Mitsubishi Electric E6 error code: indoor to outdoor communication fault
Mitsubishi Electric E6 means the indoor and outdoor units stopped exchanging signals. What the three-wire link carries, how E6 relates to E7, and where owner checks stop.
What this means
Mitsubishi Electric assigns E6 to a communication error between the indoor and outdoor units, detected on the indoor side. The two ends have stopped exchanging their signal over the connecting cable, so the code identifies a broken conversation rather than a specific failed board.
Equipment and model context
Mitsubishi Electric M-Series and Mr Slim systems that publish the E-series communication table
- MSZ-GL
- MSZ-AP
- MSZ-FH
- MUZ paired outdoor units
This meaning follows Mitsubishi Electric literature for the M-Series and Mr Slim families that publish an E-series table with E6 and E7. Mitsubishi Heavy Industries and other brands assign these characters differently, so confirm both model numbers before applying this page.
What you may notice
- The indoor unit shows E6, or on a wireless-remote system the operation lamp flashes a count the manual reads as E6, and normal running stops.
- The outdoor unit may sit idle, or start and then stop, while the indoor unit reports the fault.
Likely causes
- Loose, reversed, damaged, or corroded conductors at the S1, S2, S3 terminals, or a poor joint where the interconnecting cable was extended, can break the signal path.
- A failed communication circuit on the indoor or the outdoor control board, or a power supply problem at one end, can stop the exchange with the wiring intact.
Diagnostic paths
E6 appeared straight after installation or an electrical repair
The system was worked on, the interconnecting cable was connected, extended, or re-terminated, and E6 has shown ever since with no period of normal running in between.
Have the installer return to check the S1, S2, S3 connections for polarity, tightness, and conductor damage at both ends. Work on the cable is the first thing to confirm before any board is considered.
E6 arrived on a system that had been running for years
The unit had worked normally for a long time, nothing was serviced, and E6 appeared on its own, perhaps after a storm or a power cut.
Record the date and any supply event, then arrange a technician to isolate power and measure the connections and the board communication circuits. A path that fails after long service points at a joint or a board.
Mitsubishi Electric splits connect the indoor and outdoor units with a three-conductor cable at S1, S2, and S3. Power and the communication signal share that run, and E6 says the signal is not getting through.
- Indoor control boardGenerates the signal and waits for a reply
- S1 S2 S3 terminals indoorsFirst set of screwed joints in the path
- Interconnecting cableThree conductors carrying power and the signal
- S1 S2 S3 terminals outdoorsSecond set of screwed joints in the path
- Outdoor control boardAnswers the indoor unit over the same conductors
| Code | Where it is detected | What that suggests |
|---|---|---|
| E6 | Indoor unit reports no valid reply from outdoor | The indoor side is not hearing the outdoor side |
| E7 | Outdoor unit reports a signal transmission problem | The outdoor side is not receiving or sending correctly |
| E6 and E7 alternating | Both ends see the fault at different moments | An intermittent break in the shared path rather than one board |
E6 is about a conversation, not a component
Mitsubishi Electric wall splits use a shared three-wire connection. S1 and S2 carry the power feed to the outdoor unit, and S3 carries the communication signal referenced to S2. The indoor board sends data out and expects the outdoor board to answer within a set time. E6 is raised on the indoor side when those answers stop arriving, which is a statement about the link, not about which board or wire is at fault.
That is why E6 cannot be read as a board fault. The same code appears whether a terminal screw has loosened, a conductor was nicked when the cable was cut to length, the S2 and S3 wires were crossed, or a communication circuit has failed at either end. A technician proves the path in order, from terminal to terminal, before naming a part.
What is worth recording before the visit
Two things cost nothing and shorten the diagnosis. The first is identity: photograph the rating labels on both the indoor and the outdoor unit, because the E-series table and the connection details vary between families and a technician arriving with the wrong manual loses time. The second is history: note when E6 first appeared, whether any installation or electrical work preceded it, whether the code clears on a power cycle and for how long, and whether the outdoor unit runs at all while E6 shows.
If the display alternates between E6 and E7, write that down too. E7 is the matching fault seen from the outdoor side, and the two swapping back and forth points at an intermittent break in the shared path rather than a hard failure at one end, which is a connection a meter can miss if it is measured while the fault happens to be absent.
What to give the technician
Give the technician both rating labels, the date E6 first appeared, any preceding installation or electrical work, how long a power cycle keeps it clear, and whether the display alternates between E6 and E7.
Safe homeowner checks
- With the system off at the isolator, check for any obvious damage to the visible run of interconnecting cable and confirm no recent storm, outage, or rodent activity.
- Record when E6 started, whether it followed any install or electrical work, and whether the outdoor fan turns while the code is shown.
Is a reset appropriate?
Cycling the isolator once shows whether E6 clears on a restart. A code that comes straight back means the link is still down, and each extra reset only wipes timing a technician wants.
When to call a technician
- Inspecting the S1, S2, S3 terminals, testing conductor continuity, and checking the board communication circuits all require isolating power and belong with a qualified technician.
Questions people ask about this
Is Mitsubishi E6 a wiring fault or a board fault?
The code does not separate them. E6 means the indoor unit is not getting valid replies from the outdoor unit. A loose or reversed conductor, a damaged cable, or a failed board circuit all produce it.
What is the difference between E6 and E7?
E6 is detected on the indoor side, meaning it is not hearing the outdoor unit. E7 is detected on the outdoor side. The two alternating points at an intermittent break in the shared connection.
Why did E6 start right after my installer left?
Work on the interconnecting cable changes the path the code watches. A loose S1 to S3 terminal, a crossed pair, or a nicked conductor reads as a failed conversation. Ask the installer to prove the connection before ordering parts.
Evidence recordHow this page was checked
official manufacturer support article · checked 2026-09-09
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Mitsubishi Electric and Mitsubishi Electric Trane HVAC US technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- official manufacturer support article
- Scope of the definition
- Mitsubishi Electric M-Series and Mr Slim systems that publish the E-series communication table
- Last checked
- 2026-09-09