Daikin Air Conditioner Error Code U4

U4Daikin Air Conditioner

What this code means

Transmission error between indoor units and outdoor units - transmission not normal for extended time.

First step from the service manual

Check power supply voltage 208-230V; check for wrong wiring, loose terminal, or contact failure in transmission wiring.

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.

Start diagnosing U4 on your Daikin air conditioner

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What’s available for Daikin air conditioner models

Access Daikin air conditioner service manuals, wiring schematics, exploded parts views, and error code references on MyPros+.

Related Daikin air conditioner error codes

A0Error of external protection deviceA1Indoor unit PCB abnormalityA3Drain water level system abnormalityA5Freeze-up protection control or heating peak-cut control activated due to…A6Indoor unit fan motor abnormalityA7Swing flap motor abnormality/lockA8Abnormal power supply voltageA9Electronic expansion valve coil abnormalityAFHumidifier or related abnormalityAJCapacity setting abnormalityC1Transmission error between indoor unit PCB and fan PCB (FBQ only).C4Heat exchanger (liquid pipe) thermistor abnormalityC5Heat exchanger (gas pipe) thermistor abnormalityC6Combination error between indoor unit PCB and fan PCBC7Front panel open/close fault on CTXG series.C9Suction air thermistor abnormalityCCHumidity sensor system abnormalityCEPresence sensor or floor sensor abnormalityCJRoom temperature thermistor in remote controller abnormalityE1Outdoor unit PCB abnormalityE2Branch provider (BP) unit PCB abnormalityE3Actuation of high pressure switchE4Actuation of low pressure sensorE5Inverter compressor motor lockE7Outdoor unit fan motor abnormalityE9Electronic expansion valve coil abnormality (outdoor)F3Discharge pipe temperature abnormalityF6Refrigerant overchargedH3High pressure switch system abnormalityH7Outdoor unit fan motor signal abnormalityH9Outdoor air thermistor abnormalityJ0Branch provider (BP) liquid or gas pipe thermistor abnormalityJ3Discharge pipe thermistor abnormalityJ5Suction pipe thermistor abnormalityJ6Outdoor unit heat exchanger thermistor abnormalityJ7Outdoor liquid pipe thermistor (R7T) abnormalityJ9Subcooling heat exchanger gas pipe thermistor (R6T) abnormalityJAHigh pressure sensor abnormalityJCLow pressure sensor abnormalityL1Outdoor unit PCB abnormalityL4Radiation fin temperature riseL5Momentary overcurrent of inverter compressorL8Inverter current abnormalityL9Inverter startup errorLCTransmission error between control and inverter PCBP1High voltage of capacitor in main inverter circuitP4Radiation fin thermistor abnormalityU0Refrigerant shortageU2Power supply insufficient or instantaneous failureU3Check operation has not been conductedU5Transmission error between remote controller and indoor unitU8Transmission error between main and sub remote controllersU9Signal transmission error between indoor unit and outdoor unit in the same…UAExcessive number of indoor units or mismatching refrigerant type between indoor…UCAddress duplication of central remote controller.UETransmission error between centralized remote controller and indoor unit.UFSystem is not set yetUHSystem abnormality, refrigerant system address undefinedUJTransmission error between outdoor unit and branch provider (BP) unit
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