Rule of thumb is one pound per ten degrees change...
Moon

 

the light comes on at 27 psi, cold weather will affect tire pressure. usaully the tire pressure light will go out once you reset the pressure back to 33psi (cold) and drive it around the block

 

I had the same problem, I took it to the dealer and they said I was missing a fuse, which was odd as I've had the car for a little over three weeks and have never touched the fuses. I would suggest looking at THE FUSE BLOCK. In another electrical mishap, my wife left the lights on and the battery went dead, when I jump started it in the morning the alarm went off and I could not turn it off. So i drove to the dealership horn honking and lights flashing. That is when they found that a fuse was missing, before then I thought it was normal to have the TPMS light on.

 

Manufacture specs say 24 to 26 psi; they are not very accurate devices, especially for the price they charge consumers tho the price to car makers are much less, just like tires.

 

Excellent. It's based on the PV/T equation where pressutre is absolute, meaning 30 psi is 44.5 psia and temprerature at 30 deg F is 560 absolute. Solving for a 10 degree change is pretty close to one psi difference.
Good number to know.

 

Rules of thumb are just that...happy to hear there is a sound basis for this one. Thanks.
Moon