Mitsubishi Mini-Split Error Codes: What Each Code Means and What to Do

When a Mitsubishi mini-split detects a fault, it either displays an alphanumeric code on the indoor unit’s display panel (newer units), shows a blinking pattern on the operation indicator light (older units), or both. The remote control may also show the code in the display.

Most codes divide into three categories:

• Sensor codes (P-series): temperature sensor failures — usually the sensor or wiring, sometimes a refrigerant condition
• Communication codes (E-series / U-series): lost signal between indoor and outdoor unit — wiring, connection, or matched-unit issue
• Protection codes: the system detected a condition outside normal limits and shut down as a safety measure

The code chart in your installation manual is the T0 authority. Codes vary between product generations. This guide covers the most common codes on US-market M-Series residential units.

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How to read Mitsubishi mini-split error codes

Units with a display panel (most units 2015+): The code appears directly on the indoor unit’s display — typically in the form “E6”, “P6”, “U1”, or similar. Some remotes also show the code when you press STATUS or CHECK.

Units without a display (older units, some ceiling cassettes): The operation indicator LED blinks in patterns. The TIMER and OPERATION lights may both blink together, or alternate, to signal different faults. The specific blink sequence maps to codes in your installation manual — the pattern varies enough between models that you need the manual to decode it reliably.

To clear a non-critical code and attempt restart: Turn the unit off from the remote. Wait 3–5 minutes. Turn it back on. If the code returns immediately, the condition is still present. If it clears and the unit runs, monitor for recurrence.

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Mitsubishi mini-split error codes: the most common

E6 — Indoor/outdoor communication error

The indoor and outdoor units have lost communication. The communication line (typically a 2-wire or 3-wire control cable) carries the signal that coordinates operation.

What to check first:

1. Inspect the communication wire connections at both the indoor and outdoor unit terminals. Mini-splits have a dedicated communication terminal block (often labeled S1, S2, S3 or T1/T2/T3). Loose or corroded terminals are a common cause after years of outdoor exposure.
2. Check for physical damage to the communication cable where it runs outside — UV degradation, pest damage, pinching at wall penetrations.
3. Verify indoor/outdoor unit compatibility. An E6 that appears after equipment was serviced may indicate a mismatched replacement outdoor unit was installed.
4. Check for AC power to both units. If the outdoor unit lost power (tripped breaker, loose disconnect), E6 will appear even if the wiring is intact.

E6 that persists after inspecting connections typically requires a technician to test the communication circuit with a meter and potentially replace the control board.

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E7 — Indoor unit fan motor fault

The indoor unit’s fan motor is not running at the expected speed, or the control board cannot detect the motor’s feedback signal.

What to check:

• With the unit off, gently spin the indoor blower (the cylindrical drum inside the indoor head) by hand. It should spin freely. If it’s stiff or grinds, the motor bearing is failing.
• Check that nothing is blocking the blower — debris, a bent fin, or a displaced panel.

E7 usually requires motor replacement by a technician. Mini-split blower motors are DC variable-speed motors that are not field-serviceable on most units.

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P1 — Room temperature sensor fault

The thermistor (temperature sensor) that measures room air temperature has failed or is reading outside its expected range. Room temperature sensors are inexpensive parts and can fail from corrosion or physical damage.

What to check:

• Inspect the sensor wire where it connects to the control board inside the indoor unit. Loose, corroded, or broken connector = likely cause.
• P1 that appears after a cleaning service may indicate a sensor was dislodged or disconnected.

A technician can test the sensor resistance vs. the expected curve and replace it if failed (~$20–40 part, plus labor).

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P2 — Evaporator (indoor coil) temperature sensor fault

The thermistor measuring the indoor coil temperature has failed. Similar to P1, but measuring the coil rather than the room.

What to check: same as P1 — connector integrity at the control board. The evaporator sensor clips onto the coil fins; check that it’s properly seated.

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P4 — Drain sensor fault (units with drain sensor)

The condensate level sensor has detected a potential drain overflow, or the sensor itself has failed. Not all models have this sensor.

What to check:

1. Check the condensate drain first. A clogged drain pan or drain line is the most common trigger. The pan fills, the sensor detects the water level, and the unit shuts down as a flood-prevention measure.
2. Clear the drain: locate the drain hose exiting the indoor unit (usually a small diameter PVC or vinyl hose), remove any visible blockage, and flush gently with water. On a clean installation, pour a cup of water into the drain pan to confirm it drains.

P4 caused by a blocked drain is DIY-appropriate. A false P4 on a clear drain indicates sensor failure — call a tech.

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P6 — Freezing protection / over-cooling

The unit detected abnormally low temperature at the indoor coil, triggered the freeze protection mode, and stopped cooling. This is one of the most common codes homeowners encounter.

What causes P6:

1. Airflow restriction — dirty air filter or blocked return path. This is the most common cause and the only DIY fix.
2. Low refrigerant — if refrigerant is undercharged, the evaporator pressure drops and the coil freezes. This requires a technician with gauges.
3. Very low outdoor temperature during cooling — most mini-splits don’t cool reliably below ~15°F outdoor. In shoulder seasons or cold nights, P6 may appear if the unit is running in cooling mode at low ambient.
4. Defrost activation — heat pump units entering a defrost cycle may briefly show P6 behavior; this is normal and clears automatically.

What to check:

1. Clean or replace the air filter. The filter is in the indoor unit behind the front panel — typically a washable mesh filter. Rinse, let dry, reinstall.
2. Allow the coil to thaw. Turn the unit to FAN ONLY mode (no cooling) or turn it off entirely and let it run fan-only for 30–60 minutes to melt any ice. Do not run cooling until all ice is gone.
3. If the filter is clean and P6 returns within a cooling cycle, refrigerant undercharge is likely. Call a tech.

Note: adding refrigerant to a mini-split requires EPA 608 certification, proper recovery equipment, and accurate weighing in. Never let an untrained person “top off” a mini-split — overcharge is as damaging as undercharge.

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P8 — Outdoor temperature sensor fault (some models)

The sensor measuring outdoor air temperature has failed. Similar to P1/P2, this is a sensor or connector issue. A tech can test resistance vs. expected temperature curve and replace the sensor.

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U1 — Overcurrent protection

The compressor or outdoor unit motor drew excessive current. Causes include a failing compressor, low voltage at the outdoor unit, or refrigerant issues causing abnormal operating pressures.

Call a tech. U1 requires checking compressor amperage, supply voltage, and refrigerant pressures with professional equipment.

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U2 — Abnormal power supply voltage

The unit detected voltage outside its acceptable range (too high or too low). Check:

• Is the outdoor unit’s dedicated circuit breaker fully seated?
• Is the disconnect switch at the outdoor unit closed?
• Other appliances on the same circuit (unusual for a dedicated mini-split circuit, but possible in older wiring)

If voltage is confirmed normal and U2 persists, the unit’s power board may be failing — call a tech.

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U3 / U4 — Communication error variants

Similar to E6 — communication failure between indoor and outdoor unit, or between the control board and a sub-component. Check connections first; if persistent, requires control board testing by a tech.

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The “FILTER” light is not an error code

A blinking or illuminated FILTER light is a maintenance reminder, not a fault. The unit tracks operating hours and illuminates this light after a set interval (typically 250 hours of runtime) to prompt filter cleaning. Clean or rinse the filter, then:

• Press the FILTER RESET button on the remote control (usually a small button labeled FILTER)
• Or hold the FILTER RESET button on the indoor unit itself for 2–3 seconds

If the filter light is illuminated AND the unit isn’t cooling well, clean the filter first — low airflow from a dirty filter causes both the light and reduced performance.

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When to call a licensed HVAC tech

Any code related to refrigerant (P6 that returns after filter cleaning, U1), compressor faults, or communication errors that persist after checking connections should be handled by a technician. Specific conditions that require a pro:

• P6 returns with a clean filter — likely low refrigerant charge; requires EPA 608 certified technician with refrigerant scale and gauges
• E6 / U3 / U4 after checking connections — control board or communication cable failure
• U1 — overcurrent; compressor testing required
• U2 with confirmed normal voltage — power board failure
• Any code appearing with a refrigerant odor or hissing sound — refrigerant leak; turn the unit off and call a tech

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Cost guide

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FAQ

My Mitsubishi mini-split is blinking 6 times. What does that mean? On units without a display panel, the blink count maps to a code that varies by model generation. A 6-blink pattern may correspond to E6 on some models, but you need to check the specific pattern against your installation manual’s blink-code chart. Open the manual to the “Troubleshooting” section — the blink pattern table lists each sequence and its meaning.

Can I reset a Mitsubishi mini-split to clear an error? Yes — turn the unit off from the remote, wait 5 minutes, turn it back on. This clears the active fault and restarts the system. If the fault condition is still present (dirty filter, blocked drain, failed sensor), the code will return.

My unit shows an error code but still seems to be running. Should I stop it? Some codes are warnings (like FILTER), others are active faults. If the code is a P-series protection code and the unit is running, it may be in a degraded mode. Don’t rely on a unit showing an active fault code without investigating — running a unit with low refrigerant can damage the compressor.

The error code isn’t in this guide. Where can I find it? Mitsubishi publishes installation and service manuals for each product line. Find your model number on the indoor unit’s nameplate (behind the front panel) and search for “[model number] service manual PDF.” Mitsubishi Electric US also maintains a resource library at mehvac.com. The error code table in the installation manual covers every code for that unit.

Does the Mitsubishi Kumo Cloud app show error codes? If the unit is connected to a Kumo Cloud controller (Mitsubishi’s smart home interface), diagnostics and fault codes are visible in the Kumo Cloud app or through an MHK2 remote. This is the easiest way to access error history without opening the indoor unit.