TPMS trigger

ExSRT8Guy · May 15, 2017

Searched, no luck.

At what pressure should I see a TPMS warning light? Found a nail in one tire, pressure at 22 psi... and no light!

It's an '08, if that makes a difference.

AndrewNagle · May 15, 2017

ExSRT8Guy said:
Searched, no luck.

At what pressure should I see a TPMS warning light? Found a nail in one tire, pressure at 22 psi... and no light!

It's an '08, if that makes a difference.

If I am correct the TPMS system is suppose to compare the 4 tire pressures and when one is lower than the others it tells you

I have had it trigger when 3 tires are at 30 psi on one at 28psi

Not sure this helps
Andrwe

46addict · May 15, 2017

I have my rears at 28 and fronts at 32 and that triggered the light.

edit: I lowered the fronts to 30 and drove it twenty miles to work and the light is still on.

07 Boss · May 15, 2017

Well that's weird. I run my fronts at like 38-40 and the rears at 28. I've run them as high as 45 at the track. 15 psi difference and no warning or light. I know if my rears drop below 27 I get a sensor warning, but i don;t think it has much to do with tire difference.

ExSRT8Guy · May 16, 2017

Well, looks like I'm going to have to dig deeper. I don't think the system compares pressure in the four tires; I think it looks at each individually.

In the Explorer, the light comes on if pressure drops below 28.

Gabe · May 17, 2017

My light was on for the last few days, rear tires are at 27.5 cold, fronts at 32.
Today it got into the 80's, we reached 90 degrees for a few hours, light has been off most of the day, I'm assuming because the heat made the temps go up a little.

I've run the rears at 28 psi with no light but as soon as one goes to 27.5 the light would come on.

I don't think there's a factory setting, I think it has to do with whatever pressure the sensors were last trained to.

Do you have a TPMS sensor learn tool? They're about $40 from Tire Rack.

stkjock · May 17, 2017

Gabe said:
My light was on for the last few days, rear tires are at 27.5 cold, fronts at 32.
Today it got into the 80's, we reached 90 degrees for a few hours, light has been off most of the day, I'm assuming because the heat made the temps go up a little.

ummm... ya think.... :lol:

Gabe · May 17, 2017

stkjock said:
ummm... ya think....

Yeah, I've been known to think.
It's usually accompanied by grinding noises and smoke emanating from the top of my head

stkjock · May 17, 2017

Well, then the heat made the pressure go up......

RocketcarX · May 17, 2017

I remember reading they come on at 26 PSI, not because of a differential, def not a 2 PSI differential.

ExSRT8Guy · May 18, 2017

Gabe said:
Yeah, I've been known to think.
It's usually accompanied by grinding noises and smoke emanating from the top of my head

Ha!

No, don't have a scan tool, but could be time to invest. I assumed that once sensors were trained, it was for whatever pressure level they were calibrated to at the factory.

redfirepearlgt · May 18, 2017

The standard that became required in 2008 requires a low pressure indication when the tire pressure drops more than 25% below the car makers specified tire pressure requirements. This all goes back to the Explorer issue back in the early turn of the century. It is not a compare as I have also ran different tire pressures front to rear as well and have had no issues. Take the spec on the inside drivers door and multiply it by 75% and that will tell you the minimum pressure you should receive an alarm at. There is nothing stopping a car maker from setting this value tighter to any value less than 25%, but minimum by law is 25% of the manufacturers recommended pressure rating. Therefore is tire pressure is 36psi recommendation 27psi is the minimum pressure before the TPMS system will trigger an alert.....again assuming Ford is not running a tighter than minimum govt standard, which I doubt they are.

Gabe · May 18, 2017

The TPMS sensor remote is $31.45 on Amazon with free shipping:

Amazon.com: Motorcraft TPMS19 Remote Tire Pressure Sensor: Automotive

46addict · May 18, 2017

redfirepearlgt said:
The standard that became required in 2008 requires a low pressure indication when the tire pressure drops more than 25% below the car makers specified tire pressure requirements.

25% sounds about right. On my 08 GT the light triggered at around 24psi which is 8# below the door tag recommendation. My 07 has a new sensor on one wheel and it was programmed by Discount Tire. This car trips the light at 28psi as I found out. I've read third party tire shops can adjust the warning threshold.

redfirepearlgt · May 18, 2017

46addict said:
25% sounds about right. On my 08 GT the light triggered at around 24psi which is 8# below the door tag recommendation. My 07 has a new sensor on one wheel and it was programmed by Discount Tire. This car trips the light at 28psi as I found out. I've read third party tire shops can adjust the warning threshold.

Here is the document I referenced. I was curious to see if it was a standard or could vary from maker to maker of US cars. Further I was thinking 27psi was the magic number because it was the trip point on several cars I have had. But in researching I found its actually a percentage set forth by the National Highway Safety Traffic Administration.

https://www.nhtsa.gov/sites/nhtsa.dot.gov/files/fmvss/TPMSfinalrule.pdf

ExSRT8Guy · May 19, 2017

redfirepearlgt said:
The standard that became required in 2008 requires a low pressure indication when the tire pressure drops more than 25% below the car makers specified tire pressure requirements. This all goes back to the Explorer issue back in the early turn of the century. It is not a compare as I have also ran different tire pressures front to rear as well and have had no issues. Take the spec on the inside drivers door and multiply it by 75% and that will tell you the minimum pressure you should receive an alarm at. There is nothing stopping a car maker from setting this value tighter to any value less than 25%, but minimum by law is 25% of the manufacturers recommended pressure rating. Therefore is tire pressure is 36psi recommendation 27psi is the minimum pressure before the TPMS system will trigger an alert.....again assuming Ford is not running a tighter than minimum govt standard, which I doubt they are.

Perfect. Exactly the info I was looking for. Thanks!

Gabe said:
The TPMS sensor remote is $31.45 on Amazon with free shipping:

Amazon.com: Motorcraft TPMS19 Remote Tire Pressure Sensor: Automotive

I'm on it. Thanks for the link!

TPMS trigger

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