Conditions for Setting the DTC: P0638

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 ECM detects that the commanded duty cycle for the range test high is greater than 80 percent for greater than 0.6 second.
OR
The ECM detects that the commanded duty cycle for the range test low is greater than 80 percent for greater than 5 seconds.