Conditions For Clearing DTC

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.

A current DTC B21/31 will clear if a short to ground or open in the courtesy lamps supply voltage circuit is no longer detected by the BCM.
A current DTC B21/31 will clear if the open or short to ground in the battery positive voltage circuit to the BCM that feeds the courtesy lamps supply voltage circuit is no longer present.
A history DTC B21/31 will clear after 100 consecutive ignition cycles if condition for the malfunction is no longer present and no other BCM faults are detected.