Mitsubishi Electric E9 Error Code: Indoor/outdoor communication error (transmitting)
Updated October 2026 · Sourced from Mitsubishi Electric documentation
🧭 Check a few things first
The outdoor unit reports a communication error in transmitting to the indoor unit.
Is it safe to keep running? Check the steps below first. If E9 returns, a technician needs to check the wiring and the outdoor board.
E9 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| E9 Wireless remote: second self-check pattern (errors found by the outdoor unit), 1 flash; wired remote shows E9 | Indoor/outdoor communication error (transmitting) | PLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual) |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Make sure the outdoor unit has power, then turn the breaker off for a minute and back on.
🛑 Stop and call a licensed pro if
- If E9 returns, a technician needs to check the wiring and the outdoor board.
- Any code pointing to refrigerant, the compressor, high pressure or the outdoor unit board. Refrigerant work legally needs a certified technician.
- Burning smell, sparks, or a breaker that trips again after a reset.
- Water leaking from the indoor unit that does not stop after the drain is clear.
Safe first steps for any Mitsubishi Electric code
- Write down the exact code and how it shows (remote display or number of lamp blinks). Similar codes mean different things on different series.
- Turn the system off at the remote, switch off the breaker or disconnect for the unit, wait a few minutes, then turn it back on.
- Clean or replace the indoor unit air filters, and make sure nothing blocks the indoor or outdoor unit.
- Check that the condensate drain line is not blocked or kinked where you can see it.
- Replace the remote controller batteries if the display is dim or the unit does not respond.
Source: Mitsubishi Electric PLA-RP BA Service Manual OCH416 Rev. D, p.22. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
Shaun Cain · Certified HVAC & Refrigeration Technician · Ask an HVAC technician
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