does it happen when you use the heater as well as when the heater's off? this also occurs in my aurion, therefore i have to use the air con to clear it, especially when its really cold. so i went through the owner's manual to find out that the button to use circulated air should be turned off to avoid that from happening, in other words, you need to use fresh air brought from outside to not have the windscreen and possibly the side windows fogging up. however, according to a thread on this site and personal experience, that is not advisable especially in poluted areas because the air con filter doesn't filter all the exhaust fumes from outside the car.