When your Mitsubishi air conditioner shows an error code, it’s the system’s way of telling you something is wrong—before things get worse. Knowing what codes mean, what causes them, and how to fix them (or when to call in help) can save you time, stress—and money.
Here’s a detailed guide covering Mitsubishi AC error codes: what each code means, common causes, troubleshooting steps, and best practices.
How Mitsubishi AC Error Codes Work
- Codes are usually alphanumeric (letters + number) or sometimes 4-digit numeric, depending on model.
- They can be shown on the indoor unit’s display, the remote controller, or via LED blink codes on control boards.
- Some error codes are generic, others are model-specific (e.g. Mr. Slim, Multi-split, ductless, etc.). Always check your unit’s manual.
What Happens When an Error Code Appears
- The unit may shut down or go into a “safe mode” to prevent damage.
- Performance will degrade (e.g. less cooling/heating, strange noises, no airflow, etc.).
- Ignoring error codes can result in more serious issues—compressor damage, electrical faults, refrigerant leaks, etc.
Common Mitsubishi AC Error Codes & What They Mean
Here’s a breakdown of common error codes, grouped by code-type, with likely causes and what to check / do. These lists are derived from Mitsubishi Electric sources and HVAC service documentation.
| Error Code | What It Means / Description | Likely Causes | What to Do / Troubleshoot |
|---|---|---|---|
| P-Series / Sensor & Safety Codes | |||
| P1 | Intake (room) air thermistor / sensor error | Faulty or disconnected room temp sensor; wiring issue; damage; moisture ingress | Check probe / sensor connection; measure resistance vs spec; replace sensor if needed. Ensure sensor is clean and dry. |
| P2 – P9 | Pipe (liquid, 2-phase, or gas pipe) thermistor / sensor error | Sensor open or short; wiring damage; sensor mis-positioned; pipe insulation issues; exposure to heat or cold outside range. | Test sensor resistance; inspect wiring; ensure correct installation; replace sensor if faulty. |
| P4 | Drain sensor error | Water in drain pan or float switch; blocked drain; sensor fault. | Clean / clear drain line; check float switch; verify sensor works; ensure proper slope of drain line. |
| P5 | Drain pump fault | Pump jammed; pump not receiving power; obstruction; clogged filter. | Check pump operation; ensure power is reaching it; remove blockages; replace if needed. |
| P6 | Freezing or overheating safeguard triggered | Poor airflow; dirty filters; low refrigerant; outdoor or indoor unit too cold/hot; blocked coil; fan issue. | Clean filters; ensure airflow; inspect coil; check refrigerant levels; ensure fan motors are functioning. |
| P8 | Pipe temperature error | Thermistor error; pipe temp out of range; sensor wiring. | Similar to P2-P9: inspect, test, replace; check for extreme ambient temps or load. |
| U / Over-Current / Pressure / Thermistor / Inverter Codes | |||
| U1, Ud | High pressure or overheating safeguard operation | Overcharge; blocked outdoor coil; high ambient temp; condenser fan not working; pressure switch triggers. | Clean condenser; check fan; check refrigerant charge; inspect pressure switches. |
| U2 | Abnormal high discharge temperature / possible low refrigerant or insufficient cooling load | Refrigerant low; condenser dirty; fan issue; compressor overwork. | Check refrigerant; clean coils; ensure airflow; test compressor performance. |
| U3 / U4 | Discharge thermistor or outdoor thermistor short / open circuit | Sensor damaged, disconnected, wiring short/open; environmental damage. | Test resistance; inspect wiring and connectors; replace sensor if needed. |
| U5 | Abnormal temp of heat sink / inverter heatsink overheating | Heat sink dirty or blocked; fan not blowing; unit overloaded; ambient too hot. | Clean/clear heatsink; ensure fan operation; allow unit to cool; possibly reduce load; ensure unit has ventilation. |
| U6 | Compressor overcurrent interruption / power module abnormality | Electrical overload; stuck compressor; short in motor windings; power supply issues. | Check current draw; inspect wiring; ensure supply voltage stable; replace power module if needed. |
| U7 | Superheat abnormality due to low discharge temperature | Possibly refrigerant issues, sensor calibration, evaporator coil frost, etc. | Check evaporator and refrigerant flow; sensors; defrost cycle. |
| U8 | Outdoor unit fan safeguard stop (fan failure or blockage) | Fan motor failure; obstruction (debris, ice); wiring issue. | Inspect fan; remove debris; test fan motor; repair/replace if broken. |
| U9 / UH | Over-voltage, under-voltage, current sensor error, or synchronous signal issues (electrical / communication faults) | Power instability; wiring issues; sensor faults; board errors. | Check mains voltage; inspect wiring; test sensors; consider replacing control PCB. |
| E / Remote / Communication / Address / Controller Errors | |||
| E0 – E3 | Remote controller signal / transmission error | Remote battery dead; remote signal blocked; remote control board malfunction; wiring / IR receiver issue. | Replace batteries; test remote; check receiver; ensure remote is within range; replace remote board if needed. |
| E4 | Remote controller signal receiving error | Remote signal not reaching indoor unit; IR/receiver issue; wiring. | See E0–E3 steps; focus on indoor IR sensor / remote to indoor link. |
| E6-E7 | Indoor / outdoor unit communication error | Broken communication wires; connectors loose; PCB failure; interference. | Inspect comms wiring; check connectors; reset units; possibly replace PCB. |
| E8-E9 / EC etc | Communication errors (transmission, receiving) affecting remote/outdoor/indoor units | Same as above; sometimes caused by address conflict or mismatch in settings. | Verify unit addressing; check wiring; reset; ensure compatible firmware or module. |
| EA, EB, EC, etc. | Mis-wiring; exceeded number of indoor units; start-up time over; address / attribute setting errors | Incorrect installation; configuration errors; remote / controller setting mismatches. | Check installation wiring; ensure system configured correctly (addresses, settings); update/wire as per manual. |
| Miscellaneous / Advanced / Model-Specific Codes | |||
| 1301 | Low pressure fault | Leak; undercharged refrigerant; blocked filter or capillary; evaporator coil issues. | Pressure check; leak test; top-up refrigerant; ensure filters clean. |
| 1302 | High pressure fault | Condenser blocked; high ambient heat; fan problem; overcharge. | Clean condenser; check fan; reduce load; verify charge. |
| 1500 | Refrigerant overcharge (or system detecting too much refrigerant) | Installation error; cylinder over-filled; expansion device issue. | Recover and correct refrigerant load; check sensors and pressure switches. |
| 2500, 2502, 2503 | Drain sensor submergence / drain pump / sensor issues | Water log; pump failure; sensor mis-reading. | Clear water; test pump; replace faulty sensors. |
| 2600 | Water leak / condensate leak detected | Leak in drain pan; pipe disconnected; hose blocked/deteriorated. | Inspect drain system; seal leaks; reconnect hoses; ensure correct slope. |
| 4102, 4106, 4115, etc. | Compressor overcurrent / RPM errors / transmission power supply fault / motor errors | Motor overload; fan locked; poor power supply; wiring issues; sensor signals wrong. | Measure current; inspect motor; ensure power supply stable; replace motor or control module. |
| 5101, 5102, etc. | Thermistor faults / sensor open or short circuits | Sensor failure, wire damage, moisture, short/ground fault. | Test resistances; replace sensors; ensure wiring protected. |
Troubleshooting: What to Check First
Before calling a technician, here are steps you can try:
- Turn off power – switch off breaker or isolator for AC unit. Wait several minutes (5-10) then restart. Sometimes resets minor faults.
- Clean filters, coils & vents – many error codes stem from blocked airflow / dirty equipment.
- Check sensors & wiring – look for loose plugs, damaged wires, moisture, corrosion.
- Inspect outdoor unit – is it obstructed? Is the fan spinning freely? Is the condenser coil dirty?
- Check refrigerant pressure – low or high refrigerant often triggers pressure / discharge temp errors. Professionals needed for safe handling.
- Verify remote / communication settings – batteries, IR signal, settings, remote unit address settings.
- Check power supply – voltage stability, phase correctness (if applicable), proper wiring.
When You Need a Professional
You should contact a qualified HVAC / Mitsubishi Electric service tech when:
- Refrigerant leaks or pressure issues.
- Compressor doesn’t run or is locked.
- PCB or inverter failures.
- Intermittent communication faults that don’t clear.
- Electrical hazards.
- Warranty-related repairs (to avoid voiding warranty).
Best Practices to Prevent Error Codes
- Regular maintenance: cleaning, inspecting, servicing.
- Annual check of refrigerant charge and electrical connections.
- Using Mitsubishi approved parts / sensors.
- Ensuring the outdoor unit has space / airflow, is protected from debris and weather.
- Protecting from power spikes (voltage surge protection).
Conclusion
Mitsubishi AC units are robust and well-engineered, but no system is perfect. Error codes exist as an early warning mechanism. Understanding what the code means, what typically causes it, and how to address it can help maintain performance, extend lifespan, and avoid costly repairs. Always refer to your specific model’s manual for exact specifications, and when in doubt, bring in a certified technician.
