[quote=johnkirkpatrick]Our tire pressure light comes on after ~30 minutes of driving.
We just got a new Sienna and do not have this problem. Our salesman said the tire "pressure sensor" actually measures a distance, not a pressure. It was something like the distance from the body of the car to the tire or maybe from the body to the road, can't remember. It learns the correct distance when you hit the reset and drive. It would be useful to know where the sensors are located and what they actually measure. I am thinking an ultrasonic radar, perhaps. A loose sensor would certainly cause problems. Ditto for loose wire. Badly aimed sensor.