Conditions for Setting the DTC: P0406
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
The EGR position sensor voltage is more than 94.7 percent of the 5-volt reference voltage or 4.735 volts for longer than 20 seconds.