Toyota Repair: 99 Sienna Tire Pressure Warning, air leaks, wheel speed

Question
At dealer's recommendation, replaced front tires. Since then, the tire pressure warning light comes on solid after driving for a few minutes. Reset button does not seem to do anything, have tried multiple methods. Took to dealer twice, they kept checking and adjusting tire pressures and hitting reset button (first time they thought it was fixed because light was out - they didn't know it has to be driven for a few minutes before it comes on). Now they agree there is a problem, but I don't have much confidence in them. Suggestions? Procedure to reset?

Answer
Are you sure all the tires are the same size, if so, maybe the other two tires that were not replaced need to be replaced also to make all tires the same.
The way the system works is that the computer actually doesn't read tire pressure but rather the rate of speed of each tire, this is based on the fact that as air leaks out of a tire it becomes smaller and so rotates at a different speed than the other tires, it is the difference in wheel speed of one tire compared to the rest of them that turns on the tire warning light, for some reason the onboard computer sees a difference in wheel speed from one or more tire, even a small difference in the diameter of the tires can turn the tire light on. Was this condition there before the tire replacement? If not I highly recommend replacing the other two tires with exactly the same brand and size.