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Mitsubishi Electric air conditioner error codes

22 codes that Mitsubishi Electric publishes for its air conditioners, each with what it means, the likely cause, what you can safely check and when to call an installer. Tap your code:

Air conditioner: do only the checks the maker gives the owner for that code — clean the air filter, clear the air path, switch the power off and on at the plug or circuit breaker. Keep the covers on: refrigerant, wiring and circuit boards are not owner work. Anything else is for the installer or the maker’s service engineer: in the UK and EU only an F-gas certified technician may open the refrigerant circuit. Codes that need one are marked Installer.

Read this first

Mitsubishi Electric air conditioners show a fault in two ways. Mr Slim units with a wired remote controller show a check code such as P8 or E6 on its screen; with a wireless remote the same code is given by the number of times the indoor unit beeps and its OPERATION INDICATOR lamp blinks (5 blinks is P5 for an indoor fault, or U2 for an outdoor one). The codes below come from Mitsubishi Electric’s installation manual for its PKA-M wall-mounted Mr Slim units; the operation manual for the same units tells the owner not to repair anything and to call the dealer. Mitsubishi Electric’s M Series wall units (MSZ) use blinking lamps rather than letter codes, and their pattern tables are in service manuals. Models differ: your model’s manual is the authority.

P8 Pipe temperature error

What it means
The indoor unit’s pipe temperature is not what the unit expects for the mode it is running in (8 blinks on a wireless remote).
Likely cause
The manual gives no further cause for owners; it is for the installer to trace.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Turn off the power switch and consult your dealer or installer, giving them the model name and the code.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

P1 Intake air sensor error

What it means
The sensor that measures the air drawn into the indoor unit has failed (1 blink on a wireless remote).
Likely cause
A faulty intake sensor or its connection.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

P2 P9 Pipe sensor error

What it means
A refrigerant pipe temperature sensor in the indoor unit has failed: P2 the liquid-pipe sensor (TH2), P9 the dual-wall pipe sensor (TH5). Both are 2 blinks on a wireless remote.
Likely cause
A faulty pipe sensor or its connection.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

P4 Drain sensor error

What it means
The drain sensor has failed, or the drain float switch connector (CN4F) is disconnected (4 blinks).
Likely cause
A faulty drain sensor or a loose float-switch connector.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer: the connector is on the indoor controller board.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

P5 Drain pump error or drain overflow

What it means
The drain overflow protection has operated, or the drain pump has failed (5 blinks).
Likely cause
Condensate is not draining away from the indoor unit.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Turn off the power switch and consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

P6 Freezing or overheating protection

What it means
The indoor coil became too cold while cooling or too hot while heating, and the protection operated (6 blinks).
Likely cause
The manual names only the protection that operated.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

PA Refrigerant leak error or forced compressor error

What it means
The installation manual lists PA as a leakage error in the refrigerant system on the wired remote, and as a forced compressor error in the wireless (blink) table.
Likely cause
A refrigerant leak, or a compressor forced to stop.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer. A refrigerant leak may only be found and repaired by an F-gas certified technician.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

Pb Indoor fan motor error

What it means
The indoor unit’s fan motor has a fault (11 blinks).
Likely cause
A fan motor or fan circuit fault.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

PL Refrigerant circuit abnormal

What it means
The unit has detected an abnormality in the refrigerant circuit (14 blinks).
Likely cause
A fault in the refrigerant circuit.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer: the refrigerant circuit is F-gas certified work.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

FB Indoor controller board error

What it means
The indoor unit’s controller board has a fault, such as a memory error (12 blinks).
Likely cause
An indoor control-board fault.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

E6 E7 Indoor–outdoor communication error

What it means
The indoor and outdoor units are not communicating (3 blinks). The wired-remote table covers the whole range E6 to EF for this fault, except EE (7 blinks), a communication error of its own.
Likely cause
A wiring or communication fault between the units.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Turn off the power switch and consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

E0 E3 Remote controller communication error

What it means
The remote controller and the indoor unit are not communicating (the wired-remote table gives E0 to E5 for this).
Likely cause
A remote controller transmission fault.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

U2 Outdoor unit: high discharge temperature

What it means
An outdoor-unit fault: abnormally high discharge temperature, the 49C protection has worked, or there is too little refrigerant (5 blinks in the outdoor pattern).
Likely cause
Overheating in the compressor circuit; one listed cause is too little refrigerant.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer: a refrigerant shortage is F-gas certified work.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

U1 Ud Outdoor unit: high pressure

What it means
An outdoor-unit fault: abnormally high pressure (the 63H switch worked) or overheating protection (6 blinks in the outdoor pattern).
Likely cause
Too high a pressure in the refrigerant circuit.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

U3 U4 Outdoor unit: thermistor open or shorted

What it means
An outdoor-unit temperature sensor (thermistor) is open- or short-circuited (3 blinks in the outdoor pattern).
Likely cause
A failed outdoor thermistor or its wiring.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

UP UF Outdoor unit: compressor overcurrent

What it means
The compressor’s overcurrent protection interrupted it — UF when the compressor is locked.
Likely cause
A compressor overcurrent or a locked compressor.
What you can safely check

Nothing for the owner to check: this one is for an installer.

When to call an installer
Installer Consult your dealer or installer.

Source: Mitsubishi Electric, Mr Slim PKA-M35-50LA2 Installation Manual (VG79Y436H01): 7 Test run — self-check and check codes Checked 2026-09-29.

A code that is not listed here

For any check code not listed here, Mitsubishi Electric’s operation manual gives one instruction: the protection devices have operated to protect the air conditioner, so do not try to repair it yourself — turn off the power switch and consult your dealer, giving them the model name and what the remote controller shows. Codes starting U or F (except FB) are outdoor-unit faults; their details are in the outdoor unit’s documents.

We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.

Related pages

Source

Every code on this page comes from these pages, published by Mitsubishi Electric and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.