Sub-Zero Refrigerator Error Code 55

Error code 55 means the zone thermistor in the indicated cooling zone has shorted. The thermistor is a temperature sensor that the control board relies on to regulate cooling. A short causes the board to receive an invalid signal, triggering this fault code. The refrigerator may not cool correctly in the affected zone until the issue is resolved.

Turning the unit off at the master power switch for 10 seconds and then back on will clear the error mode, but this does not fix the underlying problem. If the thermistor is still shorted after the reset, the error code will return. The wiring or thermistor must be repaired or replaced before a reset will hold.

Repair costs vary depending on whether the fault is in the wiring, the thermistor, or the control board. A thermistor replacement is typically the least expensive scenario, with parts and labor often ranging from around $150 to $350. Wiring repairs and control board replacements will generally cost more, potentially ranging from $300 to $700 or higher depending on the extent of the damage and local labor rates.

Some aspects of this repair are DIY-accessible, such as inspecting the wiring harness, checking connectors for corrosion or loose seating, and reseating connections. Replacing the thermistor sensor itself is also a straightforward part swap for experienced DIYers. However, if the control board is involved or the wiring damage is extensive, professional service is recommended.

Continuing to run the unit with an active thermistor short means the control board cannot accurately read temperatures in the affected zone. This could result in inconsistent cooling or food safety concerns if the zone fails to maintain proper temperature. It is best to address the fault promptly rather than operating the refrigerator in a degraded state.