Tire Pressure Sensor

what is the limit on the TPS to get a warning light ON ?
I have a 2008 GMC Sierra with TPSM system.I had a PROBLEM with the warning light staying ON all the time . Gm dealer said they resetted the system .
Now my ECU is saying that the tire pressure is 30 PSI and it call's for 35 PSI normally, but the warning light did not come ON yet.
What is the limit before the warning light come's ON ?
Thanks Andre

The FMVSS requires the light to illluminate within 20 minutes of when a tire is 25% or more below the cold tire inflation. In your case this would be around 8 lbs. Manufacturers are allowed to turn on the light sooner and tighten up the pressure tolerance. I would expect your light to illuminate around 28 psi.

Thank you. I appreciated the fast response.

Andre