Diagnostic Aids

WARNING: This page is about a different car, the 2014 GMC Yukon XL 1500, 2014 GMC Yukon, 2014 Chevrolet Tahoe, and 2014 Chevrolet Suburban 1500. However, it is still accessible from the selected car via links, so may be relevant.

Motor control A shorting to motor control B could cause this DTC to set.
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.
EL-49741 harness is a good source for 9 V.
EL-49742 harness is a good source for B+ and ground.
The transfer case fill and drain plugs are a good source for ground.