DTC B0021-2B: Left Curtain Deployment Control 1 - Signal cross coupled: Action

NOTE:

When the airbag connector is DISCONNECTED if the locking plunger can move to the locked position easily (reasonable pressure) the connector is damaged
Check for other cross couple DTCs set in the RCM, as that will indicate which wires are short circuit

Visually inspect the airbag connector(s), the locking plunger should be flush with the housing. If not, push the locking plunger in. Clear the Diagnostic Trouble Code(s) and retest
Refer to the electrical circuit diagrams and check the left side air curtain circuit for short circuit to another restraints circuit
If a wiring fault is detected, repair the wiring as required. Clear the Diagnostic Trouble Code(s) and retest