What does Daikin UJ mean?
Daikin UJ is listed as transmission fault with accessory device in Ceiling Cassette, Ceiling Suspended, Inverter Split rows such as General RA self-diagnosis guide, SkyAir. This meaning comes from the manufacturer's own diagnostic material. Confirm the exact model, series, or signal row before accepting a parts quote.
Loose, corroded, crossed, or damaged indoor-outdoor signal wiring.
Terminal block, connector, or junction fault on the indoor or outdoor side.
Indoor or outdoor PCB communication circuit fault after wiring is proven sound.
What to do now
Use these steps before customer action, a signal-wire check, or PCB quote.
Stop using the unit if UJ returns
If UJ remains displayed or returns during operation, do not attempt a reset the manufacturer does not list; arrange diagnosis.
No manufacturer reset steps listed for UJ
Capture the complete UJ display and model stickers first. The manufacturer lists no customer reset procedure; do not treat a generic power-cycle as manufacturer guidance.
Send these to us
UJ error code, a clear display photo, Daikin model stickers, affected rooms, operating state when the code appeared, and whether one room or every room failed
Guidance for your model
Notes that match the code to your exact model. Electrical, refrigerant, wiring, resistance and component checks are for a technician.
| Detail | What it says |
|---|---|
| Diagnostic note | Stop the system if it smells burnt, leaks, or trips power; note the exact model and code before booking diagnosis. |
| Singapore / model note | Official Daikin SM-TS3 row; use only where the relevant accessory device is installed. |
- Detail
- Diagnostic note
- What it says
- Stop the system if it smells burnt, leaks, or trips power; note the exact model and code before booking diagnosis.
- Detail
- Singapore / model note
- What it says
- Official Daikin SM-TS3 row; use only where the relevant accessory device is installed.
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 taking any system action on UJ, take a clear display photo. | Match UJ against your model family's listing before parts are quoted. |
| Capture the Daikin indoor and outdoor model stickers so the correct family row is used. | Test communication terminals, cable continuity, polarity, and outdoor power. |
| The manufacturer lists no customer reset procedure for this code. Note whether one room, several rooms, or the whole system is affected. | Read indoor and outdoor PCB indicators only after the signal path is proven sound. |
- You can check
- Before taking any system action on UJ, take a clear display photo.
- Technician should confirm
- Match UJ against your model family's listing before parts are quoted.
- You can check
- Capture the Daikin indoor and outdoor model stickers so the correct family row is used.
- Technician should confirm
- Test communication terminals, cable continuity, polarity, and outdoor power.
- You can check
- The manufacturer lists no customer reset procedure for this code. Note whether one room, several rooms, or the whole system is affected.
- Technician should confirm
- Read indoor and outdoor PCB indicators only after the signal path is proven sound.
What changes the next step
These clues decide whether the first check is room-side, shared outdoor-side, refrigerant-side, listed-meaning, or model-family confirmation.
| What you see | What it points to |
|---|---|
| Only one indoor unit shows UJ. | The affected room, indoor board path, wiring route, or local component should be checked first. |
| Several rooms or the outdoor unit show the same UJ fault. | Prioritise shared outdoor power, the communication trunk, terminal connections, and system controls. |
| The fault remains displayed or returns during operation. | Start with the checks the manufacturer lists for this code before approving parts. |
| The model family is different from the row you found online. | Use the model or series filter first; same-looking codes can still belong to different diagnostic tables. |
| The model belongs to Ceiling Cassette, Ceiling Suspended, Inverter Split rows such as General RA self-diagnosis guide, SkyAir. | This meaning comes from the manufacturer's own diagnostic material. Match the code to your model's listing before parts are quoted. |
- What you see
- Only one indoor unit shows UJ.
- What it points to
- The affected room, indoor board path, wiring route, or local component should be checked first.
- What you see
- Several rooms or the outdoor unit show the same UJ fault.
- What it points to
- Prioritise shared outdoor power, the communication trunk, terminal connections, and system controls.
- What you see
- The fault remains displayed or returns during operation.
- What it points to
- Start with the checks the manufacturer lists for this code before approving parts.
- What you see
- The model family is different from the row you found online.
- What it points to
- Use the model or series filter first; same-looking codes can still belong to different diagnostic tables.
- What you see
- The model belongs to Ceiling Cassette, Ceiling Suspended, Inverter Split rows such as General RA self-diagnosis guide, SkyAir.
- What it points to
- This meaning comes from the manufacturer's own diagnostic material. Match the code to your model's listing before parts are quoted.
Wiring or PCB decision
Daikin UJ should start with terminal, signal-cable, and power checks. PCB replacement only makes sense after the communication path is proven sound.
A loose terminal or bad junction is a targeted repair once the path is confirmed.
Signal-wire replacement depends mostly on access through trunking, ceiling, or concealed routes.
PCB cost should be weighed against age only after wiring and power checks pass.
Daikin UJ questions
What does the Daikin UJ error mean?
Can I fix a Daikin UJ error myself?
Is it safe to keep running the aircon with a UJ error?
What causes a Daikin UJ error?
Will a Daikin UJ error need a repair or a full replacement?
What should I send a technician about a Daikin UJ error?
Where to go next
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 Daikin list or check a few codes in the same fault category.
Read next
Use these if the quote mentions the parts, checks, or repair path this code points to.