Skip to main contentStart diagnosing 51 on your LG air conditioner→
What this code means
Indoor connection over capacity — total connected indoor unit capacity exceeds outdoor unit rated capacity (130% for 10HP, 115% for 4.5HP, 120% for 6HP).
First step from the service manual
Verify if total capacity of connected indoor units is within rated capacity of outdoor unit.
Next steps: diagnose the root cause
1
Verify the error code is active
Power cycle the unit and see if the code returns. If it does, the fault is persistent and requires diagnosis.
2
Get the full diagnostic procedure
Get step-by-step guidance, test values, and wiring diagrams from the OEM service manual.
$29/month · Cancel anytime · Or $9.95 3-day pass
What’s available for LG air conditioner models
Access LG air conditioner service manuals, wiring schematics, exploded parts views, and error code references on MyPros+.
Related LG air conditioner error codes
01Indoor room thermistor error (open/short circuit, poor solder, or internal…02Indoor inlet pipe thermistor error (open/short circuit, poor solder, or…03Communication error between wired remote controller and indoor unit04Drain pump malfunction05Communication error between outdoor unit and indoor unit06Indoor outlet pipe thermistor error (open/short circuit, poor solder, or…07Operation mode between indoor unit and outdoor unit is different09Indoor unit EEPROM error1Indoor suction temperature thermistor or indoor pipe temperature thermistor is…10Poor indoor fan motor operation; disconnected fan motor connector or indoor fan…100System off due to excessive increase of discharge temperature of constant speed…101System off due to excessive increase of discharge temperature of constant speed…102Discharge temperature of Sub2 outdoor unit No.1 constant speed compressor103Discharge temperature of Sub2 outdoor unit No.2 constant speed compressor104Communication error between main outdoor unit and sub1 outdoor unit105Transmission error between fan PCB and inverter PCB106Outdoor unit fan PCB IPM failure107Low voltage of main outdoor fan motor driver108Communication error of main outdoor unit fan motor109Excessive rise of high pressure in sub1 outdoor unit11Outdoor unit cannot recognize the indoor unit; addressing signal does not come…110Reverse connection of R, S, T power line of Sub1 outdoor unit (misconnection or…111Communication error from main outdoor unit to sub1 outdoor unit113Outdoor unit liquid pipe (condenser) temperature sensor error114Outdoor unit sub-cooling inlet/outlet temperature sensor error115Outdoor unit subcooling outlet temperature sensor error116High pressure sensor of sub1 outdoor unit is open or short.117Low pressure sensor of sub1 outdoor unit is open or short.118Air temperature sensor of sub1 outdoor unit is open or short.12Misconnection of connecting cables between indoor and outdoor units, or…120Compressor suction pipe temperature sensor of sub1 outdoor unit is open or…121Discharge temperature sensor of constant speed compressor 1 of sub1 outdoor…122Discharge temperature sensor of constant speed compressor 2 of sub1 outdoor…123Temperature sensor of front-side heat exchanger (A) of sub1 outdoor unit is…124Temperature sensor of rear-side heat exchanger (B) of sub1 outdoor unit is open…125Liquid pipe (condenser) temperature sensor of sub1 outdoor unit is open or…126Sub1 outdoor unit excessive cooling inlet temperature sensor open or short.127Sub1 outdoor unit excessive cooling outlet temperature sensor open or short.128Sub2 outdoor unit high pressure sensor open or short (3 units).129Sub2 outdoor unit low pressure sensor open or short (3 units).13PSC error130Sub2 outdoor unit air temperature sensor open or short (3 units).132Compressor suction temperature sensor of sub2 outdoor unit is open or short.133Sub2 outdoor unit constant speed compressor 1 discharge temperature sensor open…134Sub2 outdoor unit constant speed compressor 2 discharge temperature sensor open…135Temperature sensor of front-side heat exchanger (A) of sub2 outdoor unit is…136Temperature sensor of rear-side heat exchanger (B) of sub2 outdoor unit is open…137Outdoor unit liquid pipe (condenser) temperature sensor of sub2 unit is open or…138Sub2 outdoor unit excessive cooling inlet temperature sensor open or short (3…139Sub2 outdoor unit excessive cooling outlet temperature sensor open or short (3…14Compressor phase current error (180 driver compressor control model only).140Excessive rise of high pressure in sub2 outdoor unit141Wrong connection of 3 phase power cable of sub2 outdoor unit (reverse phase or…142Communication error between outdoor units143Excessive rise in high pressure of sub1 outdoor unit144Excessive drop in low pressure of sub1 outdoor unit145High pressure rise of Sub2 outdoor unit146Low pressure drop of Sub2 outdoor unit147Short voltage or excess voltage of Sub1 outdoor unit148Voltage detection circuit of sub1 outdoor unit is out of order.149Short voltage/excess voltage of Sub2 outdoor unit15Incorrect wiring of compressor phases (U, V, W).150Outdoor voltage sensor of Sub2 outdoor unit open or short (3 units).151Outdoor 4-way (reversing valve) switching error; pressure change does not occur…152System off due to excessive increase of discharge temperature of constant speed…153System off due to excessive increase of discharge temperature of constant speed…154Excessive rise of high pressure in sub3 outdoor unit155Wrong connection of 3 phase power cable of sub3 outdoor unit (reverse phase or…156Transmission error between outdoor units157High pressure sensor of sub3 outdoor unit is open or short.158Low pressure sensor of sub3 outdoor unit is open or short.159Air temperature sensor of sub3 outdoor unit is open or short.161Compressor suction temperature sensor of sub3 outdoor unit is open or short.162Discharge temperature sensor of constant speed compressor 1 of sub3 outdoor…163Discharge temperature sensor of constant speed compressor 2 of sub3 outdoor…164Temperature sensor of front-side heat exchanger (A) of sub3 outdoor unit is…165Temperature sensor of rear-side heat exchanger (B) of sub3 outdoor unit is open…166Liquid pipe (condenser) temperature sensor of sub3 outdoor unit is open or…167Subcooling inlet temperature sensor of sub3 outdoor unit is open or short.168Subcooling outlet temperature sensor of sub3 outdoor unit is open or short.169Excessive rise in high pressure of sub3 outdoor unit170Excessive drop in low pressure of sub3 outdoor unit171Input voltage of sub3 outdoor unit exceeds tolerable range (3phase 380V±10% or…172Outdoor voltage sensing error of sub3173Failure of main constant speed compressor operation174Failure of Sub1 constant speed compressor 1 operation175Failure of Sub1 constant speed compressor 2 operation176Failure of Sub2 constant speed compressor 1 operation177Failure of Sub2 constant speed compressor 2 operation178Failure of Sub3 constant speed compressor 1 operation179Failure of Sub3 constant speed compressor 2 operation193Fan PCB heatsink temperature high194Fan PCB heatsink temperature sensor error2Outdoor suction temperature thermistor or outdoor pipe temperature thermistor…200Pipe detection error201HR unit liquid pipe temperature sensor error202HR unit sub-cooling inlet pipe temperature sensor error203HR unit sub-cooling outlet pipe temperature sensor error204Transmission error between HR unit and outdoor unit205HR unit 2 liquid pipe temperature sensor error (open or short).206HR unit 2 sub-cooling inlet pipe temperature sensor error (open or short).207HR unit 2 sub-cooling discharge pipe temperature sensor error (open or short).208Transmission error between HR unit 2 and outdoor unit.209HR unit 3 liquid pipe temperature sensor error (open or short).21DC peak / IPM fault210HR unit 3 sub-cooling inlet pipe temperature sensor error (open or short).211HR unit 3 sub-cooling discharge pipe temperature sensor error (open or short).212Transmission error between HR unit 3 and outdoor unit.213HR unit 4 liquid pipe temperature sensor error (open or short).214HR unit 4 sub-cooling inlet pipe temperature sensor error (open or short).215HR unit 4 sub-cooling discharge pipe temperature sensor error (open or short).216Transmission error between HR unit 4 and outdoor unit.217HR unit 5 liquid pipe temperature sensor error (open or short).218HR unit 5 sub-cooling inlet pipe temperature sensor error (open or short).219HR unit 5 sub-cooling discharge pipe temperature sensor error (open or short).22Overcurrent flows to inverter compressor; CT sensing circuit detects current…220Transmission error between HR unit 5 and outdoor unit.221HR unit 6 liquid pipe temperature sensor error (open or short).222HR unit 6 sub-cooling inlet pipe temperature sensor error (open or short).223HR unit 6 sub-cooling discharge pipe temperature sensor error (open or short).224Transmission error between HR unit 6 and outdoor unit.225HR unit 7 liquid pipe temperature sensor error (open or short).226HR unit 7 sub-cooling inlet pipe temperature sensor error (open or short).227HR unit 7 sub-cooling discharge pipe temperature sensor error (open or short).228Transmission error between HR unit 7 and outdoor unit.229HR unit 8 liquid pipe temperature sensor error (open or short).23DC voltage charging failure for inverter compressor driving230HR unit 8 sub-cooling inlet pipe temperature sensor error (open or short).231HR unit 8 sub-cooling discharge pipe temperature sensor error (open or short).232Transmission error between HR unit 8 and outdoor unit.24Excessive rise of discharge pressure in main outdoor compressor240Central controller connector error (CNU connection failure)241Central controller data transmission error (sending error)242Central controller receive error243Central controller receive buffer overflow244Central controller receive timeout245Central controller send timeout246Central controller receive timeout25Input voltage high/low error250Central controller check sum error251Central controller receive zero error252Central controller wrong address error26DC Compressor Position Error27PFC Fault28DC Link high voltage (1ph29Inverter compressor over current3Abnormal operation of multi product; resetting of remote control due to…32Discharge temperature of inverter compressor at main outdoor unit is…33Discharge temperature of constant speed compressor at main outdoor unit is…34Over-increase of discharge pressure of compressor35Low pressure of main outdoor unit; system off by excessive decrease of low…39Transmission error between PFC Micom and INV Micom on outdoor inverter PCB.4Temperature of heat sink (power module) has exceeded 95°C, causing overheating…40Inverter compressor CT sensor fault41Inverter compressor discharge pipe temperature sensor fault42Low pressure sensor error43High pressure sensor error44Outdoor unit air temperature sensor error (sensor measured value not normal…45Heat exchanger temperature sensor (A) fault in outdoor unit46Outdoor unit compressor suction temperature sensor fault47Constant speed compressor discharge pipe temperature sensor fault48Heat exchanger temperature sensor (B) fault in outdoor unit49Outdoor voltage sensing error5Abnormal operation of multi product due to simultaneous cooling and heating…50Outdoor unit 3-phase power omission error52Transmission error from inverter PCB to main PCB in outdoor unit53Transmission error from indoor unit to main PCB in outdoor unit54Reverse connection or omitting connection of R, S, T power of main outdoor unit…55Transmission error from central controller to main PCB in outdoor unit56Transmission error from main PCB in outdoor unit to central controller57Transmission error from main PCB to inverter PCB in outdoor unit59Slave outdoor unit mixed installation6DC peak current error60Outdoor unit EEPROM check sum error61Outdoor pipe temperature (condensation temperature) exceeded 58°C or 60°C in…62Overheat of inverter PCB heat sink63Condenser pipe low temperature error on outdoor unit.65Heat sink thermistor error (open/short)67Outdoor BLDC fan lock error7Running current overload (CT2)70Constant speed compressor CT sensor error71Inverter input current (PFC) CT sensor error73PFC fault error (software)743-phase power unbalance75Fan CT sensor error76Fan DC link high voltage error77Fan over current error78Fan motor hall sensor error79Fan starting failure error8Indoor fan lock error (BLDC fan model only)86Main PCB EEPROM error87Fan PCB EEPROM error9Outdoor fan lock error (BLDC fan model only)C1Indoor temperature sensor (thermistor) is short or open circuit.C2Outdoor temperature sensor (thermistor) is short or open circuit.C4Heat sink sensor errorC5Communication error (serial communication) between indoor and outdoor units.C6DC peak current errorC7Over current error (CT2)C8Indoor fan is locked (BLDC fan model only).C9Outdoor fan is locked (BLDC fan model only).CADischarge pipe thermistor (D-Pipe TH) is short or open.CBEEPROM errorCCPSC errorCDCompressor phase current error (180 driver comp control model only).CH00No error present.CH01Indoor air sensor error (connector connection error, faulty PCB, or faulty…CH02Indoor inlet pipe sensor error (connector connection error, faulty PCB, or…CH03Communication error between wired remote controller and indoor unit (connector…CH04Drain pump or float switch error (float switch open or water overflow…CH05Communication error between indoor PCB and outdoor PCB.CH06Open or short circuit of outlet pipe sensor (indoor).CH07Different mode operation errorCH08Indoor unit expansion valve malfunction.CH09Indoor unit EEPROM error (EEPROM checksum discordance or EEPROM data read…CH10Indoor unit BLDC motor fan lock (faulty motor operation).CH12Indoor unit middle pipe sensor open/short error.CH15Communication error between indoor PCB and fan board.CH16Fire alarm triggered.CH21DC Peak (IPM Fault)CH22CT 2 (Max CT)CH23DC Link Low VoltageCH24High pressure switch operatedCH25Low voltage or overvoltage condition detected.CH26DC compressor position error (compressor wiring connection error).CH27PSC Fault ErrorCH28DC Link High VoltageCH29Compressor phase over-current.CH31CT error (low current detected).CH32High temperature in discharge pipe of the inverter compressor.CH33Discharge pipe temperature too high (constant speed compressor).CH34High pressure sensor reading is high.CH35Low pressure sensor reading is low.CH36Refrigerant leak / loss detected.CH37Exceed the compression ratio limit.CH38Refrigerant leakage detection (alternate code for CH36).CH40CT sensor open or short circuitCH41Inverter discharge pipe thermistor open or short circuit.CH42Low pressure sensor open or short circuit.CH43High pressure sensor open or short circuit.CH44Outdoor air temperature thermistor open or short circuit.CH45Condenser pipe temperature sensor error (open/short)CH46Suction pipe temperature sensor error (open/short)CH47Constant-speed discharge pipe thermistor open or short circuit.CH48Condenser pipe temperature sensor error (open/short)CH49Voltage sensor open or short circuit.CH51Excess capacityCH52Communication error between inverter board and main board.CH53Communication error between outdoor unit and indoor unit.CH54Phase error on outdoor unitCH55Communication error (outdoor unit receiving from central controller).CH56Communication error (outdoor unit sending to central controller).CH60EEPROM checksum errorCH61Condenser pipe temperature too high.CH62High temperature in outdoor PCBA heat sink.CH63Condenser pipe temperature too low.CH64Momentary power interruption detected.CH65Heatsink thermistor open or short circuit.CH67Outdoor BLDC motor fan lock (faulty motor operation).CH72Detect 4-way valve transfer failure.CH93Communication error between indoor and outdoor units (alternate code).CLChild lock is active; all keys on wired remote are locked.E1Indoor pipe thermostat short or open circuit.E101Indoor unit communication errorE102Communication error between indoor unit and outdoor unit, displayed on indoor…E108Error due to repeated address setting when 2 or more devices have the same…E109Communication address not confirmed for outdoor unit.E121Error on indoor room temperature sensor of indoor unit (Short or Open).E122Indoor unit heat exchanger in temperature sensor error (open or short).E123Indoor unit heat exchanger out temperature sensor error (open or short).E126Discharge sensor error (Short or Open) on indoor unit.E128Try-run mode self-diagnostic error (evaporator pipe in sensor related).E129EVA OUT temperature sensor of indoor unit is detached from EVA OUT pipe.E130Heat exchanger in/out sensors of indoor unit are both detached simultaneously.E135Electronic Expansion Valve opening malfunction (2nd stage)E149Error due to AHU master indoor unit sensor setting.E151Error due to opened EEV of indoor unit (2nd detection)E152Error due to closed EEV of indoor unit (2nd detection)E153Detection of floating switch of indoor unit's drain pump (2nd detection)E154Indoor unit fan motor error (below 450RPM for 15 minutes).E161Mixed operation mode errorE162EEPROM error of MICOME163Indoor unit's remote controller option input is incorrect or missing; outdoor…E164Error due to incompatible indoor unit model or Fahrenheit/Celsius confusion.E180Simultaneous opening of cooling/heating MCU SOL valve (1st detection).E181Simultaneous opening of cooling/heating MCU SOL valve (2nd detection).E185Cross wiring error between communication and power cable of indoor unit.E186Connection error or problem on SPI feedback.E190No temperature changes in EVA IN during pipe inspection or changes in…E191No temperature changes in EVA OUT during pipe inspection or changes in…E198Error due to disconnected thermal fuse of indoor unit (Open).E199No pipe check operation performed after installation through auto addressing…E2Indoor air thermostat short or open circuit.E201Communication error between indoor and outdoor unitsE202Communication error between indoor and outdoor unitsE2031 minute time out of communication error between Main PCB and Inverter PCB.E205Communication error on all PBA within the outdoor unit C-Box, communication…E206Internal PCB communication error of outdoor unit C-BoxE211MCU branch part setup errorE212MCU branch part setup errorE213Indoor unit assigned on MCU is not installed even though total count matches.E214Setup error for MCU quantity usedE215MCU branch part setup errorE216MCU branch part setup errorE217MCU branch part setup errorE218MCU branch part setup errorE219MCU branch part setup errorE220More actual indoor unit connections than number of indoor units assigned to MCU.E221Outside temperature sensor error (short/open)E224Error on water temperature sensor of main outdoor unit (Short or Open).E225Error on control box temperature sensor of main outdoor unit (Short or Open).E231Error on COND OUT temperature sensor of main outdoor unit (Short or Open).E237Condenser out sensor error (short/open)E241COND OUT sensor is detached from sensor holder on pipe.E246Try-run mode self-diagnostic error.E251Condenser temperature sensor error (short/open)E257Error on discharge temperature sensor of compressor 2 (Short or Open).E261Try-run mode self-diagnostic error.E262Discharge temperature sensor of compressor 1 is detached from the sensor holder…E263Discharge temperature sensor of compressor 2 is detached from the sensor holder…E265Dislocation error of compressor SUMP temperature (oil temperature) sensor.E266Top sensor of compressor 1 is detached.E267Top sensor of compressor 2 is detached.E269Suction temperature sensor is detached from the sensor holder on the pipe.E276Error on top sensor of compressor 1 (Short or Open).E277Error on top sensor of compressor 2 (Short or Open).E291Refrigerant leakage or error on high pressure sensor (Short or Open).E296Refrigerant leakage or error on low pressure sensor (Short or Open).E3Pipe temperature and room temperature are too close together.E301High pressure sensor is detached.E306Low pressure sensor is detached.E308Error on suction temperature sensor (Short or Open).E311Error on temperature sensor of double layer pipe/liquid pipe (sub heat…E320Compressor OLP sensor error (short/open)E321Error on EVI (ESC) IN temperature sensor (Short or Open).E322Error on EVI (ESC) OUT temperature sensor (Short or Open).E323Error on suction sensor 2 (Short or Open).E346Error due to operation failure of outdoor Fan2.E347Motor wire of outdoor Fan2 is not connected.E348Lock error on Fan2 of outdoor unit.E353Error due to overheated motor of outdoor unit's Fan2.E355Error due to overheated IPM of Fan2 (IPM internal temperature more than 85°C).E361Error due to operation failure of inverter compressor 2.E364Error due to over-current of inverter compressor 2.E365V-limit error of inverter compressor 2.E366Error due to over voltage/low voltage of inverter PBA2.E367Error due to unconnected wire of compressor 2.E368Output current sensor error of inverter PBA2.E369DC voltage sensor error of inverter PBA2.E371Error due to the INV2 Data Flash.E374Heat sink temperature sensor error of inverter PBA2.E378Error due to overcurrent of outdoor Fan2.E383Error due to over current of Fan2.E385Error due to input current of inverter 2.E386Over-voltage/low-voltage error of outdoor Fan2 PCB.E387Hall IC connection error of outdoor Fan2.E389V-limit error on Fan2 of compressor.E391Error due to the Fan2 DataFlash.E393Output current sensor error of outdoor Fan2 PCB.E396DC voltage sensor error of outdoor Fan2 PCB.E399Heat sink temperature sensor error of outdoor Fan2 PCB.E4Product running above 10 minutes and pipe temperature below 2 degrees.E400Error due to overheat caused by contact failure on IPM of Inverter PBA2 (IGBT…E401Outdoor unit freezing (compressor stop)E403Freezing control causes compressor downE404Outdoor unit overloadE407Compressor operation stop due to high pressure protection controlE410Compressor operation stop due to low pressure protection control or refrigerant…E413Sump sensor error due to protection controlE416Compressor operation stop due to discharge temperature/top temperature sensor…E419Try-run mode self-diagnostic error.E422EEV or Valve Close errorE425Phase reversal or phase failure on 3-phase outdoor unit wiring (R-S-T-N)…E428Compressor operation stop due to abnormal compression ratioE435Flow Switch Error.E436Error on heat exchanger frost protection.E438EVI (ESC) EEV leakage or internal leakage of intercooler or incorrect connector…E439Refrigerant leakage errorE440High temperature (over 30°C) of outdoor in heating modeE441Cooling operation is not available since the outdoor air temperature is lower…E442Refrigerant charging restriction in heating mode when air temperature is over…E443Operation prohibited due to low pressureE445CCH malfunction and sump sensor miswiring errorE446Error due to operation failure of outdoor Fan1.E447Motor wire of outdoor Fan1 is not connected.E448Lock error on outdoor Fan1.E450Abnormally high temperature on condenser (2nd detection).E451Low pressure switch (2nd detection).E452Error due to ZPC detection circuit problem or power failure (momentary…E453Error due to overheated motor of outdoor unit's Fan1.E454Error due to the outdoor unit fan RPM.E455Error due to overheated IPM of Fan1E457Outdoor unit reversed direction of the wind error.E458Compressor excess current errorE461Error due to operation failure of inverter compressor 1.E462Primary current over trip error / current protection control causes compressor…E463OLP protection control caused compressor downE464Error due to over-current of inverter compressor 1.E465V-limit error of inverter compressor 1.E466Error due to over voltage/low voltage of inverter PBA1.E467Error due to unconnected wire of compressor 1.E468Output current sensor error of inverter PBA1.E469DC voltage sensor error of inverter PBA1.E470Outdoor EEPROM error (checksum).E471Error due to the INV1 Data Flash.E474Heat sink temperature sensor error of inverter PBA1.E475Outdoor unit BLDC Fan 2 error.E478Error due to overcurrent of outdoor Fan1.E483Error due to over current of Fan1.E484PFC overload error.E485Error due to input current of inverter 1.E486Error due to over voltage/low voltage of outdoor Fan PCB.E487Hall IC error of outdoor Fan1E489V-limit error on Fan1 of compressor.E491Error due to the Fan1 DataFlash.E493Output current sensor error of outdoor Fan1 PCB.E496DC voltage sensor error of outdoor Fan1 PCB.E499Heat sink temperature sensor error of outdoor Fan1 PCB.E500Error due to overheat caused by contact failure on IPM of Inverter PBA1E503Error due to alert the user to check if the service valve is closed.E504Error due to self diagnosis of compressor operation.E505Error due to self diagnosis of high pressure sensor.E506Error due to self diagnosis of low pressure sensor.E508Error due to not using Smart Install.E515Error due to overheat of control box.E516Error due to no feedback from the fan of the control box.E552Compressor down due to low discharge pressure.E554Gas leak errorE556Capacity mismatch between indoor and outdoor units.E557Option code mismatch among the indoor units (only for DPM).E559Indoor operation stop due to unconfirmed error on outdoor unit.E560Outdoor unit's option switch setting error (when inappropriate option switch is…E563Error due to module installation of indoor unit with old software versionE573Error due to using single type outdoor unit in a module installation.E590Outdoor EEPROM checksum error between MAIN and INVERTER.E702Error due to closed EEV of indoor unit (1st detection).E703Error due to opened EEV of indoor unit (1st detection).FLWater full indicator display code.P2Water full condition detected for 10 seconds.UPTrial operation (commissioning) not completed
STOP GUESSING·Start verifying
Start diagnosing faster today.
$29/month · Cancel anytime · Or $9.95 3-day pass
Get Started