This list of Mitsubishi Air Conditioning fault codes will give you an idea of what is wrong with your Air Conditioning system.

Mitsubishi Air Conditioning Error codes:
P1    Intake sensor error
P2    P9 Pipe sensor error
E6    E7 Indoor/outdoor unit communication error
P4    Drain sensor error
P5    Drain pump error
PA    Forced compressor error
p6    Freezing/Overheating safeguard operation
EE    Communication error between outdoor and indoor units
P8    Pipe temperature error

E4    Remote controller signal receiving error

Fb    Indoor unit control system error

E0    E3 Remote controller transmission error

E1    E2 Remote controller control board error

Troubleshooting an LED display on an outdoor controller board

E9    Indoor/outdoor unit communication error (Transmitting error) (Outdoor unit)
U3, U4    Open/short of outdoor unit thermistors
UF    Compressor overcurrent interruption (When compressor locked)
U2    Abnormal high discharging temperature/49C worked/insufficient refrigerant
U1, Ud -Abnormal High Pressure /Overheat
U5    Abnormal temperature of a heat sink
U8    Outdoor unit fan safeguard stop
U6    Compressor overcurrent interruption/Abnormality of a power module.
E6 – Indoor/outdoor unit transmission error (signal receiving error).
E7 – Indoor/outdoor unit transmission error (transmitting error).
E8 – Indoor/outdoor unit transmission error (signal receiving error).
E9 – Indoor/outdoor unit transmission error (transmitting error).
E0 – Remote control transmission error (signal receiving error)
E3 – Remote control transmission error (transmitting error)
E4 – Remote control transmission error (signal receiving error)
E5 – Remote control transmission error (transmitting error)
EA-  indicates a mis-wiring or overloading problem.
EC- Start-up time over

EF- M-NET transmission error

P1    Room temperature thermistor (TH1) is abnormal.
P2    Error detail Abnormality of pipe temperature thermistor/liquid (TH2).
P4    Error detail Abnomarlity of drain sensor (DS)
P5    Error detail Malfunction of the drain-up machine.
P6    Error detail Freezing/overheating protection detect.
P8    Error detail Abnormality of pipe temperature.
P9    Error detail Abnormality of pipe temperature thermistor/condenser/evaporator (TH5)
F1    Reverse phase detection.
F2    L3 open phase detection.
F3    63L connector open
F4    49C connector open
F9    Connector 2 or more open.
FA    L2-phased open phase or 51CM connector open
F7    Reverse phase detection circuit (p.c.board) fault.
U0    Abnormal low voltage.
U1    Abnormal high pressure (high-pressure switch 63H worked)
U2    Abnormal high discharging temperature.
U2    Inner thermostat (49C) operation.
U3    Discharge thermistor short/open.
U4    Outdoor thermistor short/open.
U6    Compressor overcurrent (overload) cut off.
UA    Compressor over current (terminal relay operation).
UF    Compressor over current (start-up locked) cut off
UE    High-pressure error (ball valve closed)
UL    Abnormal low pressure
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