Diagnostic Aids

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.

It is possible to have windings inside the motor shorted to the case resulting in a short to ground causing this DTC to set.
The default actions for C0321 may set C0306.
Harness EL-49741 is a good source for 9 V.
Harness EL-49742 is a good source for B+ and ground.
The transfer case fill and drain plugs are a good source for ground.