Communication Code, Mitsubishi Electric
Mitsubishi E6 Error Code
The Mitsubishi E6 error code means two very different things depending on which Mitsubishi you own. On Mitsubishi Electric systems, E6 says the indoor unit has stopped hearing from the outdoor unit. On Mitsubishi Heavy Industries systems, E6 points to an indoor coil sensor. This page focuses on Mitsubishi Electric and explains the MHI meaning clearly too.
Check Your Badge
Which Mitsubishi Is Showing E6?
This is one of the clearest examples of why the brand badge matters. Two separate manufacturers use the code E6, yet they mean completely different faults. Reading the wrong explanation could send you, or a technician, looking in the wrong place.
Mitsubishi Electric E6
An indoor and outdoor communication error on the receiving side. The indoor board has not received a valid signal from the outdoor unit for several minutes. Most of this page covers this meaning.
Mitsubishi Heavy Industries E6
An indoor heat exchanger sensor error. MHI manuals link E6 to the indoor coil thermistor reading out of range. It is a sensor fault, not a communication fault.
To check, look at the front of the indoor unit and the compliance label on its side. Mitsubishi Electric wall units commonly carry MSZ model numbers. MHI wall units commonly carry SRK model numbers. If the label is hard to read, take a photo and send it through when you book.
Mitsubishi Electric Meaning
What Does E6 Mean on a Mitsubishi Electric System?
A split system is really two machines talking to each other. The indoor unit reads the room and your settings. The outdoor unit runs the compressor and fan. They swap messages constantly through the connecting cable that links them.
On Mitsubishi Electric units, E6 means the indoor board stopped receiving usable messages from the outdoor side. Service manuals describe the trigger in general terms. If no valid signal arrives for several minutes after power on, or for a few minutes during operation, the indoor board raises E6.
Without that conversation, the indoor unit cannot control the compressor. So it stops and asks for help. The fault could be in the cable, at either terminal block, on either board, or in something on the outdoor side that interrupts communication.
Spotting E6
How Is E6 Displayed on Mitsubishi Electric Units?
On systems with a wired controller, E6 usually appears directly on the screen. Ducted and cassette owners will mostly see it this way, sometimes with a unit address alongside.
With a wireless remote, Mitsubishi Electric ducted and cassette ranges often support a check mode. You enter check mode on the remote, point it at the indoor unit, and count the response. Several manuals link E6 and its sister code E7 to three beeps and three lamp flashes.
Wall splits like the MSZ-AP range may show a three blink pattern on the operation lamp, followed by a pause. Service documents describe that pattern as no serial signal from the outdoor unit, which is the same idea in lamp form. Note the pattern carefully, because counting quickly can be tricky.
Causes
What Causes E6 on Mitsubishi Electric Air Conditioners?
Communication faults have a fairly predictable list of causes. Mitsubishi Electric service documents point to the cable, the boards and some outdoor components. Here they are, roughly from simplest to most involved.
Cable and Terminal Causes
- A loose terminal screw at the indoor or outdoor terminal block.
- Corroded terminals, especially at the outdoor unit in coastal areas.
- A damaged connecting cable, perhaps chewed, crushed or cut during other work.
- Wires connected in the wrong order after installation or relocation.
Board and Component Causes
- Electrical noise on the connecting cable interfering with signals.
- A fault in the indoor board’s transmit and receive circuit.
- A fault in the outdoor board’s transmit and receive circuit.
- On some models, a faulty outdoor fan motor or an open resistor on the outdoor noise filter board.
Interestingly, the outdoor fan motor appears in some Mitsubishi Electric outdoor manuals as an E6 cause. A failing motor can drag down the outdoor board’s supply, which interrupts communication. That is one reason a technician may test the fan during an E6 call.
Owner Steps
What Can I Check Safely for E6?
Most E6 causes involve live terminals, so owner checks stay outside the units. The steps below are safe and often helpful.
- Check whether the outdoor unit is running at all. Silence while the indoor unit shows E6 is useful information.
- Look at your switchboard for a tripped breaker, particularly if the outdoor unit has its own circuit.
- Check whether there is an outdoor isolator switch near the condenser and whether it appears to be on. Do not open its cover.
- Reset power once at the breaker, waiting several minutes before restoring it.
- Look along visible sections of cable for damage from gardening, pets or recent building work, without touching it.
- Note any recent storm, power outage or electrical work in the home.
Do not open terminal covers on either unit, and never test or touch the connecting cable terminals. On many Mitsubishi Electric splits, that cable carries mains power as well as the signal, so it is dangerous to handle.
Technician Process
How Does a Technician Fix a Mitsubishi Electric E6?
A licensed technician works through E6 in a careful sequence. Each step narrows down which part of the communication chain has failed.
Read Both Sides
They check the error history on the indoor unit and read the diagnostic display on the outdoor board. Matching codes on both sides help locate the fault.Isolate and Inspect Terminals
With power off, they open both terminal blocks and check the connecting wires for looseness, correct order and corrosion.Test the Cable
Each core of the connecting cable is tested for breaks or shorts. Suitable test methods are used, since some insulation testers can damage this circuit.Check Outdoor Components
On models where the manual lists them, the outdoor fan motor and noise filter resistor are tested. Disconnecting a suspect fan motor and powering up can reveal whether it is dragging the board down.Assess the Boards
If the wiring and outdoor parts test good and E6 still returns, the indoor or outdoor board becomes the suspect, and the technician confirms which one before replacing anything.
Many E6 repairs end at the terminal block or cable. A board replacement is a bigger job, and the technician will explain why it is needed before going ahead.
The MHI Meaning
What If My Mitsubishi Heavy Industries Unit Shows E6?
If your badge says Mitsubishi Heavy Industries, the story changes. On MHI systems, E6 is an indoor heat exchanger sensor error. The thermistor on the indoor coil is reading out of range, so the board cannot monitor the coil properly.
MHI sensor faults usually come down to a loose plug, a damaged lead or a failed thermistor. Occasionally the indoor board input is responsible. A technician would measure the sensor against its expected values, inspect the plug and lead, and replace whatever is faulty.
Owner checks for an MHI E6 are similar to any sensor fault. Note the code, reset power once, and book if it returns. On SRK wall splits, the RUN and TIMER lights may flash a pattern instead of a code, and the user manual links one RUN flash, with the TIMER light on, to an indoor heat exchanger sensor fault on some ranges.
Inside the Link
What Travels Along the Connecting Cable?
It helps to know what that cable actually carries. On many Mitsubishi Electric split systems, the connecting cable between the indoor and outdoor units has three cores, usually marked S1, S2 and S3 at each terminal block. Together, they deliver power to the outdoor unit and carry the data that keeps both halves in step.
The indoor unit sends instructions such as the target compressor speed, the operating mode and defrost requests. The outdoor unit replies with its own readings and status. This happens continuously, many times a minute. If the messages stop or become garbled, neither side can safely carry on.
Power
On many models, mains power for the outdoor unit runs through the same cable. That is why the terminals are hazardous and why owners should never touch them.
Signal
A low voltage data signal shares the cable. Electrical noise, corroded terminals or a damaged core can distort it enough to trigger E6.
Order
The cores must land on matching terminals at both ends. Swapping two of them during installation or relocation can stop communication completely.
Because power and signal travel together, a single loose screw can cause odd symptoms. The outdoor unit may start, stop, or not respond at all. When you call, describe exactly what each unit was doing, as it guides the technician’s first checks.
Safety
Is It Safe to Keep Trying to Run the System With E6?
On Mitsubishi Electric units, the system cannot run properly without communication, so it will stop. Repeatedly resetting it will not repair a cable or board fault, and it may stress components on each start attempt.
More importantly, E6 sometimes follows electrical damage. A storm surge, a burnt terminal or a rodent chewed cable can all cause it. If you notice a burning smell, scorch marks or a tripping breaker, switch the system off at the switchboard and leave it off.
For MHI units showing E6, the unit stops because it cannot protect the coil. Again, the right move is one reset and then a booking if the code returns.
Environment
Do Storms and Coastal Air Cause E6?
They are two of the biggest contributors. Communication circuits are sensitive to voltage spikes. A thunderstorm can send a surge through the supply, and a brief outage can leave boards in an odd state. Many E6 codes that appear immediately after a storm clear with a single reset. Others reveal real damage to a board or terminal.
Coastal suburbs bring a slower threat. Salt air settles on outdoor units in beachside parts of Perth, Adelaide, Sydney and Melbourne. Over time, it creeps into terminal blocks and corrodes the connections. A terminal that looks fine can carry a resistive joint that disrupts signals.
Summer heat adds stress too. Outdoor boards sit inside a metal case in full sun in Brisbane or Perth summers, and electronic parts age faster when hot. Shade for the outdoor unit, where it does not restrict airflow, can help. Finally, rodents and possums sometimes chew cables in roof spaces and wall cavities, so pest activity is worth mentioning.
Related Codes
Which Codes Are Related to E6?
Mitsubishi Electric uses a small family of communication codes. Each tells you which side detected the problem, which helps narrow the search.
E7, Indoor Side
E7 means the indoor board sent data but read back the wrong values repeatedly. It leans slightly more towards the indoor board or electrical noise.
E8 and E9, Outdoor Side
These are the outdoor unit’s versions. E9 is the outdoor transmitting error, raised when the outdoor board cannot get its message through.
E0 to E4, Remote Side
These relate to the remote controller and indoor unit link, rather than the indoor to outdoor link. They tend to be easier faults to fix.
Browse every confirmed code on the Mitsubishi error codes hub, or compare with other makes in the main error codes library.
Getting a Technician
How Do I Book an E6 Repair in My City?
Rapid Air Cooling handles the booking and dispatches an independent licensed technician. We are not a Mitsubishi dealer and do not claim manufacturer accreditation. Electrical work is carried out by technicians who hold the licences their work requires.
Choose your city to get started. In Sydney, visit air conditioner repairs Sydney or the Sydney Mitsubishi page. Melbourne owners can use Melbourne repairs. In Brisbane, there is Brisbane repairs. In Perth, see Perth repairs and Mitsubishi in Perth. Adelaide owners can use Adelaide repairs.
Our national Mitsubishi air conditioning page covers both makers. For other symptoms, browse the troubleshooting guides, or read about our air conditioning service Australia wide.
Good to Know
What Are the Less Obvious E6 Clues?
Open more detail
Timing helps. An E6 that appears straight after power on suggests a wiring order problem or a dead outdoor board. An E6 that appears mid operation suggests an intermittent connection, noise, or a component that fails when warm.
Recent work matters a great deal. If the system was just installed, relocated or had its outdoor unit replaced, wiring order at the terminals is a prime suspect. If an electrician recently worked on the switchboard, the outdoor supply may have been changed.
Multi head systems add complexity. Each indoor unit has its own connecting cable to the shared outdoor unit. If only one head shows E6, the fault is likely on that head’s cable or board. If every head shows it, the outdoor unit or its supply is more likely.
Older homes sometimes have long cable runs between units, perhaps from a back bedroom to a side passage. Longer runs give more chance of damage and more exposure to noise from other appliances. A technician may suggest rerouting or replacing a tired cable if it is brittle or patched.
Finally, avoid running the system from a portable generator or unusual power source unless it is designed for it. Unstable power can cause communication faults, and it can damage sensitive inverter electronics.
Questions
Frequently Asked Questions
Does E6 mean the same thing on every Mitsubishi?
No. On Mitsubishi Electric, E6 is an indoor to outdoor communication error. On Mitsubishi Heavy Industries, E6 is an indoor coil sensor fault. Check the badge first.
My outdoor unit is silent and the indoor shows E6. What now?
Check the switchboard for a tripped breaker, then reset power once. If the outdoor unit stays silent and E6 returns, book a technician to check the supply, cable and boards.
Can a storm cause E6?
Yes. Surges and outages can upset or damage communication circuits. A reset may clear a temporary glitch, but a recurring E6 after a storm suggests damage needing repair.
Why would the outdoor fan motor cause a communication code?
On some Mitsubishi Electric models, a faulty outdoor fan motor can pull down the outdoor board’s supply, disrupting communication. Technicians test for this on relevant models.
Is it safe to check the connecting cable myself?
No. On many splits, that cable carries mains voltage. Look only at visible sections from a distance and leave terminal work to a licensed technician.
Is E6 expensive to fix?
It depends on the cause. A loose terminal or damaged cable is relatively simple. A board replacement costs more. The technician will diagnose before quoting any major work.
Why did E6 appear after my system was moved?
Relocation means disconnecting and reconnecting the cable. Wires connected in the wrong order or left loose are common reasons for E6 afterwards.
Other Brands
What Does E6 Mean on Other Brands?
The E6 code is used differently by other manufacturers. Compare the meanings side by side before you book.
Indoor and Outdoor Units Not Talking?
Call us with the code and brand badge details, and we will book a licensed technician to trace the fault.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles