1. It is judged an error whenever the outdoor unit receives the signal O2 Alarm Generated from the indoor unit.
2. With the indoor unit´s EEPROM setting (item code 0B) set to 0001, the EXCT input was shorted.

Check and
Correction

1. System configuration
      1-1 Is an O2 sensor being used?
      If Yes, see 3-1.
      If No, see 2-1.
    
2. 2-1 Indoor EEPROM setting
      Is the EEPROM setting, item code 0B, on the indoor control board set to 0001?
      If Yes, see 3-1 after modification.
      If No, see 4-1.
    
3. 3-1 EXCT wiring
      Is the EXCTsocket (wire) shorted?
      If Yes, Modify the wiring.
      If No, see 4-1.
                                                     
4. Indoor control board
      4-1 Is the alarm triggered if the EXCT socket (wire) is disconnected, and the power is reset?
      If Yes, see 4-3.
      If No, see 4-2.
   
      4-2 Since there is no error, see what happens.
   
      4-3 Indoor control board defective → replace board