Can anyone tell me what the alert threshold is for trailer TPMS? Should it alert if a tire is 1# below where you set the alert? Or is there some degree of tolerance?

I activated trailer TPMS on my '21 and am not getting an alert despite having set the alert level 5# above the tire pressure, and drove a long distance. The pressure increased during that drive, of course, but I believe it was below the set alert level.

 

I have an aftermarket set - they're really meant to alert you quickly to a catastrophic loss of air, not help you keep them exactly where you initially inflated them to. Basically if you have a tire drop 10psi or more you want to know ASAP either immediately after or before a catastrophic failure. I assume the Ford TPMS works the same way.

 

I know how they work. I used to have a TST TPMS and it worked well. I'm hoping I can get the Ford trailer TPMS working as well as it would if it were installed at the factory. I'm sure it's just a setting in the software but I don't know which.

 

As a late closure to this topic, I got the bright idea to configure the spare tire of the trailer as if it was on an axle. (I put a fifth sensor on the spare when I installed the system, to be used if I had a blowout.) I bled a little air from the spare to confirm the truck was tracking pressure changes. That worked. Then I removed the Schrader valve to simulate a blowout. I got an alarm! Yay!

I still don't know how bad it has to be before it alarms but assume it works as designed. If anybody knows how Ford's trailer TPMS functions on a Gen 14 F150, with respect to when it alarms relative to the trailer tire pressure setting, please share your wisdom.

 

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