Reference: 2006 Explorer XLT
Problem: "Low tire pressure" warning comes on when outside temp drops
below 50F degrees. Pressure in all tires check good (32 psi) when the
warning light is on or off. Warning light will stay on for 2-3 days
before resetting, even though the outside temp reaches the 60's. A
30+ minute drive at interstate speeds will also reset it.
It's damn aggrevating to have to reset the light every time I start
the engine, especially all winter long.Two trips to the dealer service
rep got nothing more than "mine does that too", or "they all do
that". Have any of you Explorer drivers had this problem? Know of any
service bulletin fixes?
You're right, the sticker does say 35 psi. Damn, after a lifetime of
32 psi, I never thought to look. But on the other hand, 32 is within
10% of 35 and "shouldn't" cause a problem. But I'll check at 35 psi
and see if it makes a difference.
Is the higher pressures due to larger tires (16" vs 15")?
Is 35 the pressure on the vehicle sticker (probably located on the
driver's door jam). The pressure chosen is related to a lot of
factors, vehicle weight, tire type, expected usage, fuel economy
concerns, safety, ride, handling, etc. There are industry standard
load vs. inflation pressure tables for all tires of a given size and
I would expect the tires on your truck have a maximum pressure of 44
psi. However, the maximum load they can carry is probably the same
from 35 psi to 44 psi (assuming they are 104S tires). The "extra" 9
psi allows for higher pressure recommendations for high speed driving,
or better performance. When P series tires are used on Light Trucks
and SUVs, the maximum load is derated (usually by 10%). So, when you
mount p series tires on a light truck or SUV, the maximum load rating
shown on the tires sidewall is higher than recommended by the tire
manufacturer. The tires on your truck are probably rated to carry 1804
lbs when used on an SUV (at any pressure from 35 psi up to the maximum
shown on the sidewall). The sidewall probably says the maximum load is
1985 lbs (if you reduce 1985 by 10%, you get 1804 lb)
There are load inflation tables for some tires available at
This is a Goodyear chart, but all tires of a given size and type are
the same. The load vs. inflation table for a P235/70R16 mounted on an
SUV is as follows:
PSI Load (lb.)
35 1804 (maximum load for load range 104S tires - which is what you
38 1864 (applies to load range X tires only)
41 1954 (applies to load range X tires only)
According to the owners manual, the light should come on if one of the
pressure in one of the road wheels drops 25% below the recommended pressure.
So, assuming the recommended pressure is 35 psi, the light should come on if
the pressure in one or more tires drops below 26 psi. I would be suspicious
of your pressure gauge if you are constantly having this problem.
Are you still using the OEM tires? Tires with steel belts in the sidewalls
are a no-no.
As for the "they all do that line." Pure BS. Find a good gauge and set the
pressure properly (cold - The tire pressure when the vehicle has been
stationary and out of direct sunlight for an hour or more and prior to the
vehicle being driven for 1 mile). If the light is on in the morning when you
get ready to go, check the pressure. If it is less than 25% below the
recommended pressure, take it to the dealer and tell them to fix it. Don't
let them BS you. If they start that, mention "safety problem." I searched
the NHTSA Recall, TSB, Defect Investigation, and Complaint databases. There
was exactly one entry (in all data bases combined) related to the 2006
Explorer tire pressure monitoring system and it was a weird one. Here it
Complaint Number: 10169074
2006 FORD EXPLORER LIMITED DRIVER SEAT WOULD NOT RETAIN MEMORY ON #2
SETTING. WHEN EXITING THE VEHICLE THE SEAT WONT GLIDE BACK UNTIL THE #2
BUTTON IS PUSHED. TIRE PRESSURE LIGHT ILLUMINATED. *KB THE DEALER HAD TO
REPROGRAM THE SEAT MEMORY MODULE AND REPROGRAM BOTH REMOTES. THE DEALER
RESET THE TIRE PRESSURE SENSORS. *NM
If it was true that they "all did that," there would be more than one weird
complaint in the complaint database. You can always add one if you like -
As I said, all 4 tires read the same pressure with very minor change
in psi between the warning light on or off. And I have used several
pressure guages with only minor variations between them. As a side
note, during the summer I picked up a nail and had a slow leak. The
warning light did come on when that tire got down to the mid 20's
pressure. Repaired the tire and the light went out. So that part of
the system works. This problem seems to be temp related rather than
Still using the OEM tires.
That's what I thought also, but wanted some input.
Except that temperature and pressure are directly related (Charles's Law). If
the pressure increases, so does the temperature. If the temperature increases,
so does the pressure... at least in a closed vessel.
"Mortimer Schnerd, RN" <mschnerdatcarolina.rr.com> wrote in message
True, but not by 25%.
In order for the pressure to drop by 25%, the temperature would have
to drop by 25% - and you have to use an absolute temperature scale.
70 degrees F = 529 degrees Rankine (an absolute temperature scale
using the same "size" degrees as Fahrenheit), so for the pressure in
the tire to drop 25%, the absolute temperature of the air in the tire
would have to drop by 25%, or 132 degrees F. So if the temperature
dropped from 70 degrees F to -62 degrees F overnight, you would expect
the tire pressure warning light to come on. I don' t think there is
any place on Earth with an overnight temperature swing of 132 degrees
F. Maybe the moon....
You're taking the use of the word "directly" literally, as if there were a 1:1
relationship. I'm using it as the opposite of "inversely". In an inverse
relationship, as one goes up, the other goes down. In a direct relationship, as
one goes up, so does the other.
IIRC, a scuba cylinder's internal pressure will raise or fall 4 psi for every
degree Farenheit's difference. That's not a 1:1 relationship but it is a direct
Given that a rubber tire is going to flex more than a steel or aluminum
cylinder, I would expect even less of a rise or fall of psi with temperature
change.... but it will rise or fall.
Sure it is. The temperature alone is enough to cause a burst disk to blow out
if you leave a tank in the trunk of a car baking in the sun. The burst disk is
designed to blow about 1000 psi over the working pressure of the tank. Normally
that would preclude such an event but the disk weakens with each cycle of the
cylinder... I.E., it flexes as you use and refill the tank. I have personally
witnessed a blowout of a burst disk in the trunk of a car sitting in the sun
down in Florida. Much noise, much fog (instant condensation of any moisture as
the tank pressure drops very rapidly), no damage (except to your drawers).
I don't think the disk would have let go on a cool day. The only other time
I've ever seen disks blow was during filling. Rapid flexion, rapid heating of
the cylinder as the pressure increases followed by rapid chilling of the valve
(it often will ice up) as the tank rapidly empties.
Whether we're talking about a scuba tank or a tire, it's a closed cylinder.
Both flex to an extent and both adhere to Charle's Law.
Assume you filled the tank to 3000 psi at 32 degree farenheit, and then let
it sit in the trunk of your car and drove to Florida, in the summer.
Generally you would expect the maximum temperature in a trunk of a car in
Florida in the summer to not exceed 140 degrees F. What would the prssure
T1 = 32 degrees F = 491.4 degrees R (Rankine, absolute temperature scale);
P1 = 3000 psi
T2 = 140 degrees F = 599.4 degrees R (Rankine)
P2 = 3000*599.4/491.4 = 3659 psi. (more or less)
Seems like the tanks needs to have fatique life established if the blow out
disks are failing at only 66% of the design point.
Tires flex all the time. Every rotation flexes the tire. But tires have a
very long fatique life (they'll fail from material deomposition before they
fail from flexure, assuming appropriate loads and proper inflation). I am
surprised scuba tanks seem so fragile.
This really has little to do with the pressure in the tire, or why the TPMS
was going off on cold mornings. As I said before, there is no way a properly
inflated tire is going to have the pressure decrease by 25% becasue of a
change in the temeprature overnight - at least on earth.
The annual visual / eddy current inspection of SCUBA tanks is supposed
to catch fatigue cracking. Tires and wheels which are subject to far
more severe service under highly variable conditions have no such
inspections. Both are life safety related too...
The tanks themselves aren't fragile. I've never personally witnessed a tank
fail in 10 years as a dive shop manager. But those burst disks are designed to
fail long before the tank does, much like a fuse should fail before the
protected component does. So the combination of numerous flex cycles combined
with sitting a tank in the sun can cause a premature failure of the disk....
Charle's Law in action.
I used to slow fill tanks sitting in a water bath inside my air conditioned
store.... say at 70 degrees. The idea was to provide an honest fill. Places
that just shot the air to the tank might initially read 3000 psi (which made the
tank HOT) but by the time you got to the dive site, the temperature inside the
tank will have equalized with the environment. You got into 70 degree spring
water and read your gauge, you might find you were 300 lbs light. So you either
overfill initially or you could fill slowly or you could do both. I did both.
Filling a tank to 3150 psi would yield a true 3000 psi at the dive site.... and
a damned sight more in the trunk of a hot car.
Better for a $2 burst disk to blow than a $150 tank.
Not by a long shot, they are damned beefy. I recently cut two AL80 tanks
that had failed inspection apart for my dive shop to use for display in
classes. One was cut lengthwise to give a nice overview half and the
other just the top section cut off to pass around to show hairline neck
fractures. I rough cut them with the plasma cutter which was pretty
impressive itself, blowing through up to about 3/4" thick aluminum, and
then threw the keeper pieces on the mill and milled the plasma cut
surfaces away leaving a nice finish. Given the current metals pricing, a
condemned SCUBA tank is still worth a few $ as scrap aluminum.
"Mortimer Schnerd, RN" <mschnerdatcarolina.rr.com> wrote in message
The amount the pressure changes is a function of the temeprature
change and the initial pressure. P1/T1 = P2/T2 for gasses that
approximate an ideal gas (air at normal pressure and temepratures is
not too bad, as long as it is dry).
Assume intial temperature (T1) of 70 degree Farenheit which is 529
degrees rankine and an inital pressure (P1) of 3000 psi. Assume P2
Pressure of 3004 psi. T2 would have to be:
T2 = T1*P2/P1 = 528*3000/3004 = 527, which is your 1 degree change
However, if the pressure is only 1000 pounds, a 4 psi change would
require around a 2 degree temperature change.
T2 = 528*1000/1004 = 526, which is a 2 degree temperature change.
I am not disputing that, but there is no way the pressure in the tire
will rise or fall enough to affect the operation of the tire pressure
monitoring system over a normal temperature range, if the tire is
properly inflated (inflated cold to the vehicle manufacturers
Tires change volume (but not necessarily shape) very little over the
range of normal inflation pressures. The tire carcass is not as rigid
as a scuba tank, but it is not a balloon either. The shape of the
cross section changes, but the interior volume is relatively constant
unless the pressure in the tire is very low, or the tire is
drastically overloaded (well beyond any normal load). The change in
volume is trivial and can be ignored for a change as little as 25%
below the recommended pressure.
" I searched the NHTSA Recall, TSB, Defect Investigation, and
There was exactly one entry (in all data bases combined)"
at http://autosmash.com under the TSB section for Exploreres you'll
"TIRES:PRESSURE MONITORING AND REGULATING SYSTEMS
SOME OF THE VEHICLES WERE BUILT WITH INSTRUMENT CLUSTERS THAT WERE NOT
CONFIGURED PROPERLY FOR USE WITH A REVISED TPMS MODULE. THE TIRE
PRESSURE MODULE SYSTEM (TPMS) IS FULLY FUNCTIONAL, BUT THERE IS NO
VISUAL INDICATION TO A DRIVER IF THE ..."
I increased the pressure in all 4 tires from 32 psi to 35 psi.
Last night the temp dropped down to 32F degrees.
The "low tire pressure" warning did NOT come on.
Based on previous responses, I have no idea why the increase in
pressure would solve the problem, but apparently it did. Maybe the
sensor is operating with some effing Ford algorithm or something.
Anyway, just advised all of the solution in case anyone google
searches the problem in the future.
Thanks to all who responded.
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