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.
The ECM detects that the commanded state of the MIL driver and the actual state of the MIL control circuit do not match for greater than 2 seconds.