Testing the Tire Pressure Monitor System?
 

Does anyone know the specs for when TPMS will light up for low tire pressure? The other day I was showing my Son (and other Cubscouts) how to check tire pressure and how to fill up tires, so I purposely bled one tire down to about 22psi to see what the boys would do. Sure enough they found it was low, but before refilling, I took the truck out for about a 1.5 mile drive to see if the tire pressure monitor light would come on. Most the time I was driving <25 MPH, but I did get up to about 50MPH for a block or so. Nothing happened with the TPMS so I don't know if I let enough air out, or if it has to be low for a certain distance or speed before indicating low. Perhaps someone with the Factory Service Manual (or DVD's) can see how this is supposed to function.
BTW, we did fill the tire back up to the proper pressure.:p

I would think that 22 psi would be low enough to activate the sensor. May be taking it on the road heated the tire and raised the pressure some. But seeing that some here have had problems with their 07 pressure sensors may be there is a problem.

I my Nissans the TPMS blows your ears out at 28 PSI. The warning sound will make you jump. I would think the PSI would be the same for most auto maker but I guess I'm wrong. You don't think you have a faulty senor/senors do you?

I just wanted to test the system. I have no reason to believe that it doesn't work, but I'd like to understand how low the tires need to be before it warns. My TPS light comes on when I start up, and then goes off. Its never turned on other then that.

Generally speaking I am very unimpressed with the TPMS on this truck. I've had issues with it the other way where you are driving along and it starts warning you of a problem when none exists. My opinion based on my experience with this vehicle is the system needs a lot of work. On my Honda it has never given me a problem.

the TPMS went off for the first time on my 07 Mustang today. 3 tires where at 32psi and the LF tire was 28psi. I would assume that all Ford monitors would be the same.
My Expy has never set the monitor off, but I check the tires periodically and they are holding steady.

my 03 expy was saying check spare tire pressure the other day. i did, and found it to be at 20 psi. when i bought the truck, the warning was on as well, and if i remember correctly, it was around 20 as well(over a year ago though, so could be wrong).

How do these systems work? Is there a battery in the sending unit attached to the rim?

there is an antenna built onto each valve stem that send the signal to the tpms processor.

they look like this aftermarket kit: https://www.ford-trucks.com/forums/6...ng-system.html

But our expeditions are not in the valve stem, the unit is strapped to the rim with a belt or such.

ah, i didnt know that. i know the 03-06 are the valve stem style.

Not to thread jack, but I recently had my tires/rims replaced and they transferred the sensors over, but unfortunately broke one of them. They replaced it, but they did not register the new sensor. Does anyone have the maintenance manual that tells how to register a new sensor? I know Chevy does a key cycle to enter the program mode, don't know about Ford.

dealer has to program the sensor to the module

You are right, just came back from the dealership, they want 98.00 or one hour's labor to reprogram it to see the new sensor. Looks like I will make the 25 mile drive back to the 4WD shop to have them do it on their account. Hate driving all that way, but I will save 80 bucks or so. :mad:

If they broke it they should fix it and it sounds like they will. Too bad you have to drive that far to get it done.