LG aircon CH40 error code & blinking light
Use this LG CH40 guide to decide when to stop resetting, what to capture, and what to check before parts are quoted. Match the model first; same-looking signals can point to different rows.
What does LG CH40 mean?
LG CH40 is listed as cT sensor error; thermistor is disconnected or shorted and current-transformer thermistor disconnected or shorted in Wall-Mounted Split rows such as HSV4 / HSV5 single-zone wall-mounted systems, LS091HSV / LS121HSV wall-mounted single-zone. The loaded row is source-backed by official diagnostic material. Do not collapse this code across model families; use the model, series, or system type to choose the right row. Confirm the exact model, series, or signal row before accepting a parts quote.
Open, shorted, displaced, or out-of-range thermistor or pressure-sensor reading.
Loose sensor connector, damaged sensor harness, or water-affected wiring.
PCB input fault after the sensor and wiring readings are confirmed.
What to do now
Use these steps before another reset, sensor check, or PCB quote.
Treat it as a fault signal
If CH40 returns or cooling is still abnormal, stop treating it as a simple reset issue.
Reset CH40 once
Capture the CH40 pattern first, then power-cycle once only and note whether the same fault returns.
Send these to us
CH40 error code and blinking light, a clear display photo and blinking-light video if the unit shows one, LG model stickers, affected rooms, reset result, and when the fault appears
Source-specific guidance
These diagnostic-reference notes help match the code to the exact model. Electrical, refrigerant, wiring, resistance, and component checks are technician work, not DIY steps.
| Source detail | What it says |
|---|---|
| Source repair action | Record CH40 and arrange outdoor current-sensor thermistor and PCB diagnosis. |
| Source repair action | Record the exact code and LED blink pattern before booking diagnosis. For LS091HSV / LS121HSV systems, this pattern points to: Current-transformer thermistor disconnected or shorted |
| Singapore / model note | Official LG HVAC HSV4 / HSV5 wall-mounted self-diagnosis table. Use this row only for matching single-zone wall-mounted systems. |
| Singapore / model note | Use this LS091HSV / LS121HSV LED table only when the installed model or service manual matches this standard wall-mounted single-zone family. |
What to check before repair
Use this split to separate safe evidence capture from the tests a technician should prove before quoting parts.
| You can check | Technician should confirm |
|---|---|
| Before resetting CH40, take a clear display photo and blinking-light video if the unit shows one. | Confirm which sensor CH40 maps to on the exact model table. |
| Capture the LG indoor and outdoor model stickers so the correct family row is used. | Measure the sensor value against the service-manual resistance or voltage range. |
| Note whether one room, several rooms, or the whole system is affected, plus whether it returns after one reset. | Check connector condition, harness continuity, and PCB input before replacing boards. |
What changes the next step
These clues decide whether the first check is room-side, shared outdoor-side, refrigerant-side, source-table, or model-family confirmation.
| What you see | What it points to |
|---|---|
| Only one indoor unit shows CH40. | The affected room, indoor board path, wiring route, or local component should be checked first. |
| Several rooms or the outdoor unit show the same CH40 fault. | The shared outdoor side, power path, communication trunk, or refrigerant circuit needs priority checking. |
| The fault appears immediately even before the unit cools properly. | Sensor value, connector, harness, and PCB input should be tested in that order. |
| The same code appears with different meanings in the source rows. | Model family, source table, and system type decide which meaning applies before parts are quoted. |
| The model belongs to Wall-Mounted Split rows such as HSV4 / HSV5 single-zone wall-mounted systems, LS091HSV / LS121HSV wall-mounted single-zone. | The loaded row is source-backed by official diagnostic material. Use the matching source row before quoting parts. |
Sensor or PCB decision
LG CH40 is usually repair-first if a sensor or harness reading is confirmed. Board replacement should wait until the sensor circuit is tested.
Sensor replacement is usually targeted when resistance or voltage readings are out of range.
Harness or connector damage can look like a sensor fault until continuity is checked.
PCB replacement is a later step if the sensor and wiring test correctly.
LG CH40 questions
What does the LG CH40 error mean?
Can I fix a LG CH40 error myself?
Is it safe to keep running the aircon with a CH40 error?
What causes a LG CH40 error?
Will a LG CH40 error need a repair or a full replacement?
What should I send a technician about a LG CH40 error?
Confirm the fault
Share the error code, model number and symptoms so we can assess the likely cause.
Not the right code?
Browse the full LG list or check a few codes in the same fault category.
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Read next
Use these if the quote mentions the parts, checks, or repair path this code points to.