TPMS
Cold PSI does not mean the coldest on that day, it's ambient temp, like not heated by fire, sun, high speeds, long trip, heavy load, etc. If the tire has been driven 45 miles at 127mph and the roadway is 112 degrees, the tire is not at ambient temperature. If it's between 70 and 90 degrees in the day but hits a low of 34 degrees at 2:00AM, the correct time for setting psi is in the day unless you drive a lot at 34 degree temps. A tire set at 34 degrees will have more psi-s when temps climb into the '90s.
I check / adjust as needed at start of seasons.
If adjusted in Summer, it's gonna be lower in winter.
If adjusted in winter, likely OK in summer as I use only good air and it can seep out through pores in rubber over time.
I run 40psi minimum in P275/55-R20s, but often will go 42.
My '07 has it's OEM sensors still, too, so far no lights except when a tire was low, but they've only been awake for 65,xxx or so miles.
Good battries I guess.
Anyway, my original battery was in the process of failing. The first time I saw the TPMS light was immediately after a slow crank and almost no-start. Coincidentally I spotted a metallic object on the front tire so I took the truck to my tire/general work shop. The little pin they found in the tire was barely stuck to it and did not puncture it. They tested the battery in every way and said it was good. However, I still was having weak cranking, and the TPMS would pop up. Finally I realized I have to replace that battery and I just put the new one in. 13 years on a battery is long enough
. The old one was 540CCA and I went ahead and sprung for an 840. Boy, does the starter spin now. And, no more TPMS. I'm not sure what the connection was but obviously severe low voltage can play hell with electronics.
It has happened to me over 1/2 dozen times, the first time I thought the a sensor was bad and had it replaced, it then happened several times after that and I started doing some research and found out that some devices can emit rf interference that will cause the system to go into TPMS Fault mode
Our Mustang is the same.
Her '19 Forester reports pressures though.
Apparently Dodge (er um Ram - IT'S A RAM!) of all manufacturers uses a system that knows which sensors are at each wheel, including automatically figuring it out when a tire rotation has occurred.
But both my '07 F150 XL, '08 F150 XLT and '11 F350 XL are just all or nothing - an error warning or light for ANY error ANYwhere. Not super helpful.
I'd be glad to never see TPMS again - I was raised learning to drive when a motor vehicle operator was expected to have other responsibilities like regular tire pressure checks, oil level checks and using side and rear view mirrors. Now we're just glad if a driver can go a couple blocks without having to have "collision avoidance" save them
You mention rotation. Odd, I rotated tires in about 2010 or 2011, no lights. Bought new tires this past November of 2019, marked my wheels for position, Discount Tire mounted them and still mixed them up, and then they had to reset the TPMs they said because it was causing a light?
I wondered why didn't I get a light when I rotated them that time some years ago?
I had also mounted and run some like new take offs from a '09 F150 in 2015, but I had hauled them to my buddy's shop and did them one at a time myself, so then they went back like they were put in that earlier rotation, so I would not have expected a light then in '15.
Ford Trucks for Ford Truck Enthusiasts
I don't know if the variance in F150 pressures front to rear is enough to be noticed by most owners in this situation.
The problem with Ford's system (and many others) is even though the vehicle may (or may not) KNOW which sensor is bad the dash isn't sophisticated enough to tell you, so you're left guessing and checking all 4 pressures. If all 4 pressures are good, you still don't know which sensor is then dead or defective without having the tool to "read" each sensor, physically at each wheel.
Furthermore, while some vehicles automatically know when tires have been rotated to different positions, most rely on the USER to recalibrate after a rotation. If this has not been done (and quite often it isn't), the vehicle may say "left front" is low when in fact that has since been moved to "left rear." In other words, garbage in, garbage out - it only knows as much as "we" have told it regarding position.
On the SuperDutys with a text DIC "taping over the light" simply isn't enough. You'll get a text message dead center of the dash each time you start, and again 25 miles into driving, accompanied each time by an audible chime. I'm wearing out that RESET button on my steering wheel LOL. Taping over the DIC is dumb 'cause it might someday tell me something else I'd want to know. FORSCAN can apparently remedy this, though.










