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Error code reference

LG Freezer Error Code CO/--

Improper communication between MAIN PCB and display PCB (no communication for 30 consecutive seconds due to…

LG codesLG freezer codes

Improper communication between MAIN PCB and display PCB (no communication for 30 consecutive seconds due to connector unplugged or defected TR in communication part).

First step from the service manual

Check display PWB lead wire for cut wire or PWB malfunction; replace Case display.

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

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What CO/-- means on a LG freezer

The CO/-- error code on an LG freezer indicates a communication failure between the main PCB (printed circuit board) and the display PCB. Specifically, the control system has detected an absence of communication signal between these two boards for 30 or more consecutive seconds. These two boards rely on a continuous data exchange to coordinate temperature control, user input processing, and status display. When that signal is interrupted or lost entirely, the unit flags the CO/-- code to alert the technician that the communication link has broken down.

The two most common root causes are a physically disconnected or damaged wiring harness connector between the boards, or a failed transistor (TR) in the communication circuit of one of the PCBs. Connectors can work loose over time due to vibration, or they may have never been fully seated after a previous repair. A cut or pinched lead wire in the display PWB wiring harness can also sever the signal path completely. These wiring issues are typically the first thing to inspect, as they are more common and easier to address than a failed transistor on the board itself.

If the wiring and connectors check out as intact and properly seated, the fault likely resides in a defective transistor within the communication circuitry on either the main PCB or the display PCB. This type of component-level failure means the board is unable to send or receive the communication signal even when the physical connections are good. In this scenario, replacing the case display assembly or the main PCB is the appropriate corrective action.

Source: manufacturer service documentation.

Common causes of CO/--

  1. 01

    Disconnected or loose wiring harness connector

    Wiring / connection

    The connector linking the display PWB to the main PCB may have come unplugged or is not fully seated. Inspect the connector at both ends of the harness for any looseness or signs of it having pulled free.

  2. 02

    Cut or damaged display PWB lead wire

    Part replacement

    The lead wire running to the display PWB can become pinched, cut, or broken, interrupting the communication signal entirely. Visually trace the wire along its full length and flex it gently to check for hidden breaks.

  3. 03

    Defective display PCB (case display assembly)

    Part replacement

    A failed transistor in the communication circuit of the display PCB can prevent the board from sending or receiving data signals. If wiring checks out, replacing the case display assembly is the recommended next step.

  4. 04

    Defective main PCB

    Part replacement

    A faulty transistor or communication circuit failure on the main PCB can also cause this error even when all wiring is intact. This is typically diagnosed after ruling out the display PCB and wiring as the source of the fault.

See the test procedure for each cause

Frequently asked questions about CO/--

What does CO/-- mean on a LG freezer?
The CO/-- code means the main PCB and the display PCB have lost communication for 30 or more consecutive seconds. This can happen because a connector in the wiring harness has come unplugged, a lead wire has been cut or damaged, or a transistor in the communication circuit on one of the boards has failed. The freezer will display this code until the communication link is restored.
Can I fix the CO/-- error myself on my LG freezer?
A knowledgeable DIYer can start by inspecting the wiring harness and connectors between the display PWB and the main PCB. If a connector is simply loose or unplugged, reseating it may resolve the error without any parts. If a wire is cut or a board is faulty, replacing the case display assembly or main PCB is required, which is a more involved repair.
Is it safe to keep using my LG freezer when the CO/-- code is showing?
A CO/-- error means the display and main control board are not communicating, which can impair the freezer's ability to properly regulate and display temperature. It is not recommended to rely on the appliance for long-term food storage while this error is active. Address the fault promptly to avoid potential food spoilage.
Will resetting my LG freezer clear the CO/-- error code?
A power reset may temporarily clear the code if the fault was caused by a momentary signal disruption, but it will return if the underlying cause is still present. If a connector is loose, a wire is damaged, or a PCB component has failed, the error will reappear until the physical issue is repaired. A reset alone is not a fix for this error.
How much does it cost to repair a CO/-- error on an LG freezer?
If the fix is simply reseating a connector, there may be no parts cost and minimal labor cost. Replacing a display PCB or case display assembly typically costs anywhere from $80 to $250 or more for the part, plus labor if you use a technician. Replacing the main PCB can range from $150 to $400 or more depending on the model and parts availability.

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