Anyone know the tolerance for the TPMS?

I checked my tire pressure this morning after a cold weekend and I was down to 25 psi. Since 32 psi is the recommended, I would have imagined that the TPMS would have lit up, but it did not.

So how low or how high does it have to be to trigger the system?

 

It's pretty inaccurate, I think it's around 18-20psi, you should definitely check your pressure occasionally because waiting for the pressure light to come on will probably be after some tread has been worn away unevenly. I think I had the light legitimately trip once in 6 years of ownership and that was on a cold day (It does reliably trip when you run wheels without tpms sensors).

 

I seem to recall they should trigger once the pressure is down by 25% of placard value (32 psi x 75% = 24 psi).

 

Thanks for the info, after surfing around I found a Popular Mechanics article that agrees with the 25% below standard. So I was still above this - although 25 psi is certainly not desirable so checking more often in cold weather is recommended. A good thing to know as I assumed that it would be less and that my car would let me know when I needed air. I'm glad I checked and will have to check more often.

 

IIRC, my TPMS on SUV trips below 26 PSI and every time it HAS tripped, it was the spare since it's tough to get to the stem and I don't keep it topped off like I do the 4 on the road. Of course, now that I'm in Florida, it never goes off like it did when I was in PA and Illinois.

Hopefully, you're aware that for every 10 degree F. drop/rise in temperature you'll have a corresponding drop/rise in pressure of roughly 1 PSI.