Conditions for Setting the DTC: P0816
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 a downshift request for 3 seconds when the transmission range selector is in D or 600 seconds in P, R, or N.