I tested when the low tire warning goes off today. I didn't have to drive it, because I noticed as soon as I let out a few psi of air while sitting in the driveway the DIC updated with the current pressure.
So, yesterday I set the TPM system to a P-Metric Standard tire type (I'm running stock type Bridgestone Dueler H/L Alenza) and set the pressure to 36psi on the next screen for both front and rear tires. I want the warning to come on earlier, before the tire only has 20-22psi in it.
I wasn't sure if the psi setting on the Tech2 screen was wanting the MAX pressure from the sidewall of the tire (44psi), the recommended inflation from the door jam sticker (32psi), or what you want the low warning to be. James above said that he thought the warning came on 10psi below the set psi, which should be what you keep them inflated to.
I have the tires inflated to 33psi cold. I started letting air out a couple psi at a time and looked at the DIC. The warning came on when the tire got just below 26psi.