Conditions for Setting the DTC: P0405
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 is less than 4 percent of the 5-volt reference or 0.25 volts for longer than 55 seconds.