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Error code reference

LG Refrigerator Error Code CO E

Communication error between Micom of Main PCB and Display Micom

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Communication error between Micom of Main PCB and Display Micom. Possible causes include poor communication connection, poor TR of transmitter and receiver Tx/Rx between display and main board.

First step from the service manual

Check for loose connections, then check voltage at Display PCB CON101 pins 7-6 for 12V and CON101 pins 3-6 for 5V.

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

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What CO E means on a LG refrigerator

The CO E error code on an LG refrigerator indicates a communication failure between the main PCB's microcontroller (Micom) and the display board's Micom. These two control units rely on a serial data link using transmit (Tx) and receive (Rx) signal lines. When this communication link breaks down or produces out-of-range signals, the main board can no longer exchange operational data with the display, triggering the CO E fault. The display may go blank, freeze, or show the error continuously even if the refrigerator is otherwise cooling normally.

The two most common root causes are physical connection issues and transistor-level failures on the Tx/Rx circuit. Loose, corroded, or damaged connector pins at the ribbon or wire harness between the display board and the main PCB are the first thing to rule out. On the display PCB, connector CON101 is the key junction point. Pins 7 and 6 on CON101 should supply 12V for board power, while pins 3 and 6 should supply 5V for logic-level communication. If either voltage is absent or out of tolerance, the communication circuit cannot function correctly regardless of connector integrity.

Beyond connector and power supply checks, the transistors responsible for driving the Tx and Rx signal lines on either the display board or the main PCB can degrade or fail, disrupting the data signal even when power supply voltages appear correct. In those cases, one or both boards will require replacement. Because the fault can originate on either side of the communication link, systematic voltage and continuity checks are necessary before ordering parts.

Source: manufacturer service documentation.

Common causes of CO E

  1. 01

    Loose or disconnected wiring harness

    Wiring / connection

    The connector linking the display board and the main PCB can work loose over time due to vibration or handling. Inspect the harness at CON101 on the display PCB and at the corresponding main board connector for any unseated, bent, or corroded pins.

  2. 02

    Missing or low supply voltage at CON101

    Wiring / connection

    If CON101 pins 7-6 are not delivering 12V or pins 3-6 are not delivering 5V, the display Micom cannot operate or communicate. Use a multimeter to confirm both voltages are present and within tolerance before replacing any boards.

  3. 03

    Failed Tx/Rx transistor on display PCB

    Part replacement

    The transistors that drive the transmit and receive data lines on the display board can fail, cutting off the serial communication signal even when power voltages are correct. This typically requires display PCB replacement.

  4. 04

    Failed Tx/Rx transistor on main PCB

    Part replacement

    The main board contains its own Tx/Rx transistors for the communication link. If the display board checks out but the CO E error persists, the fault may lie on the main PCB side, requiring main board replacement.

  5. 05

    Damaged or shorted wiring between boards

    Part replacement

    A wire in the harness between the display and main board can develop a short or open circuit due to pinching, chafing, or heat exposure. Visually inspect the full length of the harness and test continuity on each conductor.

See the test procedure for each cause

Frequently asked questions about CO E

What does CO E mean on a LG refrigerator?
CO E indicates a communication error between the main PCB's Micom and the display board's Micom. The two boards exchange data over a serial link using Tx and Rx signal lines, and when that link is disrupted the CO E code is triggered. Possible causes include loose wiring connectors, missing power supply voltages at the display PCB, or failed transistors on either board.
Can I fix the CO E error myself without a technician?
Some cases can be resolved without professional help. Start by unplugging the refrigerator, checking that the wiring harness connectors between the display and main board are fully seated, and looking for any visibly damaged wires. If connections appear secure, checking voltages at CON101 on the display PCB requires a multimeter and some comfort working around electronics. Board-level transistor failures generally require component or board replacement and may be better handled by a technician.
Will resetting the refrigerator clear the CO E error?
A power reset by unplugging the unit for a few minutes may temporarily clear the code if the cause was a transient communication glitch. However, if the underlying issue is a loose connector, failed transistor, or missing supply voltage, the CO E error will return once power is restored. A reset is worth trying as a first step, but a persistent code requires proper diagnosis.
Is it safe to keep using my LG refrigerator while it shows CO E?
The refrigerator may continue cooling normally even while displaying CO E, since the error relates to the communication link rather than the compressor or sealed system. However, with the display and controls potentially unresponsive, you may not be able to adjust settings or receive alerts for other faults. It is best to address the error promptly to avoid food safety issues if other problems go undetected.
How much does it cost to repair a CO E error on an LG refrigerator?
If the fix is simply reseating a loose connector, there may be no parts cost at all beyond a service call fee, which typically ranges from around 75 to 150 dollars. Display PCB replacement can run anywhere from 100 to 250 dollars for the part alone, while main PCB replacement tends to cost between 150 and 400 dollars depending on the model. Labor charges vary by region, so getting a diagnosis before authorizing parts replacement helps avoid unnecessary expense.

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