DTC B2191, P1615: Difference Of Key: Description
WARNING: This page is about a different car, the 2012 Nissan Xterra. However, it is still accessible from the selected car via links, so may be relevant.
Performs ID verification through BCM when key is inserted in key cylinder.
Prohibits the release of steering lock or start of engine when an unregistered ID of mechanical key is used.