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Error code reference

GE Oven Error Code C4

Communication fail with lower relay board.

GE codesGE oven codes

Communication fail with lower relay board.

First step from the service manual

Check harness first and then replace component indicated by Cx error code.

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

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What C4 means on a GE oven

The C4 error code on a GE oven indicates a communication failure between the main control board and the lower relay board. In double oven configurations and certain single-cavity models, the lower relay board serves as an intermediary component that receives switching commands from the main control and energizes the bake, broil, and convection heating elements in the lower cavity. When the main board cannot establish or maintain proper serial communication with this relay board, it registers C4 and typically halts operation to prevent uncontrolled heating.

The communication link between the main control and the lower relay board runs through a wiring harness that carries both power and data signals. Failures in this circuit most commonly originate from harness-related issues: connectors that have worked loose due to vibration, terminals that have corroded or been damaged by heat exposure, or wires that have developed breaks or shorts from being pinched or routed too close to a heat source. Because the oven cavity operates at high temperatures, harness degradation is a realistic and common failure mode over time.

Diagnosis should begin with a thorough inspection of the wiring harness running between the main control board and the lower relay board. Check each connector for secure seating, inspect terminals for corrosion or burn marks, and trace the harness for any signs of chafing, melting, or pinching. If the harness checks out intact and all connections are secure, the lower relay board itself is the next suspect and will likely require replacement to resolve the fault.

Source: manufacturer service documentation.

Common causes of C4

  1. 01

    Loose or disconnected wiring harness connector

    Wiring / connection

    Vibration and repeated heating cycles can cause connectors between the main board and lower relay board to loosen or partially unseat. Inspect both ends of the harness and firmly reseat each connector to confirm this is not the cause.

  2. 02

    Damaged or corroded harness wiring

    Part replacement

    Wires routed near high-heat areas can melt, crack, or corrode over time, interrupting the communication signal. Look for discoloration, brittle insulation, burn marks, or broken wires along the full length of the harness.

  3. 03

    Failed lower relay board

    Part replacement

    If the harness and all connectors are in good condition, the lower relay board itself may have failed internally. A board with burned components or failed communication circuitry will need to be replaced.

  4. 04

    Faulty main control board

    Part replacement

    Less commonly, the main control board may be unable to send the communication signal correctly. This is typically considered after the harness and lower relay board have been ruled out as the source of the fault.

See the test procedure for each cause

Frequently asked questions about C4

What does C4 mean on a GE oven?
C4 on a GE oven means the main control board has detected a communication failure with the lower relay board. The lower relay board is responsible for controlling the heating elements in the lower oven cavity. The fault can be caused by a loose harness connection, damaged wiring, or a failed relay board. The oven will typically not operate normally while this code is active.
Can I fix a C4 error on my GE oven myself?
The first step is always inspecting the wiring harness and connectors between the main board and the lower relay board, which is a task many experienced DIYers can perform after disconnecting power to the unit. If the harness is intact and connectors are secure, resolving the fault will require replacing the lower relay board, which involves working inside the control area of the oven. Anyone uncomfortable working around electrical components should contact a qualified appliance technician.
Is it safe to use my GE oven when it shows a C4 error?
A C4 error indicates that the main control board cannot communicate with the lower relay board, which means the oven may not control its heating elements properly. Using the oven in this condition is not recommended, as the control system may be unable to regulate temperature or shut off heating elements correctly. The oven should be kept off until the fault is diagnosed and repaired.
Will resetting my GE oven clear the C4 error code?
Resetting the oven by cutting power at the breaker for a few minutes may temporarily clear the C4 code, but it will return if the underlying communication problem has not been corrected. A persistent C4 code after a reset points to a real hardware fault in the harness or the lower relay board that needs to be physically inspected and repaired.
How much does it cost to repair a GE oven C4 error?
If the fix is simply reseating a loose connector, there may be no parts cost at all, though a service call will typically run between $75 and $150 for the diagnostic visit. If the lower relay board needs replacement, parts costs can range from $80 to $200 or more depending on the specific model, plus labor if a technician performs the repair. Harness replacement costs will fall somewhere in between, depending on part availability and the extent of the damage.

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