DTC B1556, PZM EEPROM Write Error
WARNING: This page is about a different car, the 1997 Cadillac Seville, 1997 Cadillac Eldorado, and 1997 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 block of writes to 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. If DTC B1556 is set, clear DTCs and cycle ignition. If DTC B1556 sets, replace PZM.