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Error code reference

Kenmore Range Error Code 21

LIN (Local Interconnect Network) error

Kenmore codesKenmore range codes

LIN (Local Interconnect Network) error — no communications or shorted bus.

First step from the service manual

Verify the LIN Bus communication harness at ESEC-UIB, P9 connector is well connected and not damaged.

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

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What 21 means on a Kenmore range

Error code 21 on a Kenmore range indicates a failure in the LIN (Local Interconnect Network) communication bus. The LIN bus is a serial communications protocol used to pass data between the Electronic Surface Element Control (ESEC) board and the User Interface Board (UIB). When the control system detects either a complete loss of communication or a shorted condition on this bus, it triggers error code 21 and halts normal operation to prevent unsafe behavior.

The LIN bus relies on a dedicated wiring harness connecting the ESEC and UIB, with the P9 connector at the ESEC-UIB junction serving as the primary interface point. A shorted bus occurs when the LIN signal wire comes into contact with ground or another conductor, collapsing the voltage signal that the boards use to communicate. A total communication loss can result from a broken wire, corroded connector pins, or a failed component on either board that drives or reads the LIN signal.

Diagnosing this error begins at the P9 connector on the ESEC-UIB harness. The connector should be fully seated, free of corrosion, and show no signs of heat damage or wire breakage at the strain relief points. If the harness and connector check out, the fault may lie within the ESEC board or the UIB itself, as either board could be responsible for corrupting the bus signal.

Source: manufacturer service documentation.

Common causes of 21

  1. 01

    Loose or disconnected P9 connector

    Wiring / connection

    The LIN bus harness at the P9 connector on the ESEC-UIB may have worked loose over time due to vibration or a previous repair. Inspecting and firmly reseating this connector is the first required step.

  2. 02

    Damaged LIN bus wiring harness

    Part replacement

    The harness connecting the ESEC and UIB boards may have a broken wire, pinched section, or burned insulation that is interrupting or shorting the LIN signal. Visually trace the harness and check for continuity through each conductor.

  3. 03

    Corroded or damaged connector pins

    Part replacement

    Corrosion, bent pins, or heat damage at the P9 connector terminals can prevent a reliable electrical connection on the LIN bus. Inspect the pins closely and clean or replace the connector as needed.

  4. 04

    Failed User Interface Board (UIB)

    Part replacement

    If the wiring and connectors are intact, the UIB may have an internal fault that prevents it from communicating on the LIN bus. A failed UIB will require board replacement to restore communication.

  5. 05

    Failed ESEC board

    Part replacement

    The Electronic Surface Element Control board itself can fail in a way that shorts or disables the LIN bus signal. If all wiring and the UIB have been ruled out, the ESEC board is the likely source of the fault.

See the test procedure for each cause

Frequently asked questions about 21

What does 21 mean on a Kenmore range?
Error code 21 on a Kenmore range indicates a LIN (Local Interconnect Network) communication error between the Electronic Surface Element Control board and the User Interface Board. The fault is triggered when the control system detects either no communication or a shorted condition on the LIN bus. The range will not operate normally until the underlying communication failure is resolved.
How do I fix error code 21 on a Kenmore range?
Start by inspecting the LIN bus harness at the P9 connector on the ESEC-UIB and confirm it is fully seated and undamaged. If the connector looks good, trace the harness for any pinched, broken, or burned wiring. If the wiring is intact, testing or replacing the UIB or ESEC board may be necessary to resolve the fault.
Will resetting the Kenmore range clear error code 21?
A power reset by cutting power at the breaker for a few minutes may temporarily clear the error if the communication disruption was caused by a transient voltage event. However, if there is a physical fault such as a loose connector, damaged wiring, or a failed board, the error code 21 will return after the reset. A reset alone is not a repair.
Is it safe to use my Kenmore range while error code 21 is displayed?
It is not recommended to continue using the range while this error is active. A LIN bus fault means the control boards cannot communicate reliably, which could result in surface elements not responding correctly to commands. Discontinue use until the communication fault has been diagnosed and repaired.
How much does it cost to repair error code 21 on a Kenmore range?
If the fix is simply reseating a loose connector, there may be no parts cost, though a service call can range from $75 to $150 for labor. If a wiring harness needs replacement, parts and labor combined typically range from $100 to $250. Board replacements, either the UIB or the ESEC, can bring total repair costs to a range of $200 to $450 or more depending on parts availability and labor rates.

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