DTC B1558, BCM EEPROM Checksum Error
WARNING: This page is about a different car, the 1997 Cadillac Catera. However, it is still accessible from the selected car via links, so may be relevant.
When ignition switch is turned to RUN position, BCM adds the checksum of EEPROM block. DTC B1558 will set when running checksum does not match computed checksum. DTC B1558 will clear when conditions for fault no longer exist or when scan tool is used. If DTC B1558 is set, clear DTCs and cycle ignition. If DTC B1558 sets, replace BCM.