LG Mini-Split CH05: Indoor/Outdoor Communication Error
On most LG systems, CH05 means the indoor and outdoor units have lost communication — a wiring, power, or control-board problem. Here's how to find which.
Last Updated: June 2026
CH05 on an LG mini-split most commonly flags a communication failure between the indoor and outdoor units — confirmed by LG's own support documentation. The two units constantly exchange a control signal; when that signal drops out, the system shuts down and displays CH05. The usual causes are unstable power, a wiring fault on the signal line, or a failed PCB. (LG code meanings can vary slightly by model line, so cross-check against your unit's manual if anything below doesn't match.)
Communication error between the indoor and outdoor units: the control signal that links the two has dropped or become unreliable. Common roots are power supply problems, signal-wire faults, and control-board failure.
Diagnosis steps
- Power-cycle both units correctly. Turn off the breakers for both the indoor and outdoor units, wait about 5 minutes, then switch both back on at the same time and retry. This clears a CH05 caused by a one-time power glitch. If it returns immediately, move on — it's a real fault.
- Check the power supply. A failed socket, tripped breaker, weak circuit, or blown fuse feeding either unit can cause CH05. Confirm both units actually have stable power, and that voltage at the outdoor unit holds under load — low or fluctuating voltage corrupts the communication signal.
- Inspect the signal wiring & order. The indoor/outdoor link uses a labeled terminal block (commonly 1, 2, 3 or L, N, S). Open both blocks and confirm: connections are tight (snug, not overtightened), no corrosion, no broken strands, and the wires land in the same order at both ends. A reversed or shifted wire — common after a DIY install or board swap — guarantees a communication fault.
- Check the wire run for damage. The communication wire usually runs alongside the refrigerant lines. Inspect where it enters/exits the building for chafed insulation, compression from over-tight clamps/staples, or rodent damage — any of which break the signal.
- Control board (PCB). If power and wiring are all good and CH05 persists, one of the control boards has failed. An LG technician can use diagnostic mode to identify whether the indoor or outdoor board is the source before replacement. LG PCBs are model-specific.
Parts & costs
| Part | Cost | Notes |
|---|---|---|
| 14/4 stranded comms cable | $30–80 | If the run is damaged. Match gauge to line length. |
| Digital multimeter | $20–50 | For the voltage and continuity checks above. |
| Control board (PCB) | $120–350 | Last resort. Verify exact model compatibility. |
Most CH05 fixes are wiring or power related — check those before buying a board. Commission earned on qualifying purchases.
Shop on Amazon →Frequently Asked Questions
Can I fix an LG CH05 myself?
Often yes. The most common fixes are a power reset (cut both breakers for 5 minutes, then restore together) and correcting the wiring between the indoor and outdoor units — a loose terminal, corrosion, or wires landed in the wrong order. If wiring and power are confirmed good and CH05 returns, the fault is a control board and needs a technician.
What's the difference between CH05 and CH38 on an LG?
They are not the same fault, so confirm the code on your display. CH05 is generally a communication error between the indoor and outdoor units (wiring/power/PCB). CH38 is generally tied to a low-refrigerant-pressure or unstable-power condition. Always cross-check the code against your unit's manual, as meanings can vary by model line.
Will resetting the breaker clear CH05?
It can clear a one-time fault caused by a power glitch. Turn off the breakers for both the indoor and outdoor units, wait about 5 minutes, then switch both on at the same time. If CH05 comes right back, you have a real wiring or board fault to diagnose, not just a stored error.