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Error code reference

LG Refrigerator Error Code E CO

Communication error between Micom of Main PCB and Display Micom, caused by poor communication connection or…

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Communication error between Micom of Main PCB and Display Micom, caused by poor communication connection or 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 CON101 pins 5-6 for 12V.

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

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What E CO means on a LG refrigerator

The E CO 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 controllers rely on a continuous data link to coordinate refrigerator operation, display readings, and respond to user input. When that link is interrupted or degraded, the system flags E CO to alert the technician that the internal serial communication channel has broken down.

The root cause typically falls into one of two categories: a physical connection problem or a component-level failure in the transmitter/receiver (Tx/Rx) circuitry. On the physical side, loose, corroded, or damaged wiring harness connectors between the display board and the main board are the most frequent culprits. On the component side, a failed transistor acting as the signal driver or receiver within the Tx/Rx stage can prevent data packets from being sent or acknowledged correctly, even when the wiring appears intact.

Diagnosis should begin at connector CON101 on the main PCB. Pins 5 and 6 of CON101 should read 12V, confirming that the communication bus is properly powered. If the voltage is absent or outside that expected range, the fault likely lies upstream in the power supply section of the main board. If voltage is present but the error persists, attention should shift to the integrity of the harness connectors and the Tx/Rx transistor components on either the main or display PCB.

Source: manufacturer service documentation.

Common causes of E CO

  1. 01

    Loose or disconnected wiring harness

    Wiring / connection

    The connector linking the display board to the main PCB can work loose over time due to vibration. Inspect all harness connectors along the communication path and reseat any that show movement or play.

  2. 02

    Absent or low voltage at CON101 pins 5-6

    Part replacement

    The communication bus requires 12V at pins 5 and 6 of connector CON101 on the main board. A missing or low voltage reading at these pins points to a power supply fault on the main PCB that must be resolved before communication can be restored.

  3. 03

    Failed Tx/Rx transistor on the display board

    Part replacement

    The transmitter and receiver stage on the display board uses transistors to send and receive data signals. A failed transistor in this circuit will block communication even when all wiring and power supply checks pass, requiring display board replacement.

  4. 04

    Failed Tx/Rx transistor on the main PCB

    Part replacement

    The same Tx/Rx transistor circuitry exists on the main control board side. If the display board tests out correctly, a shorted or open transistor on the main PCB may be responsible for the communication breakdown.

  5. 05

    Corroded or damaged connector pins

    Wiring / connection

    Moisture exposure or age can corrode the pins inside the harness connectors, increasing resistance and degrading the signal. Visually inspect CON101 and related connectors for discoloration, oxidation, or bent pins.

See the test procedure for each cause

Frequently asked questions about E CO

What does E CO mean on a LG refrigerator?
E CO indicates a communication error between the main PCB's Micom and the display board's Micom. The two control boards have lost their data link, which can be caused by a loose wiring connection or a failed transistor in the Tx/Rx circuitry on either board. The first diagnostic step is to check for loose connectors and then verify that 12V is present at pins 5 and 6 of connector CON101 on the main board.
Can I fix the E CO error myself, or do I need a technician?
Reseating loose harness connectors is a straightforward task most homeowners can handle safely with the refrigerator unplugged. However, diagnosing a failed Tx/Rx transistor or a faulty PCB requires a multimeter, familiarity with reading circuit boards, and the ability to safely work with appliance electronics. If basic connector checks do not clear the error, a qualified technician should perform the component-level diagnosis.
Is it safe to keep using my refrigerator while it shows the E CO error?
A communication failure between the main board and display board can prevent the refrigerator from responding correctly to temperature commands or displaying accurate readings. Food safety may be at risk if the cooling system is not operating normally. It is best to verify that the refrigerator is actually maintaining proper temperatures and address the error promptly rather than continuing to use it in a degraded state.
Will resetting my LG refrigerator clear the E CO error?
A power reset, performed by unplugging the refrigerator for a few minutes and plugging it back in, may temporarily clear the error if it was triggered by a transient communication glitch. However, if the underlying cause is a loose connector, low voltage at CON101, or a failed transistor, the error will return. A reset is a reasonable first step but is not a substitute for proper diagnosis.
How much does it cost to repair the E CO error on an LG refrigerator?
Repair costs vary depending on the root cause. If only connector reseating is needed, the fix may cost nothing beyond a service call fee, which typically ranges from $75 to $150. If a display board replacement is required, parts and labor can range from $150 to $350 or more. Main PCB replacement tends to be the most expensive option, often falling in the $200 to $450 range depending on the model and labor rates in your area.

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