GE Microwave Error Code Upper Thermal Sensor OPEN

This error means the Smart Board has detected an open circuit in the upper thermistor, a temperature sensor located in the upper cavity area of the microwave. The board expects to see approximately 100K ohms of resistance from the thermistor at room temperature through the blue and white wires at connector CN09. An open circuit reading indicates the thermistor has failed internally or its wiring connection has been broken. The microwave will not operate normally until the fault is resolved.

No, you should not continue using the microwave while the Upper Thermal Sensor OPEN error is active. The upper thermistor is part of the thermal protection system, and without accurate temperature monitoring the microwave cannot protect against overheating conditions. Operating the unit in this state poses a risk of undetected overheating and potential damage to internal components.

Repair costs vary depending on which component has failed. A replacement upper thermistor is generally an inexpensive part, typically in the range of $10 to $40. If the Smart Board requires replacement, parts costs rise significantly, often falling in the $80 to $200 range depending on the model. Professional labor charges for microwave repair typically add $75 to $150 or more, so factoring in the age and value of the microwave before committing to board-level repairs is advisable.

A knowledgeable DIYer can perform the initial diagnostics, which involve unplugging the microwave, locating connector CN09 on the Smart Board, and measuring resistance across the blue and white thermistor wires with a multimeter. If the wiring is loose or the connector is corroded, reseating or cleaning the connection may resolve the issue without parts. If the thermistor itself reads infinite resistance, replacing the upper thermistor is the required repair. Working inside a microwave involves high-voltage components, so the unit must always be unplugged before opening the cabinet.

A power reset by unplugging the microwave for a few minutes may temporarily clear the error display, but the fault will return as soon as the control board checks the sensor circuit again. Because the error reflects an actual electrical condition in the thermistor circuit, the underlying cause must be diagnosed and repaired. A reset alone is not a fix.