Sub-Zero Refrigerator Error Code 90 5 73

Error code 90 5 73 on a Sub-Zero refrigerator indicates an invalid log fault checksum. This is a firmware-level diagnostic fault related to the control board's internal data logging system. The checksum is a calculated value used to verify the integrity of data written to the board's non-volatile memory (EEPROM or flash storage). When the checksum computed at the time of a read does not match the value stored during the original write, the controller flags this mismatch as an invalid log fault checksum, signaling that stored fault log data may be corrupted or unreadable.

This type of error is most commonly caused by corruption in the control board's memory, which can result from power surges, voltage fluctuations, or an abrupt loss of power during a write cycle. If the refrigerator loses power while the control board is actively writing diagnostic or fault log data, the resulting incomplete write can produce a checksum mismatch on the next read attempt. Repeated power interruptions increase the likelihood of this occurring.

Because the fault is rooted in the control board's data integrity verification process rather than a specific mechanical or sensor-based failure, the refrigerator may otherwise continue operating normally. However, the error indicates the board may not be reliably logging or retrieving fault history, which can complicate future diagnostics. If the fault persists after a power reset, the main control board is the primary suspect and may require replacement to fully resolve the condition.