DTC B1556: PZM EEPROM Write Error: Description
WARNING: This page is about a different car, the 1998 Cadillac Eldorado and 1998 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
DTC B1556 testing is run for each write or block of writes to Electronically Erasable Programmable Read Only Memory (EEPROM). PZM writes to EEPROM cell and then reads data back. DTC B1556 will set when data read by PZM does not match data written to EEPROM after 2 consecutive attempts. DTC B1556 will clear when data read by PZM matches data written to EEPROM.