When an issue occurs with a Mitsubishi air conditioner, an error code or flashing LED pattern will display on the indoor unit panel or wired remote controller. Understanding these diagnostic prefixes helps identify the fault category quickly:
- P Series: Indoor unit sensor, drainage, and freeze protection faults
- E Series: Remote controller and indoor-outdoor communication errors
- U Series: Outdoor compressor, thermistor, and high-pressure protection faults
- F Series: Control system, memory, and power phase errors
1. How to Read & Reset Your Mitsubishi Display
- Switch Off Main Power: Shut down the aircon using the wall isolator or main distribution board switch (avoid relying only on the wireless remote).
- Wait for Full Discharge: Keep the system powered down for 5 minutes to clear system memory and safely discharge electrical components.
- Power Back On & Observe: Turn the power back on and run the unit. If the error code or flashing lights reappear, an active hardware or environmental fault requires professional intervention.
2. Complete Mitsubishi Error Code Reference Table
| Code | Meaning / Likely Cause | Severity | Recommended Action | Typical SG Cost |
| P1 | Intake / Room Temperature Sensor Error | Medium | Inspect and replace defective room thermistor or wiring. | From $130 |
| P2 / P9 | Pipe (TH2 / TH5) Temperature Sensor Error | Medium | Test evaporator coil sensor resistance; replace if faulty. | From $130 |
| P4 / P5 | Drain Pump Error / Float Switch Open | Medium | Vacuum drain lines and clear clogged condensate pump or pan. | From $90 |
| P6 | Freeze Protection / Overheat Safeguard | Medium | Clean dirty air filters immediately to restore proper airflow. | $40 – $90 (Servicing) |
| E1 / E2 | Remote Controller Control Board Error | Medium | Check wired controller connections or replace faulty controller board. | $150 – $300 |
| E6 / E7 | Indoor/Outdoor Communication Error | High | Check outdoor isolator, tighten loose terminal signal wires. | Free check – $350 |
| U1 / Ud | Abnormal High Pressure / Overheating | High | Clean condenser coils; check for airflow blockage or system overcharge. | $90 – $180+ |
| U2 | High Discharge Temp / Insufficient Refrigerant | High | Perform pressure test to locate leaks before topping up gas. | From $180 |
| U3 / U4 | Outdoor Thermistor Open or Short | Medium | Inspect outdoor sensor wiring and replace damaged condenser thermistor. | From $130 |
| U8 | Outdoor Unit Fan Protection Stop | Medium | Inspect outdoor fan motor for obstructions or jammed blades. | $200 – $350 |
| UF / U6 | Compressor Overcurrent / Locked Rotor | High | Inspect power module, inverter board, or compressor health. | $300 – $600+ |
3. DIY vs. Professional Technician Matrix
🛑 WARNING: Operating your Mitsubishi aircon system with active high-severity error codes (such as U1, U2, UF, or E6) can cause permanent compressor damage or electronic controller burnout.
🟢 Safe to DIY / Self-Check:
- Filter Cleaning (P6): Wash and dry indoor mesh air filters every 2–4 weeks to prevent airflow restriction and freezing.
- Power Reset: Execute a 5-minute hard power reset at the main wall switch to clear temporary electronic glitches.
- Drain Inspection (P4, P5): Check visible drainage outlets for external clogs or slow water flow.
🔴 Requires Professional Repair:
- Sensor & Thermistor Faults (P1, P2, U3, U4): Multimeter resistance testing and part replacement by a qualified technician.
- Refrigerant Leaks & Pressure Issues (U1, U2): Nitrogen pressure testing, leak sealing, and precise gas recharging.
- Electrical & Inverter Board Repairs (E6, U6, UF): High-voltage board diagnostics, communication wiring repair, or compressor troubleshooting.
