ECU Malfunction
WARNING: This page is about a different car, the 2003 Saturn LW300, 2003 Saturn LW200, 2003 Saturn L300, and 2003 Saturn L200. However, it is still accessible from the selected car via links, so may be relevant.
The BCM performs an electrically erasable programmable read-only memory (EEPROM) checksum as a part of its internal diagnostics as the BCM is operating. When the EEPROM checksum does not equal a predetermined value, DTC B1000 - ECU Malfunction sets. The checksum is the contents of each memory location in EEPROM added together.