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Error code reference

Maytag Microwave Error Code Err4

Failed H.V

Maytag codesMaytag microwave codes

Failed H.V. Board, Shorted Touch Panel, or Wrong jumper setting.

First step from the service manual

Replace H.V. Board; check Touch Panel; check cable to H.V. Board.

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

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  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
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What Err4 means on a Maytag microwave

Err4 on a Maytag microwave indicates the control board has detected a failure in the high voltage (H.V.) board. The H.V. board is responsible for converting standard household current into the high-voltage power needed to drive the magnetron, which is the component that generates microwave energy. When the control board cannot confirm proper operation of the H.V. board, it locks out the cooking function and throws this error. The fault can stem from a failed H.V. board component, a damaged board due to electrical surge, or a complete board failure.

For homeowners, the H.V. board is essentially the power converter inside your microwave. Without it working correctly, the microwave cannot produce the energy needed to heat food. When Err4 appears, your microwave will not cook. The control board detected something wrong with this converter and shut down the system to prevent further damage or a safety hazard. The high-voltage system inside a microwave carries lethal voltage levels, even after the unit is unplugged, due to capacitors that store charge. Any hands-on repair involving this system should be approached with serious caution or handed off to a qualified technician.

Source: manufacturer service documentation.

Common causes of Err4

  1. 01

    Failed H.V. board

    Part replacement

    The high voltage board itself has failed internally, either from component burnout, a shorted diode or capacitor on the board, or general wear. This is the primary cause indicated by Err4 and requires board replacement to resolve.

  2. 02

    Electrical surge damage to H.V. board

    Part replacement

    A power surge or spike can damage the H.V. board's internal components without visibly burning the board. The board may appear intact but fail to function correctly, triggering Err4.

  3. 03

    Loose or damaged wiring connection to H.V. board

    Wiring / connection

    A connector that has come loose or a wire that has burned or corroded where it meets the H.V. board can interrupt communication or power to the board, causing the control board to log a failure. Inspect all harness connections to the H.V. board before replacing the board itself.

  4. 04

    Control board misreading H.V. board status

    Part replacement

    In some cases the main control board itself is faulty and incorrectly reporting an H.V. board failure when the H.V. board is actually functional. This is less common but worth considering if a confirmed-good replacement H.V. board still triggers Err4.

See the test procedure for each cause

Frequently asked questions about Err4

What does Err4 mean on a Maytag microwave?
Err4 means the microwave's control board has detected a failure in the high voltage (H.V.) board. The H.V. board converts household current into the high-voltage power required to run the magnetron and heat food. When this board fails or loses communication, the microwave shuts down cooking functions and displays Err4.
How do I fix Err4 on a Maytag microwave?
The primary fix for Err4 is replacing the high voltage board. Before ordering a part, unplug the microwave and check that all wiring harness connectors to the H.V. board are fully seated and undamaged. If connections are secure and the board shows visible burn marks or damage, replace the H.V. board. Because the high-voltage capacitor inside a microwave can hold a lethal charge even after unplugging, discharging the capacitor before any internal work is mandatory. If you are not experienced with high-voltage electronics, a qualified appliance technician should handle this repair.
Is it safe to use my Maytag microwave when Err4 is displayed?
No. Err4 indicates the high voltage board has failed, and the microwave will not heat food in this state. Attempting to force the unit to run with a known H.V. board fault is not safe and can cause further damage to other components. Stop using the microwave until the H.V. board is inspected and replaced.
How much does it cost to fix Err4 on a Maytag microwave?
A replacement Maytag high voltage board typically costs between $50 and $150 depending on the specific model. If you hire a technician, expect to add $75 to $150 or more in labor, bringing the total repair cost to roughly $125 to $300. For older or lower-cost microwaves, compare the repair cost against replacement before committing, since the H.V. board is one of the more expensive internal components.
Can unplugging my Maytag microwave reset the Err4 code?
Unplugging the microwave and plugging it back in may temporarily clear the error display, but Err4 will return as soon as the control board checks the H.V. board again and confirms the fault. A power cycle does not fix a failed H.V. board. The error will persist until the board is replaced or the underlying fault is corrected.

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