Conditions for Setting the DTC
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0826 sets when the transmission control module (TCM) detects an open condition in the TAP up/down shift switch circuit for greater than 6 seconds when driver shift request is commanded.