Daikin Air Conditioner Error Code UJ

The UJ code indicates a transmission error between the outdoor unit and the branch provider (BP) unit. The system was unable to receive valid communication data across that link for 10 continuous minutes and shut down as a result. This code is specific to multi-zone or VRV-type systems that use a BP unit for refrigerant and signal distribution. The most likely cause is a wiring issue between those two components.

A power reset may temporarily clear the UJ code, but if the underlying wiring or board fault is not resolved, the error will return within 10 minutes once the system attempts communication again. A reset alone is not a fix. The transmission path between the outdoor unit and BP unit must be inspected and the root cause corrected before the system will run reliably.

Repair costs vary depending on the cause. If the fix is simply reseating a loose wire or correcting a polarity error, labor costs alone may apply, typically in the range of $75 to $200 for a service call. If the transmission wire needs replacement, parts and labor could range from $150 to $400. A faulty control board in the outdoor unit or BP unit is the most expensive scenario, with parts and labor potentially ranging from $400 to $900 or more depending on the specific board required.

Start by turning off power to the entire system, then inspect the transmission wire running between the outdoor unit and the BP unit. Check that all terminal connections are tight, verify correct wiring polarity, and look for any visible damage along the wire run. If the wiring is intact and the error returns after restart, a technician should test the control boards in both units for communication circuit faults.

The system will typically stop operating when the UJ code is active, which prevents normal cooling or heating. Attempting to repeatedly restart the system without diagnosing the fault is not recommended, as underlying wiring issues could worsen over time. It is best to leave the system off until a technician can inspect the transmission wiring and connected components.