DTC B2193: Chain Of ECM-IMMU: Description
WARNING: This page is about a different car, the 2011 Nissan 370Z. However, it is still accessible from the selected car via links, so may be relevant.
BCM performs the ID verification with ECM that allows the engine to start. Start the engine if the ID is successfully verified. ECM prevents the engine from starting if the ID is not registered. BCM starts the communication with ECM if ignition switch is turned ON.