Mitsubishi Electric AC Error Code E6 — Communication Error Fix

What Does This Error Mean?

E6 on a Mitsubishi Electric AC means the serial communication link between the indoor and outdoor units has failed. The indoor unit is sending or expecting signals from the outdoor unit and not receiving them. Common causes are a damaged communication wire, a blown outdoor unit fuse, or a PCB fault on either unit.

Affected Models

Mitsubishi Electric MSZ-AP Series
Mitsubishi Electric MSZ-EF Series
Mitsubishi Electric MSZ-GL Series
Mitsubishi Electric MSY Series
Mitsubishi Electric MXZ Multi-Split Series

Common Causes

Communication wire (typically the S-wire in the interconnecting cable) broken, shorted, or disconnected
Outdoor unit fuse blown or circuit breaker tripped
Outdoor PCB fault preventing it from communicating
Indoor PCB fault on the communication circuit
Wiring polarity reversed during installation or after maintenance
Power supply voltage out of specification to either unit

How to Fix It

Check that both the indoor and outdoor units have power.

Mitsubishi Electric systems sometimes have separate circuit breakers for the indoor and outdoor units. Check your electrical panel for any tripped breakers.
Turn off both units at the circuit breaker, wait 60 seconds, then restore power.

A complete power cycle resets the communication protocol on both PCBs simultaneously. E6 caused by a temporary communication glitch after a power outage often clears this way.
Listen for the outdoor unit starting.

After restarting, the outdoor unit should start within 3 minutes of the indoor unit being switched on. A completely silent outdoor unit suggests a power or PCB issue on that side.
If E6 persists after a power cycle, call a technician.

The technician will use a multimeter to test continuity and voltage on the communication wire and identify whether the fault is in the wiring, the indoor PCB, or the outdoor PCB.

When to Call a Professional

If a full power cycle does not clear E6, contact a Mitsubishi Electric authorised technician. Diagnosing which end of the communication circuit has failed requires specialist test equipment.

Frequently Asked Questions

Does E6 mean both units need replacing?

Not necessarily — E6 is often caused by a wiring issue rather than a PCB failure. A loose terminal or damaged cable section is a much cheaper fix than a board replacement. A technician will always check the wiring first before condemning a PCB.

Can E6 appear after a new installation?

Yes — if the communication wires were connected in the wrong order or the S-wire was not connected at all during installation, E6 will appear immediately. This is an installation error and should be rectified free of charge by the installing company.