Maytag Microwave Error Code E21

E21 means the control board detected an open circuit in the thermal sensor circuit, meaning it is receiving no signal from the sensor that monitors interior cavity temperature. The microwave shuts down cooking functions when this happens because it cannot safely regulate heat without temperature feedback. The fault points to a disconnected sensor wire, a broken wiring harness, a failed sensor, or less commonly a faulty PCB assembly.

No, you should not continue using the microwave while E21 is active. The error means the unit has lost its ability to monitor internal temperature, which is a core safety function. Operating without working thermal monitoring risks overheating the cavity or internal components. Keep the microwave unplugged until the sensor circuit issue is resolved.

Yes, this is a practical DIY test. Unplug the microwave, access the thermal sensor, and disconnect it from the harness. Set a multimeter to the resistance or continuity setting and probe both terminals of the sensor. A functional sensor will show a measurable resistance value, while a failed open sensor will read OL or infinite resistance. If the sensor passes this test, move on to checking the harness wiring and the PCB assembly connector.

Start by unplugging the microwave and locating the thermal sensor, which is typically mounted on the interior cavity wall. Check whether the sensor connector is fully seated and the wiring harness shows no visible damage or burn marks. If connections look good, use a multimeter to test the sensor for continuity; a reading of infinite resistance confirms the sensor has failed and needs replacement. If the sensor tests fine, inspect the harness wiring and PCB assembly connector pins for damage.

If the fix is simply reseating a loose connector, the repair costs nothing beyond your time. A replacement thermal sensor typically costs between $15 and $40 for the part. If the wiring harness needs replacement, parts usually run $20 to $60 depending on the model. A new PCB assembly is the most expensive outcome, often $80 to $200 for the part alone, and at that price point it is worth comparing the repair cost against the cost of a replacement microwave.