Daikin Error Code U4: Communication Error Indoor/Outdoor
Warning: Your Daikin HVAC system has a communication error between the indoor and outdoor units. It's safe to use, but you should schedule a professional repair soon.
How to Fix Daikin Code U4
- Check for any visible damage to the communication wire connecting your indoor and outdoor units. If you find any damage, do not attempt to repair it yourself.
- If the wire appears undamaged, the issue may be with the control board or refrigerant pressure sensor. These components require professional diagnosis and repair.
How to Reset Daikin Code U4
- Turn off the unit using the remote control or wall controller.
- Turn off the circuit breaker for the outdoor and indoor units. Wait 60 seconds.
- Restore power at the breaker.
- Turn the unit on with the remote control. If the error returns, the fault needs professional diagnosis.
What does U4 mean?
The Daikin U4 error code indicates a communication issue between your indoor and outdoor HVAC units. This could be due to a faulty communication wire, a problem with the control board, or an issue with the refrigerant pressure sensor. The system will continue to operate, but you may notice reduced performance or comfort.
Affected Models
Replacement Parts
| Part | OEM Number | Est. Cost |
|---|---|---|
| Communication Wire | — | — |
| Control Board | 44518C1601 | — |
| Refrigerant Pressure Sensor | 44518C1602 | — |
Related Codes on Same Models
| Code | Description | Severity |
|---|---|---|
| A1 | Indoor PCB Defective | Warning |
| A3 | Drain Level System Fault | Warning |
| A5 | Freeze-Up/Overheat Protection | Warning |
| A6 | Fan Motor Lock/Overcurrent | Warning |
| C4 | Heat Exchanger Thermistor Fault | Warning |
| C9 | Suction Air Thermistor Fault | Warning |
| E1 | Outdoor PCB Defective | Warning |
| E3 | High Pressure Switch Activated | Warning |
| E4 | Low Pressure Switch Activated | Warning |
| E5 | Compressor Motor Lock | Warning |