Kenmore Refrigerator Error Code R4

R4 means the control board has detected an open or short circuit in the ambient room temperature sensor, also called the RT sensor. This sensor measures the air temperature around the outside of the refrigerator and feeds that data to the control board. When the board reads no signal or an invalid signal from this sensor, it triggers R4 to alert you to the fault.

The refrigerator may continue running in a default mode, but cooling performance can be unreliable because the control board is missing ambient temperature data it uses to regulate the compressor. Food safety becomes a concern if temperatures are not being maintained accurately. You can monitor actual compartment temperatures with a thermometer short-term, but the underlying fault should be repaired promptly to avoid food spoilage or component overwork.

Disconnect the RT sensor connector and use a multimeter set to the ohms range to measure resistance across the sensor's two terminals. Most NTC thermistors used as RT sensors read roughly 10,000 ohms at room temperature (around 77 degrees F / 25 degrees C), though your specific model's service data will give the exact spec. A reading of infinite resistance indicates an open circuit and a failed sensor. A reading near zero ohms indicates a short. Either result means the sensor should be replaced.

Start by unplugging the refrigerator and locating the RT sensor connector, then check that it is fully seated and free of corrosion. If the connection looks good, use a multimeter to test the sensor's resistance and compare it to the spec in your service manual. A sensor reading open or near zero ohms needs to be replaced. If the sensor tests fine, inspect the wiring harness between the sensor and the control board for damage before considering a board replacement.

If the fix is a loose connector, there is no parts cost and only your time. A replacement RT sensor thermistor typically costs between $15 and $40 for the part. If the wiring harness needs replacement the part can range from $20 to $80. A main control board, which is the least likely cause, generally runs $100 to $250 for the part. Labor from a technician adds $75 to $150 per hour if you hire out the repair.