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U9

U9 - Malfunction of transmission (other system) (Control System)

Daikin · Simple Self Diagnosis by Malfunction Code | Daikin

What does U9 mean?

This error code suggests a communication problem with an accessory device or another connected system.

Common Causes

  • Wiring fault with accessory
  • Accessory device malfunction
  • Incorrect system configuration

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Turn off the main power to the system.

  2. 2

    Check the wiring and connections for any accessory devices.

  3. 3

    Disconnect non-essential accessories to isolate the issue.

  4. 4

    Restore power and test.

  5. 5

    If the error persists, contact the system installer or technician.

Browse all codes in this manual (60)
Verified technical data. Last updated: April 2026

Related Faults

6-06-0 - External protection device activated (Heat reclaim ventilator)6-16-1 - Malfunction of PCB (Heat reclaim ventilator)6-26-2 - Ozone density abnormal (Heat reclaim ventilator)
Source: Simple Self Diagnosis by Malfunction Code | Daikin
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