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TPMS how low before it triggers warning?

Messages
114
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122
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
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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.
 
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Messages
139
Likes
87
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.
 
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koozy

2000 Post Club
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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.
 
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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
114
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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?
 
Messages
139
Likes
87
Location
Phoenix
#10
I opted to go without sensors with my new wheel/tire setup. My light just came on today after ~100 miles of driving, including the back & forth to work 4 times.
 

Intuit

1000 Post Club
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Location
South West Ohio
#11
It's such a huge environmental waste, it seems they've done everything possible to maximize battery life for those sensors. So I've heard a mechanic say they'll last as much as ten years or, what is probably two tire sets for most people. Don't know if it's intentional or even unrelated, but it also seems to have the effect of absolutely minimizing false alarms as, even nearfield wireless technology can be intermittently unreliable. It's probably not uncommon, especially in bumper-to-bumper traffic for example, or noisy radio environments, for the sensor to miss a trigger, and/or the system to miss/understand a reply. Instead of sounding off the alarm over a missed trigger point, it's likely waiting for several missed triggers; and is why it takes 20 or 30 minutes for it to flag a low sensor or misread.

I've had a hellova time waking up the sensors after seasonal storage and have unnecessarily replaced a set. (mechanic got free sensors) I only discovered this after the next set pulled the same nonsense of taking two tanks of gas to wake up. Aiming for road craters seems to help them wake up faster. ;)
 
Messages
10
Likes
8
Location
Metro Detroit
#12
Had my TPMS warning go off last Thursday morning. Tire pressure on the Drivers rear was 23.5 psi. Based on that I would say the trigger point is 24 psi. A pressure that would be perfectly safe to drive on if you are using 16 inch rims but prone to wheel damage if you are using the stock 17's. BTW being an Old Fart and an Engineer I think that super low profile tires and wheels are just plain STUPID. The stock 17's are harsh riding and here in Michigan would need welding repairs darned near once a month. BTW, as an Engineer I will also state that IMO weld repairing a wheel is UNSAFE. Because welds will always have a heat effected zone that changes the metallurgy in that area and weakens the base metal used to make the repair.
 


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