Daikin U5

What does Daikin U5 mean?

The U5 code means the indoor unit has lost communication with the wired remote controller. Daikin remote controllers talk to the indoor PCB over a two-wire P1/P2 low-voltage bus, and when the indoor board times out waiting for a response from the controller — or vice versa — U5 is raised. Controller wiring faults, bus-address conflicts on group-controlled setups, and a failed controller itself are the common roots.

Symptoms

• Remote controller displays U5 and will not respond to buttons
• Indoor unit stops or refuses to start
• Controller screen blank or garbled
• Multiple controllers on a group bus showing the fault
• Power-cycle clears the fault briefly, then U5 returns

Common causes

• Broken, shorted, or miswired P1/P2 controller cable
• Loose P1/P2 terminal at the controller or indoor PCB
• Remote-controller board failure
• Incorrect master/slave setting with two controllers on one group
• Defective indoor unit PCB communication port

Diagnostic steps

1. 01

   Power-cycle the indoor unit

   Isolate the indoor disconnect for at least 30 seconds and restore. Many U5 events are one-off lock-ups.

2. 02

   Inspect P1/P2 terminations

   Open the controller backplate and the indoor terminal cover. Confirm P1 and P2 land on the correct screws and are torqued tight.

3. 03

   Continuity-test the controller cable

   Disconnect one end, meter each conductor end to end, and check for shorts between conductors or to ground.

4. 04

   Verify controller addressing

   On systems with two controllers sharing one indoor unit, confirm one is set master and the other slave per the installation manual.

5. 05

   Swap controllers

   If a known-good controller is available, swap it in place. If the fault clears, the original controller is faulty.

6. 06

   Replace indoor PCB

   If wiring and controller both check out, the indoor PCB communication port is faulty — swap the indoor PCB and reconfigure settings.

When to call a professional

Call a licensed technician if swapping controllers and verifying wiring does not clear U5. On group-controlled and centralised-controller systems, bus topology, terminator settings, and controller addressing must match the design — wrong settings produce U5 even on sound hardware. A Daikin-trained tech can read the indoor PCB diagnostic indicators to localise the fault without guesswork, and will verify the full control bus on commissioning after any PCB or controller replacement.