Mini split communication wire
Use for E1 or E6 faults after terminal checks confirm a damaged indoor-to-outdoor wire run.
$25-$110
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Mitsubishi Mini Split Error Codes — Quick Reference
Mitsubishi mini-split error codes appear on the indoor unit’s LED display and on the wireless remote controller. Codes fall into three families: E-codes (communication and sensor faults), U-codes (protection/system faults), and P-codes (abnormal operation faults). Retrieve codes by pressing the CHECK button on the remote or observing the fault display on the indoor unit.
| Code | Meaning | Quick Fix |
|---|---|---|
| E1 | Indoor/outdoor communication fault | Check signal wire connections |
| E3 | Indoor PCB fault | Replace indoor PCB |
| E4 | Outdoor PCB fault | Inspect outdoor board and fuses |
| E5 | Outdoor overcurrent | Check outdoor fan and refrigerant |
| E6 | Communication error (indoor-outdoor) | Check wiring and terminal block |
| E7 | Outdoor fan motor fault | Check fan blade and motor |
| E9 | Expansion valve fault | Replace expansion valve |
| U1 | Reverse phase / power supply abnormality | Check 3-phase power (commercial units) |
| U2 | Low voltage / power supply fault | Check supply voltage |
| U3 | Discharge temperature too high | Check refrigerant charge |
| U4 | Communication between remote and indoor | Check signal wiring |
| U6 | Compressor overcurrent | Check compressor; refrigerant charge |
| P1 | Indoor intake air temp sensor fault | Replace thermistor |
| P2 | Indoor pipe temp sensor fault | Replace pipe thermistor |
| P4 | Drain system fault | Clean drain pan and pump |
| P5 | Drain pump fault | Inspect drain pump |
| P6 | Freeze protection / heating overheat | Refrigerant issue or blocked airflow |
| P8 | Outdoor unit fault | Check outdoor coil and fan |
Technician Tips
Mini-split and VRF faults usually come from condensate drainage, thermistors, indoor-outdoor communication wiring, outdoor airflow, inverter protection, or control-board inputs. Match the code to the exact indoor and outdoor model, then check filters, drains, coils, wiring terminals, and sensor seating before replacing electronics.
DIY vs Pro: Cleaning filters, clearing drains, checking obvious loose connectors, and power-cycling once are reasonable first steps. Refrigerant work, inverter-board diagnostics, high-voltage testing, and sealed-system repairs need a qualified HVAC technician.
Need Replacement Parts?
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom. Check Mitsubishi mini split communication wire, remote, thermistor, drain pump, and drain cleaning parts on Amazon - prices and availability change frequently.
Most Common Codes
E1: Indoor-Outdoor Communication Fault
The indoor and outdoor units have lost communication on the signal wire. Check the 3-wire connection between indoor and outdoor units at both terminal blocks. Wires should be connected to terminals 1, 2, and 3 in the same order at both ends. A loose terminal screw or corroded connection causes intermittent E1 faults.
E6: Communication Error
Similar to E1 but triggered differently by the control board. On Mitsubishi M-Series and Mr. Slim systems, verify all communication wiring is correct. For multi-zone (MXZ) systems, check wiring to each indoor head. Also check that the outdoor unit’s dip switches match the system configuration.
U4: Remote-to-Indoor Communication
The wireless remote and the indoor unit are not communicating. Replace the remote batteries first. If that doesn’t fix it, the remote receiver PCB on the indoor unit may be faulty. Test by using a replacement remote or the Kumo Cloud app if installed.
U6: Compressor Overcurrent
The compressor is drawing excess current. Causes: low refrigerant charge (undercharge causes high current at the compressor), dirty outdoor coil (causes high discharge pressure and current), or a failing compressor. Check the outdoor unit coil for debris and clean if needed.
P1: Indoor Thermistor Fault
The indoor air temperature sensor (thermistor) has failed or its connector is loose. Locate the small thermistor plug on the indoor PCB — unplug and re-seat it. If code P1 remains, measure thermistor resistance at room temperature (typically 10 kΩ at 77°F / 25°C). Out-of-spec resistance means the thermistor needs replacement.
P4: Drain System Fault
The float switch in the drain pan has detected standing water — the drainage system is not keeping up. This usually means: (1) the drain line is blocked or kinked, (2) the drain pump has failed, or (3) the float switch itself is stuck. Clear the drain line first (wet-vac from the drain outlet). If water was standing in the pan, let it drain and clear P4 by cycling power.
P5: Drain Pump Fault
Specifically indicates the drain pump has failed or is not being detected. The pump is a small submersible pump in the indoor unit’s drain pan. Check that it’s plugged in to the PCB. If plugged in and code persists, replace the pump assembly.
When to Call a Pro
U3 (high discharge temperature) and U6 (compressor overcurrent) often indicate refrigerant issues that require a certified HVAC-R technician to diagnose and repair. Don’t ignore these — running a mini-split with incorrect refrigerant charge causes compressor damage.