Conditions for Setting the DTC: P1815
WARNING: This page is about a different car, the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The TCM detects D2 only, TFP manual valve position switch state during and after engine start for 3.25 seconds.