TPMS light weirdness

So since it's getting cold tire pressures are dropping. This morning I came out to my truck and was greeted with that familiar yellow light. What I don't understand is WHY IS THE LIGHT ON? The FEDERALLY REQUIRED door jam sticker on my truck says the recommended tire pressure is 29PSI. Why is the light telling me that the tires are correct? Shouldn't it tell me when they are LOW? And why is 29 too low for 3 tires but not the 4th?

I normally run the tires at 32psi cold and inflating them back up isn't a problem. I'm just curious

 

I have been having this same problem usually with just one tire.

 

I’m nearly certain the system alerts you when there is a big change in pressure. So if you were running say 39 pounds then it dropped to 29, you lost 10 pounds so it’ll alert you.

 

Any idea what the TPMS pressure was set at for PSI? I'm in a 2nd gen and have a button where I can reset the PSI to whatever I want based on the current tire pressure, not sure how that works on a 3rd Gen.

I tried to find out what percentage below the light would come on, but can't find anything.

The three tires that are illuminated could be as low as 28.5 while the one that isn't illuminated could be as high as 29.4 (all round to 29). I'm betting the system sees the decimals, but the screen doesn't.

 

It all depends on where the system pressure was set last. Bring them up to around 32 cold and see if it clears.

Had an oil change done at Walmart on my 2nd gen a few years ago and they put the pressure down to the door sticker value and lit up my TPMS system. I was running after market tires at 36.

G.

 

And don't be surprised if the tires are mixed up vs the screen. I kept filling up one of the tires on my wife's car using the screen as the gauge... I started wondering if the screen had a big delay until I noticed a different tire than expected was now over inflated by 15 pounds

 

That happened to me a month ago, just add 2 psi each tire restart your truck and drive it a couple of blocks. It will reset and all is good

 

I don't know. Maybe try putting in the to see if it goes away.

 

I think a 10 percent drop is what triggers the light.

 

There is a reset button under the dash. If the button was pushed when the tire psi was high it could trigger the light to come on even though the psi is still okay. I can’t remember what the manual said the pressure drop was to trigger the light, 5 or 10 psi lower than when the light was reset and the light comes on

 

The TPMS learns what you normally keep your tire pressures at. It stores that info inside the tpms computer and sets a “threshold” accordingly.

If the TPMS system senses a significant tire pressure drop and hits the threshold # it will trigger the warning light.

I pulled the following info from Toyota’s FAQ site:

To reset the system, first make sure the tire pressures are correct.

Turn the engine on, then press and hold the reset button. Hold the button down until the TPMS indicator light in the instrument panel blinks slowly 3 three times.

Wait for several minutes with the engine running, to allow the system to record each tire's pressure, then turn the engine off.