Quick answer
Mitsubishi mini split error codes use a letter plus a number: P and E codes usually point to the indoor unit or communication, and U codes point to the outdoor unit. The most common ones homeowners see are E6 (indoor and outdoor units aren’t communicating), P8 (pipe temperature problem, often airflow or refrigerant), U4 (outdoor sensor fault) and P5 (drain pump problem). A power reset at the breaker clears some codes, but if the same code returns, the unit needs a technician.
Codes vary by model and series. The tables below follow the self-diagnosis lists in Mitsubishi’s Mr. Slim and M-Series installation and service manuals. Always confirm against the manual for your exact model number (printed on the label on the side of the indoor and outdoor units). Commercial City Multi systems use four-digit codes (like 6831 or 2502) and aren’t covered here.
How to read the error code on your Mitsubishi
With a wired remote or wall controller: the code shows on the screen. On many controllers you can also press the CHECK button twice to enter self-diagnosis; after a few seconds the stored code appears. Press ON/OFF to exit.
With a wireless (IR) remote: most units support a self-check mode, started by pressing the remote’s CHECK button (on some remotes it’s recessed and needs a pen tip). Point the remote at the unit; it beeps to confirm, then the operation light blinks and the unit beeps a number of times. Count the blinks in one full cycle (the pattern repeats after a pause) and match the number to the tables below.
Wall-mounted M-Series units (MSZ): these often signal faults by blinking the operation indicator lamp without a remote. Watch at least two full cycles and count the blinks. Blink meanings for these units vary by model, so match the count against the troubleshooting section of your unit’s service manual.
Tip: write down the code, the date, and what the unit was doing (heating, cooling, defrost). A technician can diagnose much faster with that information.
Indoor unit codes (P and E)
These codes are detected by the indoor unit. The “Blinks” column is the number of beeps or operation-light blinks in self-check mode on units that use this pattern (often listed as output pattern A in Mitsubishi manuals).
| Code | Blinks | Meaning | First thing to try | DIY or pro? |
|---|---|---|---|---|
| P1 | 1 | Intake (room air) temperature sensor error | Power reset at the breaker | Pro if it returns (sensor or board) |
| P2 / P9 | 2 | Pipe (coil) temperature sensor error | Power reset | Pro (sensor or wiring) |
| E6 / E7 | 3 | Indoor–outdoor communication error | Power reset; check that the outdoor unit has power | Pro if it returns (wiring, fuse or board) |
| P4 | 4 | Drain sensor / float switch error | Check for water in the drain pan; clear the drain line | Often DIY-clearable; pro if it returns |
| P5 | 5 | Drain pump error | Check for a clogged drain line or full condensate pump | Often DIY-clearable; pro for pump replacement |
| P6 | 6 | Freezing or overheating safeguard tripped | Clean the filter; clear indoor and outdoor airflow | DIY first; pro if it returns |
| P8 | 8 | Pipe temperature error (coil temperature not behaving as expected) | Clean filters and coils; clear the outdoor unit | Pro if it returns (refrigerant or sensors) |
| E4 / E5 | 9 | Remote controller signal receiving error (wired remote) | Check remote wiring and connections | Pro |
| E0 / E3 | — | Remote controller transmission error | Replace remote batteries; reset power | DIY first |
| E1 / E2 | — | Remote controller board error | Reset power | Pro if it returns |
| PA | — | Forced compressor stop (often tied to a water leak or drain fault) | Check the drain pan and line | Pro |
| Pb | — | Indoor fan motor error | Turn off and check for obstructions in the blower | Pro |
| Fb | — | Indoor unit control board error (e.g. memory error) | Power reset | Pro (board) |
Codes are taken from Mitsubishi’s Mr. Slim installation and service manuals; wall-mounted MSZ units may label faults differently. A dash means the blink count isn’t consistent across models — check your manual.
Outdoor unit codes (U and E9)
These codes are detected by the outdoor unit. In self-check mode on many models, the blink pattern for outdoor faults is different from indoor ones (often listed as output pattern B, with a longer initial light). Count the blinks and match below.
| Code | Blinks | Meaning | First thing to try | DIY or pro? |
|---|---|---|---|---|
| E9 | 1 | Indoor–outdoor communication error (outdoor side) | Power reset; check the outdoor disconnect | Pro if it returns |
| UP | 2 | Compressor overcurrent shutdown | Power reset once; clear the outdoor unit | Pro |
| U3 / U4 | 3 | Outdoor temperature sensor (thermistor) open or shorted | Power reset | Pro (sensor or board) |
| UF | 4 | Compressor overcurrent — compressor locked | Do not keep resetting | Pro |
| U2 | 5 | Abnormally high compressor discharge temperature, often low refrigerant | Clear outdoor airflow | Pro (refrigerant check) |
| U1 / Ud | 6 | Abnormally high pressure or overheat protection | Clean the outdoor coil; clear blockages; check the indoor filter in heating | Pro if it returns |
| U5 | 7 | Inverter heat sink temperature too high | Clear the outdoor unit; check that the outdoor fan spins | Pro |
| U8 | 8 | Outdoor fan protection stop | Check for ice, snow or debris on the fan | Pro if the fan won’t spin |
| U6 | 9 | Compressor overcurrent or power module fault | Power reset once | Pro |
| U7 | 10 | Abnormal superheat from low discharge temperature | — | Pro (refrigerant circuit) |
| U9 / UH | 11 | Supply voltage abnormality or current sensor error | Check for brownouts; reset the breaker | Pro if it returns; electrician if voltage is unstable |
Outdoor-unit codes mostly involve the compressor, refrigerant circuit, sensors or power electronics. Apart from clearing debris, ice and power problems, they’re jobs for a licensed technician.
Fixes for the most common codes
E6 — indoor and outdoor units aren’t communicating
E6 is the code homeowners search for most. The indoor unit sends signals to the outdoor unit over a communication wire; E6 means that conversation broke down.
Common causes: a power interruption or surge, a tripped outdoor breaker or disconnect, a loose or corroded wire at the terminal block, a blown fuse on the outdoor board, a failed control board, or wiring damaged by pests or weather. On new installs, incorrect wiring between units is a frequent cause.
What to do:
- Turn the system off at the remote.
- Switch off the breaker(s) for the mini split, wait 3–5 minutes, and switch them back on.
- Confirm the outdoor disconnect is on and the outdoor unit gets power.
- If E6 returns, call a technician to check the wiring, terminal connections, fuse and boards. Don’t open the terminal covers yourself — the communication wire on Mitsubishi systems carries line voltage.
P8 — pipe temperature error
P8 means the coil temperature isn’t changing the way the unit expects once the compressor runs. It’s often an airflow problem, but it can also mean low refrigerant or a sensor issue.
What to do: clean the indoor filters, make sure nothing is blocking the indoor unit’s airflow, and clear snow, leaves and debris from around the outdoor unit. Reset power. If P8 returns, have a technician check the refrigerant charge, sensors and the outdoor coil.
U4 — outdoor sensor fault
U4 (and the related U3) usually means one of the outdoor unit’s temperature sensors (thermistors) is reading open or shorted — from a failed sensor, a loose connector, or a control board problem.
What to do: reset power once. If U4 comes back, a technician needs to test the outdoor thermistors and connectors. A sensor is a relatively inexpensive part; a board costs more.
P4 and P5 — drain sensor or drain pump errors
Mostly on ceiling cassettes and ducted units with condensate pumps. The unit stops to avoid a water leak when the drain sensor detects a high water level or the pump fails.
What to do: turn the unit off and look for water in the drain pan or dripping from the unit. Clear the condensate line (a wet/dry vacuum on the outside end of the line often pulls out the clog), and clean any algae from the pan. If the error persists, the pump or float switch may need replacing.
P6 — freezing or overheating protection
The indoor coil got too cold (cooling) or too hot (heating), so the unit protected itself. Restricted airflow is the usual cause.
What to do: clean the filters, open any closed vanes, and make sure furniture or curtains aren’t blocking the unit. In cooling, let any ice on the coil melt fully before restarting. If P6 recurs with clean filters, the cause may be low refrigerant or a fan problem.
U2 — high discharge temperature
The compressor is running too hot, very often because the system is low on refrigerant from a leak.
What to do: clear the area around the outdoor unit and reset once. Don’t keep resetting a recurring U2 — running a compressor that overheats repeatedly can damage it. Call a technician for a leak check.
How to reset a Mitsubishi mini split
- Turn the unit off with the remote.
- Switch off the breaker(s) for the indoor and outdoor units (and the outdoor disconnect if you prefer).
- Wait 3–5 minutes so the control boards fully discharge.
- Turn the power back on, wait a minute, then turn the unit on with the remote.
- Give it 10–15 minutes. The compressor has a built-in startup delay, so the outdoor unit may not start right away.
A reset clears glitches from power blips or surges. If the same code comes back, don’t keep resetting — especially for compressor-related codes (UP, UF, U2, U6), where repeated restarts can cause more damage.
When to call a technician
- The same code returns after a reset
- Any compressor, overcurrent or power-module code (UP, UF, U6, U5)
- Codes pointing to refrigerant problems (U2, U7, or a recurring P8)
- Water leaking from the indoor unit
- Burning smells, buzzing, or a breaker that trips again
Look for a Mitsubishi Diamond Contractor or another installer experienced with Mitsubishi systems; they can read stored fault history and have access to model-specific service manuals. If your system is under warranty, call the original installer or Mitsubishi first — unauthorized repairs can affect coverage.
Typical repair costs
Approximate 2026 US prices, parts and labor:
| Repair | Typical cost |
|---|---|
| Diagnostic visit | $100–$250 |
| Clear condensate line / drain pan cleaning | $100–$250 |
| Condensate pump replacement | $200–$450 |
| Thermistor (temperature sensor) replacement | $150–$400 |
| Communication wire repair or replacement | $150–$600 |
| Indoor or outdoor control board | $400–$1,200 |
| Indoor fan motor | $350–$900 |
| Outdoor fan motor | $400–$900 |
| Refrigerant leak repair + recharge | $400–$1,500+ |
| Compressor replacement | $1,500–$3,500 (often not worth it on older units) |
Many Mitsubishi parts are covered for 10 years or more when the system was registered or installed by a Diamond Contractor, so check your warranty before paying for parts.
Frequently asked questions
What does E6 mean on a Mitsubishi mini split?
E6 is an indoor–outdoor communication error. Reset power at the breaker; if it returns, a technician needs to check the communication wiring, fuses and control boards.
What does P8 mean on a Mitsubishi mini split?
P8 is a pipe temperature error: the coil temperature isn’t changing as expected. Start with clean filters and a clear outdoor unit; if it returns, have the refrigerant charge and sensors checked.
What does U4 mean on a Mitsubishi mini split?
U4 usually indicates an outdoor temperature sensor (thermistor) that’s open or shorted. It needs a technician to test the sensors and connectors.
Why is the green light blinking on my Mitsubishi mini split?
A slow, steady blink can simply mean the unit is in standby or starting up. A repeating pattern of blinks with a pause usually signals a fault code. Count the blinks over two cycles and check the tables above or your manual.
How do I clear an error code on my Mitsubishi mini split?
Turn the unit off, switch off the breaker for 3–5 minutes, then restore power. If the underlying problem is still there, the code will come back.
Are Mitsubishi error codes the same on all models?
No. Mr. Slim and many M-Series units share the P, E and U codes above, but wall-mounted MSZ units often use blink counts with model-specific meanings, and City Multi commercial systems use four-digit codes. Always check your model’s manual.
Related guides
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- Mitsubishi Hyper-Heat Review: Real-World Cold-Weather Performance
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Codes are compiled from Mitsubishi Electric installation and service manuals and may differ on your model. This guide is general information; leave electrical, refrigerant and internal repairs to a licensed HVAC technician. ElectrifyHomeGuide is not affiliated with Mitsubishi Electric. Repair prices are approximate 2026 national ranges.