Common Mitsubishi Electric City Multi / Mr. Slim commercial VRF fault codes, what they mean, and whether it's safe to reset or needs a professional. Newer City Multi systems also show 4-digit codes on the outdoor PCB or AE-200 controller for more detail.
Reviewed by Lim Eng Yew (Ryder Lim), Founder & Managing Director, RY Lim Electrical & Aircond Engineering · Last reviewed: September 2026
| Code | Meaning | Common Cause | Action |
|---|---|---|---|
| Communication Codes | |||
| E6 / E7 | Indoor ↔ outdoor unit communication error | Wiring fault on the interconnecting cable, or a control board fault | Check First |
| EE | Communication error (indoor ↔ outdoor) | Same family as E6/E7 — check wiring and connections first | Check First |
| U3 / U4 | Open or short circuit on outdoor unit thermistors | Faulty sensor or wiring to the outdoor unit | Check First |
| Remote Controller Codes | |||
| E1 – E3 | Remote controller transmission error | Faulty remote, wiring, or address conflict on the control bus | Informational |
| E4 | Remote controller signal receiving error | Signal interference or wiring fault | Informational |
| Sensor & Protection Codes | |||
| P1 | Intake (room) sensor error | Faulty room temperature sensor | Informational |
| P2 / P9 | Pipe (liquid or 2-phase) sensor error | Faulty pipe thermistor, open or short circuit | Informational |
| P6 | Freezing / overheating safeguard triggered | Blocked airflow, dirty filter, or low refrigerant | Check First |
| P8 | Pipe temperature error | Abnormal pipe temperature, can follow a refrigerant leak | Call Technician |
| PA | Forced compressor stop | Safety shutdown — often follows a high-severity fault upstream | Call Technician |
| Compressor & Refrigerant Codes | |||
| U1 – Ud | Abnormal high pressure or overheating safeguard | Blocked coil, dirty filter, or struggling outdoor fan | Call Technician |
| U2 | High discharge temperature or insufficient refrigerant | Refrigerant leak or shortage — a common leak-indicator code | Call Technician |
| UF | Compressor overcurrent (locked) | Compressor mechanical or electrical fault | Call Technician |
| UP | Compressor overcurrent interruption | Electrical fault or compressor overload | Call Technician |
E6/E7 is an indoor-to-outdoor communication error — the most common Mitsubishi fault. It usually points to a wiring problem on the interconnecting cable or a control-board fault, and needs a technician to trace.
U2 indicates high discharge temperature or insufficient refrigerant — commonly a sign of a refrigerant leak. This is a high-severity code: switch the system off and have it checked rather than continuing to run it, as a slow leak can turn a minor repair into compressor damage.
Newer City Multi VRF systems can display 4-digit codes (e.g. 1302, 6607) on the outdoor PCB or a centralised controller in addition to the 2-digit codes covered here. Where a fault has both formats, the 2-digit code is what most site controllers and remotes show.
Send us a photo of the code and we'll help you understand it before booking a visit.