half of the air out of the tire after putting it into a programming mode.
Because of that, I bought the Ford TPMS reset tool. I have seen it called a TPMS 19, and have also seen this part number for it-
8C2Z-1A203-A
It looks like this-

Here is a helpful thread from the forum on how to use the tool, the tool is required after performing the sequence of pushing the ignition button and pressing the brake pedal. You put the car into a programming mode by that sequence of pressing the start button and pushing on the brake pedal. When it goes into programming mode you get a honk to tell you that it's there. Then you walk around and point the tool at each tire valve and press the button, you then get a honk to confirm that that sensor has been reset.I used the tool after I got new tires the last time and it worked well.
https://www.fiestastforum.com/threads/ford-fiesta-st-tpms-sensor-training-motorcraft-tpms19.2293/

 

[Stkid93]

Update:

the original tire machine I used was broken, and it was letting a ton of air out as it was filling. So I managed to get the tire from 25/26 up to about 29 psi or so, thinking that would be high enough to reset the light, but it’s 20 degrees here and because it was broken it took forever to fill the tire and holding a metal piece for that long I ended up giving up.

However after driving around for a while the light was still on, so I decided to fill it above 32 psi, and bam the light went out instantly, didn’t even have to start driving. So here’s what I’ve learned

1) the light most likely comes on between 24-26 psi. And supposedly the tire has to be at that pressure for 10-20 minutes for it to actually come on. I don’t know if that’s true

2) once the light comes on, it will only go off once the pressure goes back above 32 psi. Putting it back above the 24/26 Psi threshold will not turn the light off. So when talking about the light coming on, and getting the light off, the pressure threshold is different

3) once the pressure gets above 32 psi the light should go off immediately. I’ve read you need to drive for 10 minutes or so, but that wasn’t my experience.

4) don’t want until the tpms light comes on to fill your tires. As the 24 psi threshold is pretty low and will drastically change the handling of your car. And can cause tire wear issues, etc. this one should go without saying, but I got lazy because of the cold and didn’t follow my own suggestion. So no matter how cold it is and how lazy you are. I suggest checking your tire pressures every month or so if your area is cold. Here In CT the weather was 60 and humid recently, and then today it was 16-20 degrees with the “real feel” between 5 and 9. That kind of temp drop can take 4-6 psi out of your tire. Which is probably what happened to me. The pressure probably slowly started to drop until it hit the 24-26 psi threshold. (Either that or I have a nail in that tire I didn’t see lol)

 

[Intuit]

When it gets dead-cold like this I recheck my pressures. (and wipe down my door seals with silicon spray lube) Had a brand new leaky Cooper brand tire and low 20s is what I routinely saw. If you're on stock 40 sidewall, that is frankly too low to avoid damaging the wheel here.

System is designed around battery conservation. So updates are infrequent. How quickly it does or doesn't go off I suspect may just be coincidence. Having to break down a tire just to replace a damn TPMS sensor, I can appreciate that. One question I would ask my fellow FiST-ers is, has anyone needed to replace a sensor yet? That said, I replaced mine but the sensors were actually good and it was the new Autel TPMS tool that was bad. They had a known defects but kept right on selling them because the defects take some time to show up. I'll never buy anything Autel again.

 

[Capri to ST]

One question I would ask my fellow FiST-ers is, has anyone needed to replace a sensor yet?

I'm not sure what the expected life of a TPMS sensor is, but I might replace mine next time I get tires since they'll be accessible then. That'll be about 2 years from now, and the sensors will be 10 years old.

 

[rallytaff]

I've only replaced my tpms sensors once in 9+ years. Not being technically minded, I occasionally got a warning light, normally on a fwy. I bought the tool about 2yrs ago and recently had to get rid of the light. If you go through the sequence with the brake correctly, it will work as I found out. I surprised myself!

 

[SteveS]

I had to replace the original sensors on our 2019 after only about 2 years. Neither the tool I have (shown above) nor the one at our Big O tire store could get them to respond.

 

[rallytaff]

I got the one off Amazon that will do Fords and GM cars. Works for me. It's in the car and I'll post something later on for the make etc.