Conditions for Setting the DTC: P0815
WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
The BCM detects an upshift request for 3 seconds when the transmission range selector is in D or 600 seconds in P, R, or N.