M
Mitsubishi Electric Error Codes
Mr. Slim, City Multi, and Mini-Split Systems
Quick Reference: Error Code Types
E_
Communication
P_
Indoor/Sensor
U_
Outdoor/Compressor
4-digit
City Multi/VRF
Communication Errors
| Code | Description | Possible Cause | Solution |
|---|---|---|---|
| E0/E3 | Remote controller signal receiving error | Wiring issue between remote and indoor unit | Check remote controller wiring connections |
| E1/E2 | Remote controller board error | Remote PCB malfunction | Replace remote controller |
| E6 | Indoor/outdoor unit communication error | Signal wire fault or PCB issue | Check S1/S2/S3 wiring, verify polarity |
| E7 | Outdoor unit communication error (City Multi) | Communication between outdoor units | Check inter-unit wiring, address settings |
| E9 | Indoor/outdoor communication error (intermittent) | Loose connection or interference | Tighten connections, check for noise sources |
| Eb | Communication error between indoor units | Multi-indoor unit comm fault | Check indoor unit addressing and wiring |
Sensor Errors
| Code | Description | Possible Cause | Solution |
|---|---|---|---|
| P1 | Intake sensor error | Room temperature sensor fault | Check thermistor resistance, replace if faulty |
| P2 | Pipe (coil) temperature sensor error (TH2) | Indoor coil thermistor fault | Check thermistor connection and resistance |
| P4 | Drain sensor error | Drain sensor or float switch fault | Check drain sensor, clean float mechanism |
| P5 | Drain pump error | Drain pump motor or float switch | Check pump operation, clean drain system |
| P6 | Freeze/overheat protection | Coil temp too low/high | Check airflow, filter, refrigerant charge |
| P9 | Pipe temperature sensor 2 error (TH5) | Secondary coil thermistor fault | Check and replace thermistor |
| PA | Forced compressor stop (accumulator) | Liquid refrigerant in suction line | Check TXV/EEV, indoor coil airflow |
Compressor & Outdoor Errors
| Code | Description | Possible Cause | Solution |
|---|---|---|---|
| P8 | Pipe temperature abnormality | Outdoor coil thermistor error or frost | Check thermistor, verify defrost operation |
| U1 | High pressure protection | High head pressure cutout | Clean condenser, check fan, verify charge |
| U2 | Low pressure / no refrigerant | Low refrigerant or compressor fault | Leak test system, check compressor |
| U3 | Short cycle (outdoor) | Rapid on-off cycling detected | Check refrigerant charge, HP/LP switches |
| U4 | Outdoor thermistor error (TH3) | Outdoor ambient sensor fault | Check and replace thermistor |
| U5 | Condenser coil thermistor error | Condenser temp sensor fault | Check and replace thermistor |
| U6 | Compressor overcurrent (soft) | Compressor drawing excess current | Check compressor, voltage, refrigerant |
| U7 | Low super heat (City Multi) | Excessive liquid return | Check EEV operation, charge level |
| U8 | Outdoor fan motor abnormal | Fan motor lock or feedback error | Check fan motor, blade obstruction |
| U9 | Abnormal voltage at DC voltage | Inverter power circuit issue | Check inverter board, power supply |
| UA | Compressor overcurrent (hard) | Severe overcurrent protection | Check compressor windings, inverter board |
| Ub | Discharge thermistor error (TH4) | Compressor discharge sensor fault | Check and replace thermistor |
| UE | Compressor overheat protection | Discharge temp too high | Check refrigerant charge, compressor |
| UF | Compressor motor overcurrent | Compressor winding issue | Megohm test compressor, replace if failed |
| UP | Compressor overcurrent (trip) | CT sensor detected overcurrent | Check compressor, inverter board |
Inverter & PCB Errors
| Code | Description | Possible Cause | Solution |
|---|---|---|---|
| 0403 | Current sensor error | Inverter current sensor fault | Check current transformer, inverter board |
| 1102 | Compressor start failure | Compressor won't start | Check compressor, wiring, capacitor |
| 1105 | Compressor overcurrent | Instantaneous overcurrent | Check compressor windings, inverter |
| 1108 | Compressor desync | Loss of compressor synchronization | Check inverter board, compressor |
| 1302 | DC link overvoltage | DC bus voltage too high | Check power supply, inverter board |
| 1500 | AC overcurrent | AC line current too high | Check power supply, wiring |
| 2500 | Heat sink overheat | Inverter overtemperature | Check ventilation, heat sink |
| 2502 | Heat sink thermistor error | Inverter temp sensor fault | Check thermistor, inverter board |
| 4102 | High pressure sensor error | HP transducer fault | Check pressure sensor |
| 4106 | Low pressure sensor error | LP transducer fault | Check pressure sensor |
| 4235 | Suction gas superheat low | Liquid returning to compressor | Check EEV, metering device |
| 4250 | Discharge temp high | Compressor overheating | Check refrigerant charge, valves |
| 5101 | Inverter communication error | Inverter PCB comm fault | Check inverter board, connections |
| 5102 | Main PCB-Inverter communication | Control board comm fault | Check wiring between boards |
| 6600 | Fan motor overcurrent | Outdoor fan drawing high current | Check fan motor, blade obstruction |
| 6602 | Fan motor rotation error | Fan not rotating correctly | Check fan motor windings, PCB |
LED Flash Codes (Mr. Slim)
| Code | Description | Possible Cause | Solution |
|---|---|---|---|
| 1 Flash | Room thermistor error | Indoor room sensor fault | Check thermistor TH1 |
| 2 Flashes | Indoor coil thermistor error | Coil sensor TH2 fault | Check thermistor TH2 |
| 3 Flashes | Transmission error (sending) | Indoor-outdoor comm error | Check signal wiring |
| 4 Flashes | Transmission error (receiving) | Indoor-outdoor comm error | Check signal wiring, outdoor PCB |
| 5 Flashes | Float switch activated | Drain pan full or switch fault | Clear drain, check float switch |
| 6 Flashes | Freeze protection | Indoor coil freezing | Check airflow, filter, charge |
| 7 Flashes | Overheat protection (indoor) | Coil temp too high | Check operation mode, airflow |
| 8 Flashes | Indoor fan motor error | Fan motor not running | Check motor, capacitor, PCB |
| 10 Flashes | EEV/Valve error | Electronic expansion valve fault | Check EEV coil, wiring |
| 11 Flashes | Indoor/outdoor mismatch | Incompatible units connected | Verify system compatibility |
No matching error codes found
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Mitsubishi Troubleshooting Tips
Reading Error Codes
- Mr. Slim: LED flashes or display on remote/unit
- City Multi: Use MA Remote Controller or MNet system
- 4-digit codes are specific to VRF/City Multi systems
- LED patterns: count green and red flash sequences
Most Common Issues
- E6: Communication error - check signal wiring S1/S2/S3
- P8: Pipe temp error - often defrost or thermistor issue
- U1/U2: Pressure protection - check refrigerant
- P5: Drain issue - clean drain line and pump
Service Mode Access (Mr. Slim)
To access fault history on Mr. Slim units:
- Press and hold TEST button on indoor unit for 5+ seconds
- LED will display fault code history
- Use remote: Press "SET" + "MODE" simultaneously to view codes