Can someone explain to me (in 50 words or less) the mechanics of the tire pressure monitoring system? My Lariat tells me on the dash the pressure of each tire, but how does it "know"??? Is the perimeter of the tire different at different pressures and is it counting the revolutions per second, or is there a laser somewhere measuring something else somehow? Just wonderin.

 

The basic system has a monitor inside each wheel that reads the tire pressure and wirelessly transmits it to the vechicle's computer. There are other systems, but you can Wiki and Google image yourself to death on those...

 

The sensor in the wheel reads the air pressure within the tire.

 

When you start up in the morning, the pressure readings will be off because the sensors have gone to sleep to save battery life.

After about 30 seconds of rotation, the sensors wake up. Your tires will also be different pressures if one side is in the sun.

Drive about 3 miles to get a more accurate reading.

You'll find that if you set your tire pressure in the morning at the coldest time of day, the pressure may be off by 1 psi after the sensors wake up and depending on the accuracy of your guage, and start to transmitt. No biggie. As you drive more miles and the tires heat up the pressure will increase. I usually see at least 3 to 4 psi increase around town. Do not release air to get the pressure back down. The pressure will go down as the tires cool off.

Most sensors will give you a Tpms light at a decrease of 10 to 15 psi. Depending on required air pressure.

 

Aren't the sensors built into the valve stems? I also presume they have a serial number or something such that they can be distinguished from one another.

 

Yes, each will broadcast a unique ID in it's transmission to the computer. That's why you have to tell the system to "relearn" after a rotation.

I really hope Ford has some good encryption on this connection...

 

what exactly do you have to do after a rotation to relearn???

 

It's in the owner's manual in the TPMS section under system reset.

I did it a while ago and it involves turning the hazard flashers on and off 3 times in 10 sec, then letting some air out of the tires one at a time in the specified order until the horn beeps. There are more details I don't remember, but the process was easy and only took a few minutes.

 

Performing the System Reset Procedure
Read the entire procedure before
attempting.
1. Drive the vehicle above 20 mph (32
km/h) for at least two minutes, then
park in a safe location where you can
easily get to all four tires and have
access to an air pump.
2. Place the ignition in the off position and
keep the key in the ignition.
3. Cycle the ignition to the on position
with the engine off.
4. Turn the hazard flashers on then off
three times. You must accomplish this
within 10 seconds. If the reset mode
has been entered successfully, the horn
will sound once, the system indicator
will flash and a message is shown in
the information display. If this does not
occur, please try again starting at Step
2. If after repeated attempts to enter
the reset mode, the horn does not
sound, the system indicator does not
flash and no message is shown in the
information display, seek service from
your authorized dealer.
5. Train the tire pressure monitoring
system sensors in the tires using the
following system reset sequence
starting with the left front tire in the
following clockwise order: Left front
(driver's side front tire), Right front
(passenger's side front tire), Right rear
(passenger's side rear tire), Left rear
(driver's side rear tire)
6. Remove the valve cap from the valve
stem on the left front tire. Decrease the
air pressure until the horn sounds.
Note: The single horn chirp confirms
that the sensor identification code has
been learned by the module for this
position. If a double horn is heard, the
reset procedure was unsuccessful, and
you must repeat it.
7. Remove the valve cap from the valve
stem on the right front tire. Decrease
the air pressure until the horn sounds.
8. Remove the valve cap from the valve
stem on the right rear tire. Decrease the
air pressure until the horn sounds.
9. Remove the valve cap from the valve
stem on the left rear tire. Decrease the
air pressure until the horn sounds.
Training is complete after the horn
sounds for the last tire trained (driver's
side rear tire), the system indicator
stops flashing, and a message is shown
in the information display.
10. Turn the ignition off. If two short horn
beeps are heard, the reset procedure
was unsuccessful and you must
repeat it. If after repeating the
procedure and two short beeps are
heard when the ignition is turned to
off, seek assistance from your
authorized dealer.

 

thanks but I wouldn't have the time, patience or access to an air compressor to do all this.

If it ever *** up, let the dealer fix it under warranty I guess. But I still don't understand how these things in the tires "send wirelessly" to the computer. To transmit a broadcast, wouldn't they have to have a power source, maybe batteries? How long do they last and do they need replacing or recharging? There's no power supply to the inside of a wheel---or is there?

 

Each Sensor uses a battery that last along time. It only transmitts when the vehicle is moving. So they last along time. Most last years. If your dealer does your oil changes and tire rotations, the reset will be done when the tires are rotated.

 

When you buy new tires, the shop will ask if you want to replace the sensors. It might be possible to just replace the batteries, but I think it's a one-piece design that they just toss and install a new one. But they do last a long time.

 

Dealer tells me the sensors cost about $80.00 each so well over $300.00 for a set. Their life expectancy will be a factor in how long I keep the truck. Does anyone really KNOW how log they last?

 

We offer programmed sensors for $160 a set or $40 each (typically sold with new wheels or a wheel/tire package). They say 6-9 years of service life, range is due to use of vehicle. Even sitting a battery will lose its juice.
For new tires it is possible depending on age of vehicle to just replace the valve stem portion of the sensor to save some cash.
For the OP there are systems that do not have a sensor in the wheel. They use the ABS system to read wheel speed. If all tires match then you are good. If one slows down or speeds up then the air pressure is off. The extra air or lack of will change the overall diameter of the tire.

 

I've been reading all these posts about the tire sensors on this forum and another forum. I put new wheels and some take off tires along with new Ford sensors (bought from Fairway Ford in Ohio) on my truck. Sensors were about $110 for all four. I wanted to leave my original wheels/tires complete so they could easily be put back on at anytime. I mounted the tires on my truck myself and did absolutely nothing to reset my system. Everything works fine. When I originally set tire pressures LF was showing higher so I let air out of that tire and it reflected that adjustment on the screen. Also, they must be reading the correct positions because as someone else stated earlier, the side sitting in the sun shows higher pressures than the other side until driven a little ways. I don't know how all this works but it does and IMO some are over thinking the whole process. BTW my truck is a 2016 F150 XLT Screw 157wb. Not that it makes any difference.