Indoor and Outdoor Unit Communication Error
What it means
This code appears on the wired remote of Mitsubishi Electric Mr. Slim ducted, ceiling and cassette units. It means the indoor unit is not receiving a valid signal from the outdoor unit over the connecting cable. The outdoor unit stops and there is no cooling until communication is restored. The same code can mean something else on other brands, and wall-mounted Mitsubishi Electric models show errors as lamp blinks with a different meaning.
Models covered: Mitsubishi Electric ducted, ceiling and cassette units (Mr. Slim) with check codes on the wired remote; wall-mounted Mitsubishi Electric models may show errors as lamp blinks with a different meaning.
Symptoms4
- The indoor fan runs while the outdoor unit stays completely off.
- E6 appears a few minutes after start or right after a power cut.
- The code comes and goes with voltage swings or after rain.
- In some cases the outdoor unit board shows no lights at all.
Possible causes5
- Loose terminals or wrong terminal order on the interconnecting cable.
- No power to the outdoor unit from a tripped breaker or blown fuse.
- A cable damaged by heat, sun, rodents or water in the joints.
- Electrical noise from nearby cables or poor earthing.
- A faulty outdoor or indoor control board.
How to diagnose6
- Switch off at the breaker for several minutes and restart; sometimes the error is a one-off after a power cut.
- Make sure the outdoor unit breaker, if separate, is on.
- Switch off at the breaker before opening any panel; the outdoor unit and its inverter board keep a dangerous charge for a while after switch-off.
- The technician checks the interconnecting cable terminals at both units for order, tightness, water and corrosion.
- The technician measures the supply reaching the outdoor unit and reads the diagnostic LEDs on its board per the service manual.
- If the wiring is sound, both control boards are checked to find the faulty side.
How to fix6
- Retighten the interconnecting cable terminals and correct their order.
- Replace the fuse or restore the supply to the outdoor unit.
- Replace a damaged interconnecting cable and route it away from high-voltage cables.
- Improve earthing and fit a voltage protector if the supply fluctuates.
- Replace the faulty outdoor or indoor control board.
- Run the system and confirm stable communication and no code.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
The cost is low for a loose terminal or cable, and rises sharply if the outdoor unit needs a new inverter board.
Prices are rough estimates including the part and the technician’s fee, and vary with brand, model and part source.
Prices last updated: September 2026
Frequently asked questions
Is E6 an indoor or outdoor fault?
It can be either unit or the cable between them, so the technician starts with power and wiring before judging any board.
Why does E6 appear after a power cut?
The outdoor board may start late or be upset by voltage swings when power returns, and the code clears after a restart; if it keeps coming back, there is a real fault.
Can I check the wiring myself?
It is not recommended. The outdoor unit carries dangerous voltage and its board stays charged after switch-off, so leave it to a technician.
This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.
Report a mistake
Spotted something inaccurate? Tell us and we will review and correct it.
Report received — thank you
This is your private tracking link. It shows the status and our reply as soon as it is posted.
The link is saved in this browser only.