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Error code reference

Maytag Microwave Error Code E21

Thermal sensor open error.

Maytag codesMaytag microwave codes

Thermal sensor open error.

First step from the service manual

Check if sensor is unplugged; inspect wiring and PCB assembly.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E21 means on a Maytag microwave

E21 on a Maytag microwave indicates the control board has detected an open circuit condition in the thermal sensor circuit. The thermal sensor monitors internal cavity temperature during cooking cycles. An open circuit means the board is receiving no signal from the sensor, which it interprets as a broken or disconnected sensing element rather than a temperature reading. This triggers the E21 fault and halts normal operation to prevent uncontrolled heating.

For homeowners, this means the microwave's built-in temperature monitoring system has lost contact with the part that tells it how hot the interior is getting. Without that data, the microwave cannot safely regulate its heating cycles, so it shuts down and displays E21. This is a protective response, not a sign of catastrophic damage. The most common reasons this happens are a loose or disconnected sensor wire, a damaged wiring harness between the sensor and the PCB assembly, or a failed thermal sensor that has broken internally and can no longer conduct a signal. Identifying which of these three conditions is present determines the repair path.

Source: manufacturer service documentation.

Common causes of E21

  1. 01

    Disconnected thermal sensor connector

    Wiring / connection

    The wire connector linking the thermal sensor to the wiring harness may have vibrated loose or come unplugged during prior service. This immediately creates an open circuit and triggers E21 without any component failure.

  2. 02

    Failed thermal sensor

    Part replacement

    The thermal sensor itself may have failed internally, breaking the circuit even though it remains physically connected. A failed sensor will show infinite resistance when tested with a multimeter, confirming it needs replacement.

  3. 03

    Damaged wiring harness between sensor and PCB

    Part replacement

    A wire in the harness running from the thermal sensor to the PCB assembly may be broken, pinched, or burned. This severs the signal path and produces the same open circuit condition the board reads as E21.

  4. 04

    Faulty PCB assembly

    Part replacement

    If the sensor and all wiring test correctly, the PCB assembly itself may have a damaged input circuit that cannot read the sensor signal. This is the least likely cause and should only be considered after the sensor and harness have been ruled out.

See the test procedure for each cause

Frequently asked questions about E21

What does E21 mean on a Maytag microwave?
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.
How do I fix E21 on a Maytag microwave?
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.
Is it safe to use my Maytag microwave when E21 is displayed?
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.
How much does it cost to fix a Maytag microwave E21 error?
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.
Can I test the thermal sensor myself to diagnose E21?
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.

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