LG Mini-Split Code CH40
Hard lockoutShown as: Outdoor LED01 (red) blinks 4 times, LED02 (green) does not blink
Current transformer (CT) sensor error - the current-sensing circuit on the outdoor board is open or shorted.
Manual wording: “CT Sensor Error; Thermistor is disconnected or has shorted out”
Documented for: All LG residential mini-split outdoor units
Likely causes, most common first
- PCB current-sensing circuit part burned out
When to call a technician
The service manual states that because CH40 is caused by burned-out components on the outdoor PCB, the board is replaced without separate inspection. Technician only.
A LG mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- MULTI F / MULTI F MAX Outdoor Unit Installation Manual (LG Electronics U.S.A., Inc., Multi F and Multi F MAX multi-zone heat pump outdoor units (LMU series) with standard wall-mount, Art Cool, cassette and ducted indoor units) · checked 2026-08-25
- Defining Common Error Codes - Standard Wall-Mounted High-Efficiency Single Zone Systems (LG Electronics U.S.A. - Commercial Air Conditioning, LS091HSV and LS121HSV systems (LSN091HSV / LSN121HSV indoor units, LSU091HSV / LSU121HSV outdoor units)) · checked 2026-08-25
- Room Air Conditioner SVC Manual (General) - Trouble Shooting Guide with Error Code (LG Electronics, All LG single-zone room air conditioner / mini-split chassis (SW, SB, SC, S4, S5, SH, SA, SJ, SK)) · checked 2026-08-25