• Sign Up! To view all forums and unlock additional cool features

    Welcome to the #1 Fiesta ST Forum and Fiesta ST community dedicated to Fiesta ST owners and enthusiasts. Register for an account, it's free and it's easy, so don't hesitate to join the Fiesta ST Forum today!

TPMS how low before it triggers warning?

Messages
103
Likes
109
Location
Glendale
#1
According to everyone on here and the tire shop that rotated my tires this car has tpms. Yet I’ve had no proof that this system is active or does anything. I’m pretty sure my pressure has gotten as low as 26-28psi.

So my question is, how flat must a tire be before the warning light comes on? 20psi? 18psi?

When it does come on does it indicate what tire is low or is it just a single light?

I’m not one for the “stuff I hate” threads, but I gotta say the decision not to give a readout on the dash really has me scratching my head. You have a sensor, you have a signal, and Ford was just too lazy to program it into the display.

I searched. Maybe it’s in the manual..
 

koozy

2000 Post Club
Messages
2,815
Likes
1,386
Location
Los Angeles, CA, USA
#2
~10lbs. IIRC when I saw mine go off. Single light and car must be driven ~20 minutes with out of spec tire pressure before light is triggered.

If your tires have gotten to 26lbs without a light, it could be that when the TPMS sensors with setup the pressures were already lower than recommended and perhaps they just need to be reconfigured with the correct tire pressures in the tires.

I have the Ford TPMS tool, I can bring it to the next meet or when cruise through Glendale just let me know.
 
Last edited:
Messages
102
Likes
54
Location
Phoenix
#3
20 minutes being around 10psi below spec seems too long to be effective. I'd notice a -10 before getting out of my apartment complex(lots of speed humps), def notice after a couple turns of the steering wheel, which is why I'll prob forgo using TPMS when I get my next wheel/tire combo.
 
Last edited:

koozy

2000 Post Club
Messages
2,815
Likes
1,386
Location
Los Angeles, CA, USA
#4
In my case the sat car for 2 months. The TPMS are designed to go to sleep to save battery. It takes x amount of revolutions to wake them up, so time before the light comes on can vary. If they aren’t in battery saving sleep mode reaction to provide a warning would probably be faster. I based ~20 minute estimate from my own experience.
 
Last edited:
Messages
87
Likes
31
Location
The Sewers
#5
Yeah, I don't trust those sensors. When I had the steelies on over the winter without sensors, I would have to drive more than 10 miles continuously before the light would pop up on the dash. I always check the tires visually prior to driving away for that reason. I don't want to find out 10 miles later I have low pressure in my tire/s! :mad:
 
Messages
29
Likes
6
Location
Winter Park
#6
My Fiesta ST went nuts when I manually rotated my tires. It is set to different pressures front and rear. I had to do a reset procedure after my rotation to fix it.
 
OP
Booster
Messages
103
Likes
109
Location
Glendale
Thread Starter #8
To find the answer why not just drop the pressure and see?
Well this is how I got my answer but not exactly how I would have wanted. Leaving my gas station (ethanol) the other night I hit some newly installed steel plates doing about 50mph. It’s a dark section of road and these headlights suck, so BAM it happened. 1 mile later Tpms warning light came on. Visually inspected and the tires all looked okay but it’s not easy to see with a 40 series tire.

Checked with a gauge today and the right rear was 25psi so that would be a 30% pressure loss vs. oem air pressure.

These tires are totally smoked and I’m getting Indy 500s this week. I just hope that rim isn’t cracked, or maybe I hope it is cracked so I can justify rims.

Anyways, my next question on the subject — must I buy new sensors with new tires or can they be reused?
 


Top