TPMS Monitors

brian6pac said

Let me rephrase that, The TPMS monitor the tire pressure and if the pressure on the door says 36psi that is what the sensors are programed for, If the pressure veries up or down to much it will turn on the light. GM's are pretty tight tolerance IIRC
4-6 psi in ether direction will turn on the light.

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I think the industry standard is 10% of the reccomended pressure in the door jamb. So for 35 psi reccomended it will come on at or around 31.5 psi.

Other manufacturers may differ slightly from 10% value.

I dont think ive ever seen a tpms light come on for a gain in pressure, that wouldnt make much sense, the psi rating in the door jamb is supposed to be a cold pressure setting, meaning that the vehicle has been parked and not in direct sunlight for at least 4 hours. Pressure will go up a average of one psi per 10 degrees of temperature increase, so youd start out a 35 psi but at operating temperature the pressure may be as high as 40 psi, but yet the light shouldnt come on. There may be a few high end vehicles that expirience this maybe as to warn the driver the tires have gotten too warm as the pressure has increased, but most of your average trucks, cars and minivans wont expirience this