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Error code reference

Maytag Oven Error Code 3d21

Runaway temperature with door locked

Maytag codesMaytag oven codes

Runaway temperature with door locked — sensor resistance indicates abnormal temperature condition while door is in locked state.

First step from the service manual

Check sensor resistance (expected ~1100 ohms at 75°F/24°C).

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

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What 3d21 means on a Maytag oven

Error code 3d21 indicates the control board has detected a short circuit in the temperature sensor circuit for the upper or single oven cavity. A shorted sensor means the resistance across the sensor has collapsed to 0 ohms, which is outside any valid operating range. The control board cannot derive a usable temperature reading from a sensor in this condition and will trigger the fault to prevent uncontrolled heating. The sensor involved is a resistance-based temperature sensor (RTD-type) that should read approximately 1080 ohms at room temperature (70°F).

For homeowners, the temperature sensor is a small probe mounted inside the oven cavity, usually at the back wall. It tells the control board how hot the oven is so the board can cycle the heating elements on and off accurately. When the sensor shorts internally or through damaged wiring, it sends an invalid signal that the board interprets as a fault. This is why the oven stops operating and displays 3d21. The fix usually involves replacing the sensor or repairing the wiring connecting it to the control board, and the repair is manageable for a confident DIYer with a multimeter.

Source: manufacturer service documentation.

Common causes of 3d21

  1. 01

    Failed temperature sensor (internal short)

    Part replacement

    The RTD temperature sensor itself has developed an internal short, causing resistance to drop to 0 ohms. This is the most common cause and is confirmed by measuring sensor resistance directly at the sensor connector.

  2. 02

    Pinched or shorted sensor wiring harness

    Part replacement

    The wiring harness between the temperature sensor and the control board has been pinched, burned, or abraded until two conductors contact each other, creating a short. Inspect the full length of the harness for damage, especially near the oven cavity wall and any sharp metal edges.

  3. 03

    Moisture or grease contamination at sensor connector

    Wiring / connection

    Grease or moisture inside the sensor connector can create a conductive path between terminals, producing an apparent short at the control board. Disconnecting and cleaning the connector may resolve this without replacing the sensor.

  4. 04

    Faulty control board misreading the sensor circuit

    Part replacement

    If the sensor and wiring test within spec but 3d21 persists, the control board's input circuit for the sensor may have failed and is falsely reporting a short. This is the least likely cause and should only be suspected after the sensor and harness are confirmed good.

See the test procedure for each cause

Frequently asked questions about 3d21

What does error code 3d21 mean on a Maytag oven?
Code 3d21 means the control board has detected that the upper or single oven temperature sensor is shorted, with resistance reading 0 ohms. A healthy sensor reads around 1080 ohms at room temperature (70°F). A reading of 0 ohms tells the board the sensor circuit has failed and the oven cannot regulate temperature accurately.
How do I fix error code 3d21 on a Maytag oven?
Start by unplugging the oven and locating the temperature sensor inside the oven cavity, typically mounted at the rear wall. Disconnect the sensor connector and measure resistance across the sensor terminals with a multimeter. If you read 0 ohms, the sensor is shorted and needs to be replaced. If the sensor reads correctly near 1080 ohms, inspect the wiring harness from the sensor to the control board for damage or shorts before assuming the board is at fault.
Is it safe to use my Maytag oven while error code 3d21 is active?
No. With a shorted temperature sensor, the control board cannot accurately monitor oven temperature. Depending on how the board responds to the fault, the oven may not heat at all, or in a worst case, heating elements could operate without proper temperature feedback. Do not use the oven for cooking until the sensor or wiring is repaired.
How much does it cost to fix a Maytag oven showing 3d21?
A replacement oven temperature sensor typically costs between $20 and $60 for the part, and replacing it is a repair most DIYers can complete in under 30 minutes using a screwdriver. If the wiring harness is damaged, a harness repair or replacement adds some cost and complexity. Professional appliance technician labor generally runs $100 to $200 depending on your area, making the total repair cost modest compared to replacing the oven.
Can a bad wiring harness cause the 3d21 code on a Maytag oven?
Yes. If the wires running from the temperature sensor to the control board are pinched, burned, or have bare conductors touching each other, the board will see 0 ohms on the sensor circuit and trigger 3d21 even if the sensor itself is fine. Always test resistance at the sensor connector first, then at the control board end of the harness to isolate where the short is located.

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