U1511, U1512
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The DTC will set when there is an open/high resistance in the local interconnect network bus circuit, or an open in the voltage or ground circuits of the motor or module.