Conditions for Setting the DTC
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
DTC P1688 sets if unmanaged engine torque, gross, signal is less than 1.5 percent or greater than 98.5 percent for greater than a 2 seconds.