P2120, P2122, P2123, P2125, P2127, P2128

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 system voltage is more than 5.23 volts.
The ignition is in the Unlock/Accessory or Run position.
DTC P0641 and P0651 are not set.
DTC P2120, P2122, P2123, P2125, P2127, P2128 run continuously when the above conditions are met.