My 2007 F-150 has a simple TPMS that just shows the warning for a low tire. Except now it stays on and there is no low tire.
WAIT! As I am typing this I remembered the spare! Its been years since I checked the pressure in it! I was going to ask if the system shows the light when a TPMS battery goes down.

 

Is the spare hooked up to the TPMS? Cuz that would be weird. You'd have to disconnect it just to drop the spare.

 

TPMS is a wireless signal.

I don't think Ford intended the spare to be worked into the rotation on any of their trucks - AFAIK even alloy equipped vehicles get a black (or maybe silver) steelie for a spare. So I'd guess the spare doesn't get a TPMS sensor

Most sensors "sleep" and then "wake" with rotational movement, so putting one in an idle spare wouldn't do any good anyway.

I think OP has a failed sensor in one of his four driving wheels. Our wonderful gubermint protecting us. Gosh golly I sure am gr8ful dem smart fokes can watch out fer me (and mandate expensive sensors)

 

On steady = tire pressure
Blinking = Fault with system/sensor

To my knowledge Ford doesn’t use sensors in their spares, but that doesn’t mean a PO couldn’t have added one, although I’m not sure how they’d get it programmed correctly.

What pressure are you setting them to? Because temp affects pressure, tires that don’t seem to have leaks can fall below the threshold this time of year. Set all tires to the same pressure when cold (best done after sitting overnight when the tire temps have stabilized) and set them at least 4 PSI above the recommended pressure on the door jamb sticker (sometimes also found in the gas door) to compensate for the cold.

Do you do your own tire rotations? Because the sensor positions need to be relearned after each rotation even if it doesn’t tell you which tire is low.

 

Sensors have been known to fail... If you have all 4 tires above the pressure listed, and still have the light... Have the sensors checked.

 

My truck came with a regular wheel/tire spare. I'm pretty sure it has TPMS.
I'm also fully aware of adjusting tire pressures for cold contraction as well as hot expansion in warmer weather. You DO NOT add pressure above the recommendation when checking cold because the recommendation IS the cold pressure! It gets set the same, summer and winter. 'Cold' doesn't necessarily mean frigid, it simply means the tire temps after not being driven in at least an hour and preferably overnight. In my case it is 38 psi.
Yes, if it turns out to be not a spare tire issue, I'll have to get the individual sensors replaced as needed. After 13 years of having the truck at this same location and not having any TPMS problem, most likely its going to be failing batteries in the sensors.

 

im not sure the spare tires came with a sensor... WHY would they ?

 

Technically, with five wheels all the same, no temporary spare, you would rotate the spare in and out with the tire rotation. That way you would actually get the benefit of using the tire which would spread the tire wear out some. Obviously with the regular spare, since it would be used, it would have the sensor.

 

Most trucks have aluminum rims and a steel spare with a full size tire. Some trucks have steel rims and the spare MIGHT match the truck, but normally just a bare black rim... Rotating the spare is something we use to do in 1960. Don't see anyone doing that these days........ cars have temporary donut type tires.

 

Spare tire shouldn't have a sensor as they didn't ship with one. The tpms sensors also need rotation to turn them on for the reading. The sensors also have a 12 year average life.

 

The Tire Pressure Monitoring system (TPMS) on the 2007 & 2008 Ford F150 is similar to that used on many other late model Ford models. The TPMS system has pressure sensors inside each tire. The sensors are mounted in the drop center area of the wheel and are located 180 degrees opposite the valve stem. The sensors are held in place with a steel band that wraps around the inside of the wheel. The sensors generate a radio frequency signal every 60 seconds when the vehicle is traveling faster than 20 mph. The sensors do not transmit a signal if the vehicle is not moving, and they go into "sleep mode" when the vehicle is stopped for 30 minutes or more to conserve battery life.

 

The only way to know for sure about the spare is to check it. Sometimes the valve stem is a clue - I don’t know what Ford is using for stems on their newer trucks, but if the stem on the spare is different than the stems on the other wheels, it either doesn’t have a sensor, the stem was replaced with a generic type and the sensor was switched over, or both were replaced. Otherwise, any shop should be able to scan the tire with a sensor tester to determine if it has one.

As for pressures - the point of increasing the pressure above the recommendation is to simply check whether or not your pressure gauge and the sensor are reading close to one another. Your gauge may read 38 but the sensor might read it as 36 - if you set the pressure to 40, the sensor reads 38, and so on. I recommended going 4 psi over to account for the possibility of your pressure gauge being off as well as compensating for the cold of the season to make sure they were above the threshold.

I suppose I should have explained that in my first post; but I also never said increase the tire pressures and leave it that way until the end of all time.

I’m curious though - why are you so insistent that pressure isn’t set above the recommendation (when cold, of course)? I’d wager the fine print on the sidewalls of your truck tires states the max pressure to be well above 38 PSI - most light truck tires are rated to 80 at least.

 

I was wrong about one thing - the wheel is not the same as the others but the tire is the same size. Obviously it was not intended to be rotated with the others. It was down to 20 psi and I had fun figuring out how to assemble the operating rod to get it down - there were instructions in the jack stowage. So, the TPMS light did not come on when I drove it yesterday - it was a little warmer than it had been, or today when I drove it after working on the spare, when it was nearly 60. The other four tires were at 39 to 40 psi - I'll check them in the morning for the cold pressure but obviously they have no leaks.
So, if I keep getting the light, I guess I'll have to get new sensors.

 

'As for pressures - the point of increasing the pressure above the recommendation is to simply check whether or not your pressure gauge and the sensor are reading close to one another. Your gauge may read 38 but the sensor might read it as 36 - if you set the pressure to 40, the sensor reads 38, and so on. I recommended going 4 psi over to account for the possibility of your pressure gauge being off as well as compensating for the cold of the season to make sure they were above the threshold.'

Wouldn't have helped me on this truck even if I understood what you meant because its a base model without separate tire pressures - its just the light or no light. However on my one vehicle that does have this feature, I have noted about a 1 psi difference from my gauges which basically proves to me that my gauges are close enough for rock 'n roll!

 

TPMS sensors have batteries. The batteries don't last forever. You can't change the battery. Tire comes off the wheel. TPMS sensor is replaced. Tire needs to mounted and balanced. TPMS needs to be retrained.

On my 07, I have the type of sensors that are banded on the wheel. Every time the tires rotated, the light did not activate. Which indicates to me, that the sensors are not trained for the wheel position and do not need to be "relearned". I think that the older TPMS system did not "read" the position of each tire sensor. You can find the sensors online for a lower cost. Problem is that most shops will BS you about how they can't install your sensors, and insist that you buy their sensors for a lot more money. I get it. That's how they make a buck.

Your truck is over 10 years old. If the sensor batteries are dead, it would not surprise me.