Sub-Zero Freezer Error Code t4: Thermistor 2... | appliancefaults.com

Technical Background:

The electronic control board (MCU) monitors the freezer temperature using thermistor 2. The thermistor's resistance changes with temperature. The MCU reads the voltage drop across the thermistor, which is converted to a temperature reading. If the reading is out of range (too high or too low), the MCU will trigger error code t4, indicating a problem with the thermistor circuit.

Symptoms:

The Sub-Zero refrigerator displays error code t4. The freezer temperature may be erratic or warmer than the setpoint. The unit may cycle on and off frequently. Ice buildup may occur in the freezer compartment.

Possible Causes:

Defective freezer thermistor 2
Wiring harness damage between the thermistor and the electronic control board
Poor connection at the thermistor or control board connector
Faulty electronic control board (MCU)
Ice buildup around the thermistor affecting readings

Solution:

1

Disconnect power to the Sub-Zero at the breaker panel.
2

Locate freezer thermistor 2, usually near the evaporator coil, behind the back panel inside the freezer.
3

Inspect the wiring harness and connectors for any visible damage or corrosion.
4

Using a multimeter, measure the resistance of the thermistor. Compare the reading to the thermistor's temperature-resistance chart (available in the service manual).
5

If the thermistor is out of range, replace it with a new, OEM Sub-Zero thermistor.
6

If the wiring and thermistor are good, suspect a faulty electronic control board. Replace the control board with a new, OEM Sub-Zero control board.
7

Restore power and verify the error code is cleared.

Safety Warning:

Always disconnect power to the appliance at the breaker panel before attempting any repairs. High voltage is present inside the unit and can cause serious injury or death. Follow Lock-Out/Tag-Out (LOTO) procedures.

Prevention:

Periodically defrost the freezer to prevent excessive ice buildup. Inspect the wiring harness and connectors for any signs of damage. Use OEM replacement parts to ensure proper operation.

Expert Tip:

Some Sub-Zero models have a service mode. To enter service mode, press and hold the 'Door Alarm' and 'Max Ice' buttons simultaneously for 5 seconds. This allows you to run diagnostic tests and view sensor readings in real-time.

Frequently Asked Questions

•Where can I find the temperature-resistance chart for the freezer thermistor?

The temperature-resistance chart is typically located in the Sub-Zero service manual for your specific model. You can often find these manuals online or purchase them from appliance parts suppliers.

•What is the typical resistance range I should expect from a good thermistor at 32°F?

While the exact resistance varies by model, a good thermistor at 32°F (0°C) typically reads between 5,000 and 10,000 ohms. Refer to the service manual for your specific model's chart for accurate values.

•If the error code returns after replacing the thermistor, what should I check next?

If the error code returns, double-check the wiring harness for any hidden damage or breaks. Also, carefully inspect the connector at the electronic control board for corrosion or loose pins. It's possible the board itself is still the issue, despite replacing the thermistor.

Sub-Zero Freezer Error Code t4: Thermistor 2 Troubleshooting Guide

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip:

Frequently Asked Questions

•Where can I find the temperature-resistance chart for the freezer thermistor?

•What is the typical resistance range I should expect from a good thermistor at 32°F?

•If the error code returns after replacing the thermistor, what should I check next?

Related questions

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip: