Conditions for Setting the DTC: P0731
WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The TCM detects the calculated gear ratio with 1st gear commanded differs from the known 1st gear ratio for 2 seconds or longer.