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Error code reference

Dacor Oven Error Code U42

Upper/single relay board E2 checksum failure.

Dacor codesDacor oven codes

Upper/single relay board E2 checksum failure.

First step from the service manual

Replace relay board.

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

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What U42 means on a Dacor oven

The U42 error code on a Dacor oven indicates an E2 checksum failure on the upper or single oven relay board. A checksum is a validation mechanism used by the control system to verify that data stored in the relay board's non-volatile memory (EEPROM or similar) is intact and uncorrupted. When the checksum value calculated at startup does not match the stored reference value, the board flags this as a critical fault and triggers the U42 code. This means the relay board's internal memory has become corrupted or the board itself has failed.

The relay board is a core component responsible for controlling high-voltage switching operations in the oven, including bake and broil elements, convection fan relays, and other load circuits. Unlike a simple sensor fault, an E2 checksum failure points directly to the relay board's own internal firmware or memory state rather than any external wiring or peripheral component. Power surges, voltage spikes on the supply line, or component aging on the board can all corrupt stored memory values and produce this fault.

Because the failure is internal to the relay board's memory or logic circuitry, there is no practical field-level repair for the memory corruption itself. The recommended first diagnostic step is direct replacement of the upper or single relay board. Before replacement, technicians should verify that supply voltage to the board is within specification and that there are no signs of burning, arcing, or physical damage on the board that might indicate a broader electrical issue in the oven.

Source: manufacturer service documentation.

Common causes of U42

  1. 01

    Relay board EEPROM or memory corruption

    Part replacement

    The internal memory on the relay board has become corrupted, causing the checksum validation to fail at startup. This is the primary cause of U42 and requires relay board replacement.

  2. 02

    Voltage spike or power surge

    Part replacement

    A surge on the household power supply can corrupt non-volatile memory on the relay board. Check for evidence of surge damage on the board such as discoloration or burnt components.

  3. 03

    Relay board component failure due to age or heat

    Part replacement

    Long-term exposure to the heat environment inside the oven can degrade relay board components over time, leading to memory faults and checksum errors.

  4. 04

    Intermittent power loss during a write cycle

    Wiring / connection

    If power to the oven was interrupted while the relay board was writing data to memory, the stored values may be left in a corrupted state. A power cycle may occasionally clear this, but board replacement is typically still needed.

See the test procedure for each cause

Frequently asked questions about U42

What does U42 mean on a Dacor oven?
U42 indicates an E2 checksum failure on the upper or single oven relay board. The control system has detected that data stored in the relay board's internal memory is corrupted or invalid. This is a hardware-level fault pointing directly to the relay board rather than any external sensor or wiring. Relay board replacement is the recommended repair.
Can I fix a U42 error on my Dacor oven myself?
Because the fault is internal to the relay board's memory, there are no field-level repairs that can restore the board to working condition. A technician or experienced DIYer can replace the relay board, but working with oven components involves high-voltage wiring and should only be done with the oven fully disconnected from power. If you are not comfortable working with high-voltage appliances, professional service is recommended.
Will resetting the oven clear the U42 error code?
A power reset by turning off the circuit breaker for several minutes may temporarily clear the code in rare cases where power interruption caused the checksum failure. However, if the relay board's memory is genuinely corrupted or the board has failed, the U42 error will return after reset. Board replacement is the definitive fix.
Is it safe to use my Dacor oven while the U42 code is active?
A U42 checksum failure means the relay board controlling the heating elements and other load circuits has an unverified internal state. Operating the oven in this condition is not recommended, as the board may not switch loads correctly or predictably. The oven should be taken out of service until the relay board is replaced.
How much does it cost to repair a Dacor oven with a U42 error?
Repair costs depend on the specific Dacor model and the current price of the relay board part. As a general range, relay board parts for built-in ovens can cost anywhere from $150 to $400 or more, with professional labor adding another $100 to $250 depending on your region. Total repair costs typically fall in the range of $250 to $650 when serviced by a technician.

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